Formamidinyl Thiazole-Based Palladium Complexes as Efficient Nano-sized Catalysts for Aqueous Suzuki –Miyaura Cross-Couplings

Formamidinyl Thiazole-Based Palladium Complexes as Efficient Nano-sized Catalysts for Aqueous Suzuki –Miyaura Cross-Couplings | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Formamidinyl Thiazole-Based Palladium Complexes as Efficient Nano-sized Catalysts for Aqueous Suzuki –Miyaura Cross-Couplings Afaf Y. Khormi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7546711/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The present work describes a facil access to novel nano-sized thiazole-based palladium(II) complexes from easily accessible starting precursors and elucidation of their structures by spectroscopic tools as well as physical characteristics. The efficiency of the synthesized complexes and their use as precatalysts for Suzuki Miyaura cross coupling reaction was investigated. Thiazole-based palladium(II) precatalysts could catalyze the C-C cross coupling reaction efficiently using water as a solvent under green mild reaction conditions. Formamidinyl thiazoles palladium precatalysts C-C cross-coupling Suzuki-Miyaura Water Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction One of the versatile applications of the palladium complexes their exhibitions in the C-C cross-coupling reactions. These complexes are characterized by high stability and unique reactivity, which depends on the identity of the ligand and the mode of coordination of such ligands to the core palladium atom. Nitrogen containing heterocyclic ligands were usually considered in fitting that demand in the palladium coordination and usually their complexes sound well in the various applications of organic transformations. On the other hand, Suzuki-Miyaura cross-coupling (SMC) reaction is a crucial tool in organic transformation to access a biaryls derivatives with great selectivity and using soft conditions. Biaryls derivatives constitute an essential part in diverse natural products and many pharmaceuticals. In this context, palladium complexes containing a heterocyclic ligand have been used as efficient pre-catalysts for homogenous Suzuki-Miyaura cross-coupling under mild reaction conditions. [1–20] As an aim to our research program, I'm focusing on the use of water as a green solvent to perform the C-C coupling reactions using heterocyclic ligands-based palladium complexes as catalytic precursors, recently i have explored the use of such complexes to catalyse the Suzuki-Miyaura cross-coupling reaction with very excellent outcomes in aqueous media [20–25] On continuing our efforts in the synthesis and catalytic applications of novel complexes, I envisioned the synthesis of new ligands combining a formamidine functionality with a thiazole ring. This 5-membered heterocyclic fragment together with the formamidine moiety can behave as strong N-donors in the developed ligands [26–28]. I believe that this structural combination could provide a targeted stability to the palladium complex formed as well as a better tuning of its catalytic efficiency. I also describe the catalytic applications of these complexes in Suzuki-Miyaura cross-coupling reaction in water. 2. Results and Discussion 2.1. Synthesis of the benzothiazole-based Pd(II) complexes 4a,b Condensation of 2-aminothiazole derivatives ( 1a-d) with N , N -dimethylformamide dimethylacetal (DMF DMA) ( 2 ) furnished the corresponding 2-formamidinylthiazole derivatives ( 3a-d ) as depicted in Scheme 1 . The structural elucidation of 2-formamidinylthiazole 3a-d was achieved by using spectroscopic data and elemental analyses. All the 1 H NMR spectra of the synthesized ligands 3a-d showed two singlet signals of the two magnetically nonequivalent methyl groups of N( Me ) 2 group in the region of δ 2.98 and 3.14 ppm. In addition, the formamidine group proton (-N = C H -) resonates as a singlet in the region of δ 8.27–8.45 ppm (Fig. 1 ). For instance, the 1 H NMR spectrum of the synthesized ligands 3d revealed two singlet signals of the two methyl protons of N( Me ) 2 group in the region of δ 2.99 and 3.13 ppm. The aromatic protons appear as two doublets at δ 7.44 and 7.90. In addition. a singlet signal at δ 7.49 assigned for the thiazole CH proton and the formamidine group proton (-N = C H -) resonates as a singlet in the region of δ 8.36 ppm. 13 C NMR spectra of the same ligand 3d showed the characteristic nonequivalent 10 carbon atoms resonance at their expected chemical shifts as shown in Fig. 1 . Also the 13 C NMR spectra prove the magnetic nonequivalence of the two methyl groups of the N( Me ) 2 group. Considering the IR spectra of the synthesized ligands 3a-d , all ligands spectra revealed the presence of C = N group absorption band at the expected frequency near 1600 cm − 1 (see experimental part). Thiazole-based palladium complexes 4a-d could be accessed by addition of methanolic sodium tetrachloropalladate solution to equimolar amount of formamidinylthiazole ligands 3a-d dissolved in methanol at ambient temperature. Immediate precipitates of the targeted complexes were formed and after complete addition of sodium palladate solution good yields of the corresponding thiazole-based palladium(II) complexes 4a-d were obtained as shown in Scheme 2 . The structural proof of synthesized thiazole-Pd complexes 4a-d was based on the spectroscopic analysis and physical characteristics. 1 H NMR spectrum of 4d (taken as an example) revealed the presence of two singlet signals at δ 3.02 and 3.16 ppm due to the protons of N(Me) 2 group. In addition to two doublets signals at δ 7.46, and 7.91 ppm with J = 8.5 Hz assigned to the two aromatic rings (CH) protons at position 5 and 6 in each phenyl thiazole moiety and two singlet signals at δ 7.54 and 8.44 ppm due the thiazole ring proton and the formamidine moiety proton, respectively. From the values of the chemical shift δ the coordination of the pallidum atom to the ligand molecules caused a general increase in the values of the chemical shifts δ of all protons of the ligand molecule as shown in the comparison Fig. 3 . 2.2. Thermogravimetric analysis TGA/DTA TGA (thermogravimetric Analysis) and DTA (differential thermal analysis) were performed for the four palladium complexes 4a-d to investigate their thermal stability. TGA and DTA analysis were performed under nitrogen flow, in temperature range from ambient (25°C) up to 800°C, with a heating rate of 10°C/min. The obtained TG and DTA thermograms for are shown in Fig. (A) and (B), respectively. All complexes exhibited a similar thermal decomposition behavior, with a high thermal stability up to ~ 250°C for 4b-d and around 225 for complex 4a . The weight loss observed in TGA curves below ~ 250°C and ~ 225°C for samples 4b-d and for sample 4a , respectively, is attributed to the physically adsorbed water and solvent. This weight loss was around 2% for samples 4b-d and around 4.5% for sample 4a . This was clearly observed in 4a DTA curve by an exothermic peak with a maximum at around 140°C. The main weight loss was observed between ~ 225 and ~ 400°C for all samples which attributed to the decomposition of the ligands. This decomposition of the organic matter was observed in DTA curves by endothermic peaks with maximums at ~ 285°C and ~ 275°C for samples 4b, d and 4a, c , respectively. This is corresponding to a weigh loss of 41.54%, 44.6%, 42.33%, and 46.37% for samples 4a-d , respectively. 2.3. The scanning electron microscopy (SEM) The morphology of solid ligands 3b-d and their palladium complexes 4a-d was investigated by scanning electron microscopy (SEM). The obtained micrographs are shown in Figs. 5 – 8 . The SEM images of the complex 4a (Fig. 5 a-c) depicted spherical and uniform particles, with size in the range of 0.94–3.96 µm. The particles size distribution was narrow at around 1.58 µm (Fig. 5 d). The obtained micrographs of the ligand 3b (Fig. 6 e, f) revealed the formation of particles with irregular shape and particles diameter ranges from 0.15 µm to 30 µm. After the complexation of the ligand 3b with palladium, the SEM images of the obtained complex 4b (Fig. 6 g, h) showed the formation of flower-like microspheres with diameter ranges from 0.4 µm to 10.05 µm, and average diameter of 5.58 µm. These flower-like microspheres were formed by rectangular nanoparticles oriented toward the microsphere center (Fig. 6 i), with average length of 3 µm, width average of 0.3 µm, and thickness of around 90 nm (Fig. 6 j). SEM images of ligand 3c (Fig. 7 k, l) showed the formation of thin micro platelets with irregular shape, and size ranges from 1 to 70 µm, with platelets average thickness of around 2.5 µm. After the complexation of this ligand with palladium ( 4c ), the particles shape and size were completely transformed to microspheres (Fig. 7 m, n) with particles size ranges from 1.83 to 9.77 µm, average diameter of 6.08 µm (Fig. 7 o). The further enlargement of 4c SEM micrographs revealed that these microspheres are formed by worm-like nanoparticles with length ranges from 50 to 500 nm (Fig. 7 p). However, the SEM micrographs of the ligand 3d (Fig. 8 q, r) depicted the formation of micro-rectangles with diameter ranges from 5 to 100 µm, and thickness of around 2.5 µm. The SEM images of the corresponding palladium complex 4d (Fig. 8 s-u) revealed the formation of microparticles with irregular shape. The study of the particles size distribution (Fig. 8 v) showed that the particles size ranges from 60 nm to 7.38 µm, and average diameter of 2.15 µm. 2.4. Powder X-ray Diffraction Analysis The powder XRD analysis were performed to investigate the crystallinity of the obtained complexes 4a-d . The obtained results are presented in Fig. 9 . The XRD pattern of complex 4a does not presents any reflections. This is indicating an amorphous structure of this complex. However, the XRD patterns of complexes 4b and 4c recorded three similar main reflections at 2Ɵ = 7.3º, 15.0º, and 26.5º, indicating the existence of crystalline phases. Complex 4d also presents three main reflections at 2Ɵ = 14.6º, 21.3º, and 27.0º, but are different than those observed for complexes 4b and 4c , and less sharp. Suggesting the existence of a crystalline phase in 4d structure. 2.5. Catalytic efficiency of complex 4a-d in Suzuki –Miyaura Cross-Couplings 2.5.1. Effect of concentration of the complex 4a,b in catalysis of Suzuki –Miyaura Cross-Couplings In a systematic study when developing a new catalytic system an investigation of the catalytic efficiency of this system begins with study the concentration limits that affords the high efficiency of the target catalytic system in the mentioned catalysed reaction. Thus, the catalytic efficiency of the developed precatalysts based on the synthesized thiazole-based palladium complexes in C-C cross coupling reaction, have been studied by investigating the concentration effect of the thiazole-based palladium complexes 4a-d on Suzuki–Miyaura Cross-Couplings between p -bromoacetophenone ( 5 ), as a halide component and phenyl boronic acid ( 6 ) as depicted in scheme 3 . Thus, the C-C cross-coupling reaction proceeded in water as a solvent and presence of a mild base, K 2 CO 3 and in the presence of a phase transfer agent, namely tetrabutylammonium bromide (TBAB) as a co-catalyst for the aqueous Suzuki–Miyaura Cross-Couplings under conventional heating conditions. Therefore, performing the cross-coupling reaction in the presence of different concentrations of the the thiazole-based palladium complexes 4a-d with furnished 4-acetyl-1,1´-biphenyl ( 7 ) as the desired cross coupled product, Following up the reaction by TLC showed that, three hours of thermal heating was enough time to access 4-acetyl-1,1´-biphenyl ( 7 ) as illustrated in Scheme 3 and Table 2 . As shown in Table 1 , starting with 1.5 mol% of the appropriate thiazole-based palladium precatalyst 4a-d to catalyse the C-C cross coupling and the molar ratio of p -bromoacetophenone ( 5 ): phenyl boronic acid ( 6 ): K 2 CO 3 : TBAB was 1.0/1.2/1.0 / 0.6, we got 100% conversion with complete disappearance of the starting materials (measured by GC-analysis) and the cross coupled product 4-acetyl-1,1´-biphenyl ( 7 ) was obtained (entry 1, Table 1 ). By gradual decrease in the amount of the used thiazole-based palladium precatalyst 4a-d (from 1.5 to 0.25 mol%), we noticed that a full to excellent GC-conversion using the same cross coupling conditions (entries 2–5, Table 1 ). Thus, thiazole-based palladium precatalyst 4a-d showed similar excellent catalytic efficiency in the C-C cross coupling reaction even when using very low mol% and regardless the nature of the substituent in the thiazole ring. When Suzuki–Miyaura reaction was carried out in absence of thiazole-based palladium precatalyst 4a-d , the starting p -bromoacetophenone ( 5 ) was completely recovered from the reaction mixture as expected as showed in Table 1 , entry 6. The obtained cross coupled product was analyzed and its structure was confirmed by spectroscopic tools. Table 1 Effect of concentration of precatlyst 4a-d on the coupling of 4´-bromoacetophenone ( 5 ) with phenylboronic acid ( 6 ) in water. Entry Pd, mol%% GC Conversion% Precatalyst 4a Precatalyst 4b Precatalyst 4c Precatalyst 4d 1 1.5 96 100 100 100 2 1 91 98 100 100 3 0.75 84 88 93 95 4 0.5 77 83 87 91 5 0.25 62 80 83 88 6 0.00 0 0 0 0 a Conditions: 4´-bromoacetophenone ( 5 ) / phenylboronic acid ( 6 )/ K 2 CO 3 / TBAB / water: 1.0/1.2/1.0 / 0.6/ 10 mL, under thermal heating at 100°C for 3 h. b Conversions were based on GC-analysis: the conversion was monitored by Shimadzu GC-17A gas chromatography (GC), equipped with flam ionization detector and RTX-5 column, 30 m x 0.25 mm, 1 µm film thickness. Helium was used as carrier gas at flow rate 0.6 mL/min. Samples were withdrawn from the reaction mixture periodically. Injection volume was 1 µl, and total flow was 100 ml/min. Oven temperature was initiated at 100°C for 2 min up to 130°C at a rate of 15°C/ min held for 2 min, then increased to 150°C at a rate of 2°C/ min held for 2 min. The Injector temperature was 160°C and the detector temperature was 200°C. In order to explain how the palladium precatalyst 4 take part in the catalytic process of the reaction does, it was suggested that the complex acts as “dormant species” and does not participate in the reaction catalytic cycle in an actual manner. the precatalyst 4 is considered as the main precursor for the palladium catalytically active species, thus it is considered as a precatalyst in the cross-coupling reaction. Generally, the palladium (0) species were the true active catalysts as reported previously [29.30]. Therefore, the precatalyst 4 may serve as a reservoir that is indirectly involved in the catalytic cycle of the cross coupling and it is the main source of release of nano-sized palladium(0) which can afford catalytic role even when used with very low concentrations [31]. As an alternative green methodology for the present cross coupling reaction we have used a hydrothermal like technique under microwave irradiation in which the reaction was carried out in a special reaction vessel made from teflon and capped well to isolate it tightly which insure no leakage of the reaction solvent (see experimental part). 3. Materials and Methods 3.1. General All chemicals including solvents are spectroscopic grade and purchased from Sigma-Aldrich and used without further purification. Cross coupling reactions under microwaves irradiation were carried out in a Milestone microwave Labstation (MicroSYNTH, Touch Control, built-in ASM-45001 magnetic stirrer, Infra-red temperature sensor, and APC-55E automatic pressure control up to 55 bars (800 psi), Italy. Scanning electron microscopy was done using Philips EM 300 SEM, Siemens Autoscan (Germany). Powder X-ray diffraction pattern was measured by Shimadzu Lab-XRD–6000 with CuKα radiation and a secondary monochromator. STARe System thermogravimetric analyzer (TGA) was used to investigate the thermal transformation of the obtained material was investigated under air. Melting points (mp.) were recorded by using a Gallenkamp apparatus. IR (infra-red) spectra have been recorded in KBr discs using Shimadzu FT-IR 3600 FT spectrophotometer. 1 H NMR spectra ligands and complexes have been recorded using Bruker Avance 850 instrument (850 MHz for 1 H, 125 MHz for 13 C) and Varian Mercury VXR-300 NMR spectrometer was used for products in DMSO- d 6 or CDCl 3 . The recorded chemical shifts have been related to that of the used deuterated nmr solvent. 3.2. Organic Synthesis 3.2.1. Synthesis of Ligands: N'-(thiazol-2-yl)-N,N-dimethylformimidamide derivatives (3a-d) A mixture of thiazole-2-amine derivatives 1a-d with N , N -dimethylformamide dimethylacetal ( 2 ) was refluxed for 6 hours using dry benzene as a solvent. The reaction was monitored by TLC at different intervals and when the reaction was complete the reaction mixture was allowed to cool to ambient temperature. The precipitated solid products were separated by vaccum filteration then recrystallized using n -hexane with few drops ethyl acetate to afford an analytically pure crustals of benzothiazole-based formamidine ligands: N'- (thiazol-2-yl)- N,N -dimethylformimidamide (3a-d) The physical and spectroscopic data of ligands 3a,b are illustrated in Table 2 3.2.2. Synthesis of the Pd (II)-complexes 4a-d (precatalysts 4a-d) Sodium tetrachloropalladate was dissolvec in absolute methanol and was added dropwisely to solution of the synthesized thiazole-based ligands 3a,b in methanol and under constant stirring at ambient temperatrue. The orange precipitate of the complexes starts to separate within few minutes and after stirring for 1 h. Filteration of the precipitated complex and washing with distilled water to remove any excess sodium tetrachloropalladate and then thoroughly with methanol. Recrystalization of the synthesized complexes 4a-d was achieved by using ethanol as a recrystallization solvent. The physical and spectroscopic data of complexes 4a-d are illustrated in Table 2 Table 2 Physical and spectroscopic data of ligands 3a,b and precatalysts 4-d Compound No. Yield Mp. (color) IR (KBr) Cm − 1 1 H NMR (CDCl 3 ) 13 C NMR 3a 60% (Brown oil) 1616 (C = N) 1 H NMR-850 Hz (DMSO-d 6 ) δ 3 (s, 3H, N–CH 3 ), 3.14 (s, 3H, N–CH 3 ), 7.13 (dt, J = 8.5 Hz, 1H, Ar-H), 7.28 (dt, J = 8.5 Hz, 1H, Ar-H), 7.55 (d, J = 8.5 Hz, 1H, Ar-H), 7.75 (d, J = 8.5 Hz, 1H, Ar-H), 8.46 (s, 1H, CH) 13 C NMR-850 Hz (DMSO-d 6 ) δ 35.1, 120.3, 121.8, 122.9, 126.1, 133.0, 152.4, 157.6, 173.3. 3b 76% 120 o C (biggie powder) 1637 (C = N) 1 H NMR-850 Hz (DMSO-d 6 ) δ 3.03 (s, 3H, N–CH 3 ), 3.17 (s, 3H, N–CH 3 ), 7.15 (d, J = 8.5 Hz, 1H, Ar-H), 7.55 (d, J = 8.5 Hz, 1H, Ar-H), 7.71 (d, J = 8.5 Hz, 1H, Ar-H), 8.46 (s, 1H, CH) 13 C NMR-850 Hz (DMSO-d 6 ) δ 34.9, 108.5, 113.0, 121.0, 134.0, 149.1, 157.6, 158.0, 173,5. 3c 55% 133 o C (White crystals) 1637 (C = N) 1 H NMR-850 Hz (DMSO-d 6 ) δ 3.03 (s, 3H, N–CH 3 ), 3.17 (s, 3H, N–CH 3 ), 7.15 (d, J = 8.5 Hz, 1H, Ar-H), 7.55 (d, J = 8.5 Hz, 1H, Ar-H), 7.71 (d, J = 8.5 Hz, 1H, Ar-H), 8.46 (s, 1H, CH) 13 C NMR-850 Hz (DMSO-d 6 ) δ 34.9, 108.5, 113.0, 121.0, 134.0, 149.1, 157.6, 158.0, 173,5. 3d 64% 140 o C (White powder ) 1637 (C = N) 1 H NMR-850 Hz (DMSO-d 6 ) δ 3.03 (s, 3H, N–CH 3 ), 3.17 (s, 3H, N–CH 3 ), 7.15 (d, J = 8.5 Hz, 1H, Ar-H), 7.55 (d, J = 8.5 Hz, 1H, Ar-H), 7.71 (d, J = 8.5 Hz, 1H, Ar-H), 8.46 (s, 1H, CH) 13 C NMR-850 Hz (DMSO-d 6 ) δ 34.9, 108.5, 113.0, 121.0, 134.0, 149.1, 157.6, 158.0, 173,5. 4a 59% 205 o C (Light brown powder) 1632 (C = N) 1 H NMR (DMSO- d 6 ) δ 3.03 (s, 3H, CH 3 ), 3.17 (s, 3H, CH 3 )3.18 (s, 6H, 2 CH 3 ), 7.16–7.18 (t, J = 8.5 Hz, 1H), 7.32–7.33 (t, J = 8.5 Hz, 1H), 7.33 (t, J = 8.5 Hz, 1H), 7.50–7.53(t, J = 8.5 Hz, 1H), 7.57–7.58 (d, J = 8.5 Hz, 1H), 7.78–7.79 (d, J = 8.5 Hz, 1H), 7.83–7.85 (dd, J = 8.5 Hz, 1H), and 8.29–8.36 (ddd, J = 59.5 Hz 1H), 8.44–8.51 (d, J = 59.5 Hz, 1H), 8.49 (s, 1H). 13 C NMR (DMSO- d 6 ) δ 35.1, 35.9, 115.8, 120.2, 121.8, 123.0, 126.1, 127.1, 127.6, 133.0 146.5, 146.9 152.6, 157.6, 159.8, 160.9, 172.8, 173.6. 4b 61% 270 o C (Light brown powder) 1627 (C = N) 1 H NMR (DMSO- d 6 ) δ 3.03 (s, 3H, CH 3 ), 3.17 (s, 3H, CH 3 )3.18 (s, 6H, 2 CH 3 ), 7.15–7.18 (td, J = 8.5 Hz, 1H), 7.37–7.39 (td, J = 8.5 Hz, 1H), 7.55–7.57 (dd, J = 8.5 Hz, 1H), 7.71–7.73 (dd, J = 8.5 Hz, 1H), 7.81–7.83 (dd, J = 8.5 Hz, 1H), and 8.27–8.36 (ddd, J = 59.5 Hz 1H), 8.43–8.50 (d, J = 59.5 Hz, 1H), 8.46 (s, 1H). 13 C NMR (DMSO- d 6 ) δ 35.19, 35.89, 108.4, 108.5, 113.8, 113.9, 121.0, 121.4, 134.0, 139.4, 149.1, 150.5, 157.9, 158.1, 159.8, 159.9, 173.4, 175.4. 4c 52% 265 o C (Brown powder) 1627 (C = N) 1 H NMR (DMSO- d 6 ) δ 3.03 (s, 3H, CH 3 ), 3.17 (s, 3H, CH 3 )3.18 (s, 6H, 2 CH 3 ), 7.15–7.18 (td, J = 8.5 Hz, 1H), 7.37–7.39 (td, J = 8.5 Hz, 1H), 7.55–7.57 (dd, J = 8.5 Hz, 1H), 7.71–7.73 (dd, J = 8.5 Hz, 1H), 7.81–7.83 (dd, J = 8.5 Hz, 1H), and 8.27–8.36 (ddd, J = 59.5 Hz 1H), 8.43–8.50 (d, J = 59.5 Hz, 1H), 8.46 (s, 1H). 13 C NMR (DMSO- d 6 ) δ 35.19, 35.89, 108.4, 108.5, 113.8, 113.9, 121.0, 121.4, 134.0, 139.4, 149.1, 150.5, 157.9, 158.1, 159.8, 159.9, 173.4, 175.4. 4d 67% 275 o C (Orange powder) 1627 (C = N) 1 H NMR (DMSO- d 6 ) δ 3.03 (s, 3H, CH 3 ), 3.17 (s, 3H, CH 3 )3.18 (s, 6H, 2 CH 3 ), 7.15–7.18 (td, J = 8.5 Hz, 1H), 7.37–7.39 (td, J = 8.5 Hz, 1H), 7.55–7.57 (dd, J = 8.5 Hz, 1H), 7.71–7.73 (dd, J = 8.5 Hz, 1H), 7.81–7.83 (dd, J = 8.5 Hz, 1H), and 8.27–8.36 (ddd, J = 59.5 Hz 1H), 8.43–8.50 (d, J = 59.5 Hz, 1H), 8.46 (s, 1H). 13 C NMR (DMSO- d 6 ) δ 35.19, 35.89, 108.4, 108.5, 113.8, 113.9, 121.0, 121.4, 134.0, 139.4, 149.1, 150.5, 157.9, 158.1, 159.8, 159.9, 173.4, 175.4. 3.3. Catalytic Study 3.3.1. Suzuki –Miyaura cross-coupling of phenylboronic acid with 4'-bromoacetophenone 3.3.1.1. Effect of precatalysts 4a-d concentration on Suzuki –Miyaura cross-coupling in water under conventional heating Refluxing a mixture of 4'-bromoacetophenone ( 5 ) (1 mmol), phenylboronic acid ( 6 ) (1.2 mmol), TBAB (0.6 mmol), approperiate palladium complexes 4a-d ( 1,5 mol%), K 2 CO 3 (1 mmol) and 10 mL water for 3h at 100°C with stirring. The reaction was monitored by TLC or by GC at different intervals and when the reaction was complete the reaction mixture was allowed to cool to ambient temperature. Reaction workup was achieved by extraction the reaction product using ethyl acetate(3 x 20 mL), then drying the axtracts using unhydrous sodium sulphate. The organic layer was evporated under vaccum to give 4-acetyl-1,1'-biphenyl as a white solid. Using the same experimental conditions, different mol% of the approperiate palladium precatalysts 4a-d (1, 0.75, 0.5, 0.25) were used and in every run the GC yield was calculted as shown in Table 1 . 4. Conclusions Novel nanosized thiazole-based palladium(II) complexes have been synthesized from easily accesseble starting materials by mild conditions. By investigation of the catalytic efficiency of the developed novel catalyst, it is possible to conclude that the novel phosphine-free thiazole-based palladium (II) complexes are efficient in catalysis of Suzuki-Miyaura Cross-coupling reactions using water as a solvent. The latter conditions fit the demand to describe methodology to access the biaryl derivatives as a green ecofriendly strategy. Declarations Conflict of interest The author declare no conflicts of interest. Funding : This work is funding by Deanship of Research and Graduate Studies at King Khalid University through small group research under grant number RGP1/213/46 Author Contribution Afaf Y.Khormi is the corresponding author responsible for all steps of accomplishing this work. Acknowledgments: The author extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through small group research under grant number RGP1/213/46 References Suzuki A (2002) Cross-coupling reactions via organoboranes. J Organomet Chem 653:83–90 Shibasaki M, Boden CD, Kojima A (1997) The asymmetric Heck reaction. Tetrahedron 53:7371–7395 Len C (2020) Catalysts for Suzuki–Miyaura Coupling Reaction. Catalysts. 10, : 50–52 El-Maiss J, Mohy T, El Dine C-S, Lu I, Karamé A, Kanj K, Polychronopoulou J, Shaya (2020) Recent Advances in Metal-Catalyzed Alkyl–Boron (C (sp3))–C (sp2)) Suzuki-Miyaura Cross-Couplings. 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On the mechanism of formation of homocoupled products in the carbon-carbon cross-coupling reaction catalyzed by palladium complexes containing rigid bidentate nitrogen ligands: evidence for the exchange of organic groups between palladium and the transmetalating reagent. Organometallics 13:1972–1980 Kostas ID, Andreadaki FJ, Kovala-Demertzi D, Prentjas C, Demertzis MA (2005) Suzuki–Miyaura cross-coupling reaction of aryl bromides and chlorides with phenylboronic acid under aerobic conditions catalyzed by palladium complexes with thiosemicarbazone ligands. Tetrahedron lett 46:1967–1970 Tenchiu A-C, Ventouri I-K, Ntasi G, Palles D, Kokotos G, Kovala-Demertzi D, Kostas ID (2015) Synthesis of a palladium complex with a β-d-glucopyranosyl-thiosemicarbazone and its application in the Suzuki–Miyaura coupling of aryl bromides with phenylboronic acid. Inorganica Chim Acta 435:142–146 Lidström P, Tierney J, Wathey B, Westman J (2001) Microwave assisted organic synthesis—a review. Tetrahedron 57:9225–9283 Kappe CO, Stadler A, Dallinger D (2012) Microwaves in organic and medicinal chemistry. Wiley de la Hoz A, Diaz-Ortiz A, Moreno A (2005) Microwaves in organic synthesis. Thermal and non-thermal microwave effects. Chem Soc Rev 34:164–178 Kostas ID, Heropoulos GA, Kovala-Demertzi D, Yadav PN, Jasinski JP, Demertzis MA, Andreadaki FJ, Vo-Thanh G, Petit A, Loupy A (2006) Microwave-promoted Suzuki–Miyaura cross-coupling of aryl halides with phenylboronic acid under aerobic conditions catalyzed by a new palladium complex with a thiosemicarbazone ligand. Tetrahedron lett 47:4403–4407 Salih KS, Baqi Y (2020) Microwave-Assisted Palladium-Catalyzed Cross-Coupling Reactions: Generation of Carbon–Carbon Bond. Catalysts 10:4–13 Khormi AY, Farghaly TA, Shaaban MR (2019) Pyrimidyl formamidine palladium(II) complex as a nanocatalyst for aqueous Suzuki-Miyaura coupling. Heliyon 5:e01367 Dawood KM, Darweesh AF, Shaaban MR, Farag AM (2018) Microwave-promoted Heck and Suzuki coupling reactions of new 3-(5-bromobenzofuranyl)pyrazole in aqueous media. Arkivoc v, : 348–358 Shaaban MR, Farghaly TA, Khormi AY, Farag AM (2019) Recent Advances in Synthesis and Uses of Heterocycles-​based Palladium(II) Complexes as Robust, Stable, and Low-​cost Catalysts for Suzuki- Miyaura Crosscouplings. Curr Org Chem 23(15):1601–1662 Darweesh AF, Shaaban MR, Farag AM, Metz P, Dawood KM (2010) Facile Access to Biaryls and 2-Acetyl-5-arylbenzofurans via Suzuki Coupling in Water under Thermal and Microwave Conditions. Synthesis. (2010): 3163–3173 Shaaban MR, Darweesh AF, Dawood KM, Farag AM (2010) Mizoroki-Heck cross-couplings of 2-acetyl-5-bromobenzofuran and aryl halides under microwave irradiation. Arkivoc x, : 208–225 [Job’s] P, Job (1928) Formation and stability of inorganic complexes in solution. Ann Chim 9:113–203 Holzwarth U, Gibson N (2011) The Scherrer equation versus the'Debye-Scherrer equation'. Nat Nanotechnol 6:534–534 Kumar A, Rao GK, Kumar S, Singh AK (2014) Formation and role of palladium chalcogenide and other species in Suzuki–Miyaura and Heck C-C coupling reactions catalyzed with palladium(II) complexes of organo-chalcogen ligands: realities and speculations. Organometallics 33(12):2921–2943 Kumar A, Rao GK, Singh AK (2012) Organo-chalcogen ligands and their palladium(II)complexes: synthesis to catalytic activity for Heck coupling. RSC Adv 2:12552–12574 Phan NTS, Sluys MVD, Jones CW (2006) On the nature of the active species in palladium catalyzed Mizoroki–Heck and Suzuki–Miyaura couplings–homogeneous or heterogeneous catalysis, a critical review. Adv Synth Catal 348:609–679 Schemes Schemes 1 to 3 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files scheme1.jpg Scheme 1: Preparation of the Formamidinyl thiazole-based ligands 3a-d Scheme2.jpg Scheme 2: Synthesis of the thiazole-based palladium(II) complexes 4a-d Scheme3.jpg Scheme 3 Cross-coupling of 4´-bromoacetophenone (5) with phenylboronic acid (6) using precatalysts 4a-d in water Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7546711","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":516664682,"identity":"cb1cd7a4-e7d4-4c4d-b71c-4430ad619e64","order_by":0,"name":"Afaf Y. Khormi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYFAC5mYQycPPwwbmEaOFEaJFsodULQwGZ4jVwt9+sNng455tMsZnjqVJMFRYJzbwH36AV4vEmcTmxBnPbvOYnW07JsFwJj2xQSLNAL81BxKbD/McAGo5z94mwdh2GKiFAb8W+fMPIVqM+0Fa/gG18B//gFeLwY3E5mSQFgNeoMMYG4BaGHLw22J442Gz4QygFokzx5ItEo6lG7dJ5BTg1SJ3PvmwxIcDt+35e9IMb3yosZbt5z++Aa8WVJAAxGwkqB8Fo2AUjIJRgAMAACnhSBT8V26mAAAAAElFTkSuQmCC","orcid":"","institution":"King Khalid University","correspondingAuthor":true,"prefix":"","firstName":"Afaf","middleName":"Y.","lastName":"Khormi","suffix":""}],"badges":[],"createdAt":"2025-09-05 19:08:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7546711/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7546711/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91621207,"identity":"e1841ff1-a837-4ebe-a34c-f9b10d1345af","added_by":"auto","created_at":"2025-09-18 11:31:58","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":95330,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR of spectra and their interpretation Ligand 3d\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/f1d6461bd85988a58d3e4b14.jpg"},{"id":91621210,"identity":"bfea8b8e-f300-431c-9232-2ee6dd185271","added_by":"auto","created_at":"2025-09-18 11:31:58","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":110428,"visible":true,"origin":"","legend":"\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR spectra and their interpretation of Ligand 3d\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/356b7c341a5ce1379c378a11.jpg"},{"id":91622881,"identity":"e5a8aa82-0a87-4557-8590-85dba1275fb0","added_by":"auto","created_at":"2025-09-18 11:47:58","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":108068,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of coordination of Pd on the \u003csup\u003e1\u003c/sup\u003eH NMR spectra and their interpretation of complex 4d\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/782be6f69d712dde99b6a59d.jpg"},{"id":91622264,"identity":"fcf5e6d0-7f56-4629-947c-25743d2720c4","added_by":"auto","created_at":"2025-09-18 11:39:58","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":67617,"visible":true,"origin":"","legend":"\u003cp\u003eTGA (A) and DTA (B) of the complexes \u003cstrong\u003e4a-d\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/9d147e94a87aec930b7f14bd.jpg"},{"id":91622265,"identity":"ae3d6ecb-24e0-4f5f-9ae7-9fe10e13113d","added_by":"auto","created_at":"2025-09-18 11:39:58","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":194761,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of complex \u003cstrong\u003e4a\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/9320f82b7dce1ef3da329a31.jpg"},{"id":91624056,"identity":"8424809d-4bf6-404e-bab8-3200eaba1a05","added_by":"auto","created_at":"2025-09-18 11:55:58","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":233415,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of complexes \u003cstrong\u003e4b\u003c/strong\u003e and ligand \u003cstrong\u003e3b\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/f307d0528a84cc5a2ce49714.jpg"},{"id":91624055,"identity":"36c42b3f-a847-495b-a957-ebca8336a0e9","added_by":"auto","created_at":"2025-09-18 11:55:58","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":175670,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of complexes \u003cstrong\u003e4c\u003c/strong\u003e and ligand \u003cstrong\u003e3c\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/ba91d9d2f64fb741d3bb769a.jpg"},{"id":91621216,"identity":"12392946-aa0d-498b-8f50-e84a70a82b7d","added_by":"auto","created_at":"2025-09-18 11:31:58","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":155867,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of complexes \u003cstrong\u003e4d\u003c/strong\u003e and ligand \u003cstrong\u003e3d\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/0d6eb76f843eb92ffd238694.jpg"},{"id":91621220,"identity":"a326649b-acea-4862-90b0-8a04e89b77ef","added_by":"auto","created_at":"2025-09-18 11:31:58","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":114797,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray Diffraction Analysis of complexes 4a-d\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/b167bd75b08f4ec3ff0b37e0.jpg"},{"id":93017677,"identity":"2c20190d-1216-4d36-995d-692aa5ba93eb","added_by":"auto","created_at":"2025-10-08 08:17:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2375135,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/bd197c93-1ede-4f4b-abde-8faacf66792d.pdf"},{"id":91622263,"identity":"d4473325-642d-4336-996c-a039e73d5174","added_by":"auto","created_at":"2025-09-18 11:39:58","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":44394,"visible":true,"origin":"","legend":"\u003cp\u003eScheme 1: Preparation of the Formamidinyl thiazole-based ligands 3a-d\u003c/p\u003e","description":"","filename":"scheme1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/7cba276c5068c221b6d7312a.jpg"},{"id":91621209,"identity":"4c07bd72-bfbe-4527-af0a-4c12a2398674","added_by":"auto","created_at":"2025-09-18 11:31:58","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":34512,"visible":true,"origin":"","legend":"\u003cp\u003eScheme 2: Synthesis of the thiazole-based palladium(II) complexes 4a-d\u003c/p\u003e","description":"","filename":"Scheme2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/3599f8d2ee08fa8ef4789231.jpg"},{"id":91621211,"identity":"eea26a86-cfce-4a85-bfd7-5e260323e40b","added_by":"auto","created_at":"2025-09-18 11:31:58","extension":"jpg","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":57490,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 3\u003c/strong\u003e Cross-coupling of 4´-bromoacetophenone (\u003cstrong\u003e5\u003c/strong\u003e) with phenylboronic acid (\u003cstrong\u003e6\u003c/strong\u003e) using precatalysts \u003cstrong\u003e4a-d\u003c/strong\u003e in water\u003c/p\u003e","description":"","filename":"Scheme3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7546711/v1/0dbdd1b1231c95b58a420372.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Formamidinyl Thiazole-Based Palladium Complexes as Efficient Nano-sized Catalysts for Aqueous Suzuki –Miyaura Cross-Couplings","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOne of the versatile applications of the palladium complexes their exhibitions in the C-C cross-coupling reactions. These complexes are characterized by high stability and unique reactivity, which depends on the identity of the ligand and the mode of coordination of such ligands to the core palladium atom. Nitrogen containing heterocyclic ligands were usually considered in fitting that demand in the palladium coordination and usually their complexes sound well in the various applications of organic transformations. On the other hand, Suzuki-Miyaura cross-coupling (SMC) reaction is a crucial tool in organic transformation to access a biaryls derivatives with great selectivity and using soft conditions. Biaryls derivatives constitute an essential part in diverse natural products and many pharmaceuticals. In this context, palladium complexes containing a heterocyclic ligand have been used as efficient pre-catalysts for homogenous Suzuki-Miyaura cross-coupling under mild reaction conditions. [1\u0026ndash;20]\u003c/p\u003e\u003cp\u003eAs an aim to our research program, I'm focusing on the use of water as a green solvent to perform the C-C coupling reactions using heterocyclic ligands-based palladium complexes as catalytic precursors, recently i have explored the use of such complexes to catalyse the Suzuki-Miyaura cross-coupling reaction with very excellent outcomes in aqueous media [20\u0026ndash;25] On continuing our efforts in the synthesis and catalytic applications of novel complexes, I envisioned the synthesis of new ligands combining a formamidine functionality with a thiazole ring. This 5-membered heterocyclic fragment together with the formamidine moiety can behave as strong N-donors in the developed ligands [26\u0026ndash;28]. I believe that this structural combination could provide a targeted stability to the palladium complex formed as well as a better tuning of its catalytic efficiency. I also describe the catalytic applications of these complexes in Suzuki-Miyaura cross-coupling reaction in water.\u003c/p\u003e"},{"header":"2. Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Synthesis of the benzothiazole-based Pd(II) complexes 4a,b\u003c/h2\u003e\u003cp\u003eCondensation of 2-aminothiazole derivatives (\u003cb\u003e1a-d)\u003c/b\u003e with \u003cem\u003eN\u003c/em\u003e,\u003cem\u003eN\u003c/em\u003e-dimethylformamide dimethylacetal (DMF DMA) (\u003cb\u003e2\u003c/b\u003e) furnished the corresponding 2-formamidinylthiazole derivatives (\u003cb\u003e3a-d\u003c/b\u003e) as depicted in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The structural elucidation of 2-formamidinylthiazole \u003cb\u003e3a-d\u003c/b\u003e was achieved by using spectroscopic data and elemental analyses. All the \u003csup\u003e1\u003c/sup\u003eH NMR spectra of the synthesized ligands \u003cb\u003e3a-d\u003c/b\u003e showed two singlet signals of the two magnetically nonequivalent methyl groups of N(\u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eMe\u003c/span\u003e)\u003csub\u003e2\u003c/sub\u003e group in the region of \u003cem\u003eδ\u003c/em\u003e 2.98 and 3.14 ppm. In addition, the formamidine group proton (-N\u0026thinsp;=\u0026thinsp;C\u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eH\u003c/span\u003e-) resonates as a singlet in the region of \u003cem\u003eδ\u003c/em\u003e 8.27\u0026ndash;8.45 ppm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor instance, the \u003csup\u003e1\u003c/sup\u003eH NMR spectrum of the synthesized ligands \u003cb\u003e3d\u003c/b\u003e revealed two singlet signals of the two methyl protons of N(\u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eMe\u003c/span\u003e)\u003csub\u003e2\u003c/sub\u003e group in the region of \u003cem\u003eδ\u003c/em\u003e 2.99 and 3.13 ppm. The aromatic protons appear as two doublets at \u003cem\u003eδ\u003c/em\u003e 7.44 and 7.90. In addition. a singlet signal at \u003cem\u003eδ\u003c/em\u003e 7.49 assigned for the thiazole CH proton and the formamidine group proton (-N\u0026thinsp;=\u0026thinsp;C\u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eH\u003c/span\u003e-) resonates as a singlet in the region of \u003cem\u003eδ\u003c/em\u003e 8.36 ppm. \u003csup\u003e13\u003c/sup\u003eC NMR spectra of the same ligand \u003cb\u003e3d\u003c/b\u003e showed the characteristic nonequivalent 10 carbon atoms resonance at their expected chemical shifts as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Also the \u003csup\u003e13\u003c/sup\u003eC NMR spectra prove the magnetic nonequivalence of the two methyl groups of the N(\u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003eMe\u003c/span\u003e)\u003csub\u003e2\u003c/sub\u003e group. Considering the IR spectra of the synthesized ligands \u003cb\u003e3a-d\u003c/b\u003e, all ligands spectra revealed the presence of C\u0026thinsp;=\u0026thinsp;N group absorption band at the expected frequency near 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (see experimental part).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThiazole-based palladium complexes \u003cb\u003e4a-d\u003c/b\u003e could be accessed by addition of methanolic sodium tetrachloropalladate solution to equimolar amount of formamidinylthiazole ligands \u003cb\u003e3a-d\u003c/b\u003e dissolved in methanol at ambient temperature. Immediate precipitates of the targeted complexes were formed and after complete addition of sodium palladate solution good yields of the corresponding thiazole-based palladium(II) complexes \u003cb\u003e4a-d\u003c/b\u003e were obtained as shown in Scheme \u003cspan refid=\"Sch2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe structural proof of synthesized thiazole-Pd complexes \u003cb\u003e4a-d\u003c/b\u003e was based on the spectroscopic analysis and physical characteristics. \u003csup\u003e1\u003c/sup\u003eH NMR spectrum of \u003cb\u003e4d\u003c/b\u003e (taken as an example) revealed the presence of two singlet signals at \u003cem\u003eδ\u003c/em\u003e 3.02 and 3.16 ppm due to the protons of \u003cem\u003eN(Me)\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e group. In addition to two doublets signals at \u003cem\u003eδ\u003c/em\u003e 7.46, and 7.91 ppm with \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz assigned to the two aromatic rings (CH) protons at position 5 and 6 in each phenyl thiazole moiety and two singlet signals at \u003cem\u003eδ\u003c/em\u003e 7.54 and 8.44 ppm due the thiazole ring proton and the formamidine moiety proton, respectively. From the values of the chemical shift \u003cem\u003eδ\u003c/em\u003e the coordination of the pallidum atom to the ligand molecules caused a general increase in the values of the chemical shifts \u003cem\u003eδ\u003c/em\u003e of all protons of the ligand molecule as shown in the comparison Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Thermogravimetric analysis TGA/DTA\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eTGA (thermogravimetric Analysis) and DTA (differential thermal analysis) were performed for the four palladium complexes \u003cb\u003e4a-d\u003c/b\u003e to investigate their thermal stability. TGA and DTA analysis were performed under nitrogen flow, in temperature range from ambient (25\u0026deg;C) up to 800\u0026deg;C, with a heating rate of 10\u0026deg;C/min. The obtained TG and DTA thermograms for are shown in Fig. (A) and (B), respectively. All complexes exhibited a similar thermal decomposition behavior, with a high thermal stability up to ~\u0026thinsp;250\u0026deg;C for \u003cb\u003e4b-d\u003c/b\u003e and around 225 for complex \u003cb\u003e4a\u003c/b\u003e. The weight loss observed in TGA curves below ~\u0026thinsp;250\u0026deg;C and ~\u0026thinsp;225\u0026deg;C for samples \u003cb\u003e4b-d\u003c/b\u003e and for sample \u003cb\u003e4a\u003c/b\u003e, respectively, is attributed to the physically adsorbed water and solvent. This weight loss was around 2% for samples \u003cb\u003e4b-d\u003c/b\u003e and around 4.5% for sample \u003cb\u003e4a\u003c/b\u003e. This was clearly observed in \u003cb\u003e4a\u003c/b\u003e DTA curve by an exothermic peak with a maximum at around 140\u0026deg;C. The main weight loss was observed between ~\u0026thinsp;225 and ~\u0026thinsp;400\u0026deg;C for all samples which attributed to the decomposition of the ligands. This decomposition of the organic matter was observed in DTA curves by endothermic peaks with maximums at ~\u0026thinsp;285\u0026deg;C and ~\u0026thinsp;275\u0026deg;C for samples \u003cb\u003e4b, d\u003c/b\u003e and \u003cb\u003e4a, c\u003c/b\u003e, respectively. This is corresponding to a weigh loss of 41.54%, 44.6%, 42.33%, and 46.37% for samples \u003cb\u003e4a-d\u003c/b\u003e, respectively.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. The scanning electron microscopy (SEM)\u003c/h2\u003e\u003cp\u003eThe morphology of solid ligands \u003cb\u003e3b-d\u003c/b\u003e and their palladium complexes \u003cb\u003e4a-d\u003c/b\u003e was investigated by scanning electron microscopy (SEM). The obtained micrographs are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The SEM images of the complex \u003cb\u003e4a\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-c) depicted spherical and uniform particles, with size in the range of 0.94\u0026ndash;3.96 \u0026micro;m. The particles size distribution was narrow at around 1.58 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). The obtained micrographs of the ligand \u003cb\u003e3b\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee, f) revealed the formation of particles with irregular shape and particles diameter ranges from 0.15 \u0026micro;m to 30 \u0026micro;m. After the complexation of the ligand \u003cb\u003e3b\u003c/b\u003e with palladium, the SEM images of the obtained complex \u003cb\u003e4b\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg, h) showed the formation of flower-like microspheres with diameter ranges from 0.4 \u0026micro;m to 10.05 \u0026micro;m, and average diameter of 5.58 \u0026micro;m. These flower-like microspheres were formed by rectangular nanoparticles oriented toward the microsphere center (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ei), with average length of 3 \u0026micro;m, width average of 0.3 \u0026micro;m, and thickness of around 90 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ej). SEM images of ligand \u003cb\u003e3c\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ek, l) showed the formation of thin micro platelets with irregular shape, and size ranges from 1 to 70 \u0026micro;m, with platelets average thickness of around 2.5 \u0026micro;m. After the complexation of this ligand with palladium (\u003cb\u003e4c\u003c/b\u003e), the particles shape and size were completely transformed to microspheres (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003em, n) with particles size ranges from 1.83 to 9.77 \u0026micro;m, average diameter of 6.08 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eo). The further enlargement of \u003cb\u003e4c\u003c/b\u003e SEM micrographs revealed that these microspheres are formed by worm-like nanoparticles with length ranges from 50 to 500 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ep). However, the SEM micrographs of the ligand \u003cb\u003e3d\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eq, r) depicted the formation of micro-rectangles with diameter ranges from 5 to 100 \u0026micro;m, and thickness of around 2.5 \u0026micro;m. The SEM images of the corresponding palladium complex \u003cb\u003e4d\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003es-u) revealed the formation of microparticles with irregular shape. The study of the particles size distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ev) showed that the particles size ranges from 60 nm to 7.38 \u0026micro;m, and average diameter of 2.15 \u0026micro;m.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Powder X-ray Diffraction Analysis\u003c/h2\u003e\u003cp\u003eThe powder XRD analysis were performed to investigate the crystallinity of the obtained complexes \u003cb\u003e4a-d\u003c/b\u003e. The obtained results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The XRD pattern of complex 4a does not presents any reflections. This is indicating an amorphous structure of this complex. However, the XRD patterns of complexes \u003cb\u003e4b\u003c/b\u003e and \u003cb\u003e4c\u003c/b\u003e recorded three similar main reflections at 2Ɵ = 7.3\u0026ordm;, 15.0\u0026ordm;, and 26.5\u0026ordm;, indicating the existence of crystalline phases. Complex \u003cb\u003e4d\u003c/b\u003e also presents three main reflections at 2Ɵ = 14.6\u0026ordm;, 21.3\u0026ordm;, and 27.0\u0026ordm;, but are different than those observed for complexes \u003cb\u003e4b\u003c/b\u003e and \u003cb\u003e4c\u003c/b\u003e, and less sharp. Suggesting the existence of a crystalline phase in \u003cb\u003e4d\u003c/b\u003e structure.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Catalytic efficiency of complex 4a-d in Suzuki \u0026ndash;Miyaura Cross-Couplings\u003c/h2\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e2.5.1. Effect of concentration of the complex 4a,b in catalysis of Suzuki \u0026ndash;Miyaura Cross-Couplings\u003c/h2\u003e\u003cp\u003eIn a systematic study when developing a new catalytic system an investigation of the catalytic efficiency of this system begins with study the concentration limits that affords the high efficiency of the target catalytic system in the mentioned catalysed reaction. Thus, the catalytic efficiency of the developed precatalysts based on the synthesized thiazole-based palladium complexes in C-C cross coupling reaction, have been studied by investigating the concentration effect of the thiazole-based palladium complexes \u003cb\u003e4a-d\u003c/b\u003e on Suzuki\u0026ndash;Miyaura Cross-Couplings between \u003cem\u003ep\u003c/em\u003e-bromoacetophenone (\u003cb\u003e5\u003c/b\u003e), as a halide component and phenyl boronic acid (\u003cb\u003e6\u003c/b\u003e) as depicted in scheme \u003cspan refid=\"Sch3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Thus, the C-C cross-coupling reaction proceeded in water as a solvent and presence of a mild base, K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and in the presence of a phase transfer agent, namely tetrabutylammonium bromide (TBAB) as a co-catalyst for the aqueous Suzuki\u0026ndash;Miyaura Cross-Couplings under conventional heating conditions. Therefore, performing the cross-coupling reaction in the presence of different concentrations of the the thiazole-based palladium complexes \u003cb\u003e4a-d\u003c/b\u003e with furnished 4-acetyl-1,1\u0026acute;-biphenyl (\u003cb\u003e7\u003c/b\u003e) as the desired cross coupled product, Following up the reaction by TLC showed that, three hours of thermal heating was enough time to access 4-acetyl-1,1\u0026acute;-biphenyl (\u003cb\u003e7\u003c/b\u003e) as illustrated in Scheme \u003cspan refid=\"Sch3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, starting with 1.5 mol% of the appropriate thiazole-based palladium precatalyst \u003cb\u003e4a-d\u003c/b\u003e to catalyse the C-C cross coupling and the molar ratio of \u003cem\u003ep\u003c/em\u003e-bromoacetophenone (\u003cb\u003e5\u003c/b\u003e): phenyl boronic acid (\u003cb\u003e6\u003c/b\u003e): K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e: TBAB was 1.0/1.2/1.0 / 0.6, we got 100% conversion with complete disappearance of the starting materials (measured by GC-analysis) and the cross coupled product 4-acetyl-1,1\u0026acute;-biphenyl (\u003cb\u003e7\u003c/b\u003e) was obtained (entry 1, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). By gradual decrease in the amount of the used thiazole-based palladium precatalyst \u003cb\u003e4a-d\u003c/b\u003e (from 1.5 to 0.25 mol%), we noticed that a full to excellent GC-conversion using the same cross coupling conditions (entries 2\u0026ndash;5, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Thus, thiazole-based palladium precatalyst \u003cb\u003e4a-d\u003c/b\u003e showed similar excellent catalytic efficiency in the C-C cross coupling reaction even when using very low mol% and regardless the nature of the substituent in the thiazole ring. When Suzuki\u0026ndash;Miyaura reaction was carried out in absence of thiazole-based palladium precatalyst \u003cb\u003e4a-d\u003c/b\u003e, the starting \u003cem\u003ep\u003c/em\u003e-bromoacetophenone (\u003cb\u003e5\u003c/b\u003e) was completely recovered from the reaction mixture as expected as showed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, entry 6. The obtained cross coupled product was analyzed and its structure was confirmed by spectroscopic tools.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eEffect of concentration of precatlyst \u003cb\u003e4a-d\u003c/b\u003e on the coupling of 4\u0026acute;-bromoacetophenone (\u003cb\u003e5\u003c/b\u003e) with phenylboronic acid (\u003cb\u003e6\u003c/b\u003e) in water.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eEntry\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ePd, mol%%\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eGC Conversion%\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePrecatalyst \u003cb\u003e4a\u003c/b\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePrecatalyst \u003cb\u003e4b\u003c/b\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePrecatalyst \u003cb\u003e4c\u003c/b\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ePrecatalyst \u003cb\u003e4d\u003c/b\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e91\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e88\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e95\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e91\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e88\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e Conditions: 4\u0026acute;-bromoacetophenone (\u003cb\u003e5\u003c/b\u003e) / phenylboronic acid (\u003cb\u003e6\u003c/b\u003e)/ K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e/ TBAB / water: 1.0/1.2/1.0 / 0.6/ 10 mL, under thermal heating at 100\u0026deg;C for 3\u0026nbsp;h. \u003csup\u003eb\u003c/sup\u003e Conversions were based on GC-analysis: the conversion was monitored by Shimadzu GC-17A gas chromatography (GC), equipped with flam ionization detector and RTX-5 column, 30 m x 0.25 mm, 1 \u0026micro;m film thickness. Helium was used as carrier gas at flow rate 0.6 mL/min. Samples were withdrawn from the reaction mixture periodically. \u0026nbsp;Injection volume was 1 \u0026micro;l, and total flow was 100 ml/min. Oven temperature was initiated at 100\u0026deg;C for 2 min up to 130\u0026deg;C at a rate of 15\u0026deg;C/ min held for 2 min, then increased to 150\u0026deg;C at a rate of 2\u0026deg;C/ min held for 2 min. The Injector temperature was 160\u0026deg;C and the detector temperature was 200\u0026deg;C.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn order to explain how the palladium precatalyst 4 take part in the catalytic process of the reaction does, it was suggested that the complex acts as \u0026ldquo;dormant species\u0026rdquo; and does not participate in the reaction catalytic cycle in an actual manner. the precatalyst \u003cb\u003e4\u003c/b\u003e is considered as the main precursor for the palladium catalytically active species, thus it is considered as a precatalyst in the cross-coupling reaction. Generally, the palladium (0) species were the true active catalysts as reported previously [29.30]. Therefore, the precatalyst \u003cb\u003e4\u003c/b\u003e may serve as a reservoir that is indirectly involved in the catalytic cycle of the cross coupling and it is the main source of release of nano-sized palladium(0) which can afford catalytic role even when used with very low concentrations [31]. As an alternative green methodology for the present cross coupling reaction we have used a hydrothermal like technique under microwave irradiation in which the reaction was carried out in a special reaction vessel made from teflon and capped well to isolate it tightly which insure no leakage of the reaction solvent (see experimental part).\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Materials and Methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.1. General\u003c/h2\u003e\u003cp\u003eAll chemicals including solvents are spectroscopic grade and purchased from Sigma-Aldrich and used without further purification. Cross coupling reactions under microwaves irradiation were carried out in a Milestone microwave Labstation (MicroSYNTH, Touch Control, built-in ASM-45001 magnetic stirrer, Infra-red temperature sensor, and APC-55E automatic pressure control up to 55 bars (800 psi), Italy. Scanning electron microscopy was done using Philips EM 300 SEM, Siemens Autoscan (Germany). Powder X-ray diffraction pattern was measured by Shimadzu Lab-XRD\u0026ndash;6000 with CuKα radiation and a secondary monochromator. STARe System thermogravimetric analyzer (TGA) was used to investigate the thermal transformation of the obtained material was investigated under air. Melting points (mp.) were recorded by using a Gallenkamp apparatus. IR (infra-red) spectra have been recorded in KBr discs using Shimadzu FT-IR 3600 FT spectrophotometer. \u003csup\u003e1\u003c/sup\u003eH NMR spectra ligands and complexes have been recorded using Bruker Avance 850 instrument (850 MHz for \u003csup\u003e1\u003c/sup\u003eH, 125 MHz for \u003csup\u003e13\u003c/sup\u003eC) and Varian Mercury VXR-300 NMR spectrometer was used for products in DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e or CDCl\u003csub\u003e3\u003c/sub\u003e. The recorded chemical shifts have been related to that of the used deuterated nmr solvent.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Organic Synthesis\u003c/h2\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1. Synthesis of Ligands: \u003cem\u003eN'-(thiazol-2-yl)-N,N-dimethylformimidamide derivatives\u003c/em\u003e (3a-d)\u003c/h2\u003e\u003cp\u003eA mixture of thiazole-2-amine derivatives \u003cb\u003e1a-d\u003c/b\u003e with \u003cem\u003eN\u003c/em\u003e,\u003cem\u003eN\u003c/em\u003e-dimethylformamide dimethylacetal (\u003cb\u003e2\u003c/b\u003e) was refluxed for 6 hours using dry benzene as a solvent. The reaction was monitored by TLC at different intervals and when the reaction was complete the reaction mixture was allowed to cool to ambient temperature. The precipitated solid products were separated by vaccum filteration then recrystallized using \u003cem\u003en\u003c/em\u003e-hexane with few drops ethyl acetate to afford an analytically pure crustals of benzothiazole-based formamidine ligands: \u003cem\u003eN'-\u003c/em\u003e(thiazol-2-yl)-\u003cem\u003eN,N\u003c/em\u003e-dimethylformimidamide \u003cb\u003e(3a-d)\u003c/b\u003e The physical and spectroscopic data of ligands \u003cb\u003e3a,b\u003c/b\u003e are illustrated in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2. Synthesis of the Pd (II)-complexes 4a-d (precatalysts 4a-d)\u003c/h2\u003e\u003cp\u003eSodium tetrachloropalladate was dissolvec in absolute methanol and was added dropwisely to solution of the synthesized thiazole-based ligands \u003cb\u003e3a,b\u003c/b\u003e in methanol and under constant stirring at ambient temperatrue. The orange precipitate of the complexes starts to separate within few minutes and after stirring for 1 h. Filteration of the precipitated complex and washing with distilled water to remove any excess sodium tetrachloropalladate and then thoroughly with methanol. Recrystalization of the synthesized complexes \u003cb\u003e4a-d\u003c/b\u003e was achieved by using ethanol as a recrystallization solvent. The physical and spectroscopic data of complexes \u003cb\u003e4a-d\u003c/b\u003e are illustrated in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePhysical and spectroscopic data of ligands \u003cb\u003e3a,b\u003c/b\u003e and precatalysts \u003cb\u003e4-d\u003c/b\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCompound No.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eYield\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMp.\u003c/p\u003e\u003cp\u003e(color)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eIR (KBr)\u003c/p\u003e\u003cp\u003eCm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR (CDCl\u003csub\u003e3\u003c/sub\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e3a\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e60%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e(Brown oil)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1616 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) δ 3 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 3.14 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 7.13 (dt, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.28 (dt, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.55 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.75 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 8.46 (s, 1H, CH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 35.1, 120.3, 121.8, 122.9, 126.1, 133.0, 152.4, 157.6, 173.3.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e3b\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e76%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e120 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\u003cp\u003e(biggie powder)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1637 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) δ 3.03 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 3.17 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 7.15 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.55 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.71 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 8.46 (s, 1H, CH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 34.9, 108.5, 113.0, 121.0, 134.0, 149.1, 157.6, 158.0, 173,5.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e3c\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e55%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e133 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\u003cp\u003e(White crystals)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1637 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) δ 3.03 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 3.17 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 7.15 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.55 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.71 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 8.46 (s, 1H, CH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 34.9, 108.5, 113.0, 121.0, 134.0, 149.1, 157.6, 158.0, 173,5.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e3d\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e64%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e140 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\u003cp\u003e(White powder )\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1637 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) δ 3.03 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 3.17 (s, 3H, N\u0026ndash;CH\u003csub\u003e3\u003c/sub\u003e), 7.15 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.55 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 7.71 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5\u0026nbsp;Hz, 1H, Ar-H), 8.46 (s, 1H, CH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR-850 Hz (DMSO-d\u003csub\u003e6\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 34.9, 108.5, 113.0, 121.0, 134.0, 149.1, 157.6, 158.0, 173,5.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e4a\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e59%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e205 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\u003cp\u003e(Light brown powder)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1632 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 3.03 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e), 3.17 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e)3.18 (s, 6H, 2 CH\u003csub\u003e3\u003c/sub\u003e), 7.16\u0026ndash;7.18 (t, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.32\u0026ndash;7.33 (t, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.33 (t, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.50\u0026ndash;7.53(t, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.57\u0026ndash;7.58 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.78\u0026ndash;7.79 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.83\u0026ndash;7.85 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), and 8.29\u0026ndash;8.36 (ddd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz 1H), 8.44\u0026ndash;8.51 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz, 1H), 8.49 (s, 1H).\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 35.1, 35.9, 115.8, 120.2, 121.8, 123.0, 126.1, 127.1, 127.6, 133.0 146.5, 146.9 152.6, 157.6, 159.8, 160.9, 172.8, 173.6.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e4b\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e61%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e270 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\u003cp\u003e(Light brown powder)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1627 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 3.03 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e), 3.17 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e)3.18 (s, 6H, 2 CH\u003csub\u003e3\u003c/sub\u003e), 7.15\u0026ndash;7.18 (td, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.37\u0026ndash;7.39 (td, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.55\u0026ndash;7.57 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.71\u0026ndash;7.73 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.81\u0026ndash;7.83 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), and 8.27\u0026ndash;8.36 (ddd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz 1H), 8.43\u0026ndash;8.50 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz, 1H), 8.46 (s, 1H).\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 35.19, 35.89, 108.4, 108.5, 113.8, 113.9, 121.0, 121.4, 134.0, 139.4, 149.1, 150.5, 157.9, 158.1, 159.8, 159.9, 173.4, 175.4.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e4c\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e52%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e265 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\u003cp\u003e(Brown powder)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1627 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 3.03 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e), 3.17 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e)3.18 (s, 6H, 2 CH\u003csub\u003e3\u003c/sub\u003e), 7.15\u0026ndash;7.18 (td, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.37\u0026ndash;7.39 (td, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.55\u0026ndash;7.57 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.71\u0026ndash;7.73 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.81\u0026ndash;7.83 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), and 8.27\u0026ndash;8.36 (ddd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz 1H), 8.43\u0026ndash;8.50 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz, 1H), 8.46 (s, 1H).\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 35.19, 35.89, 108.4, 108.5, 113.8, 113.9, 121.0, 121.4, 134.0, 139.4, 149.1, 150.5, 157.9, 158.1, 159.8, 159.9, 173.4, 175.4.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003e4d\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e67%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e275 \u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\u003cp\u003e(Orange powder)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1627 (C\u0026thinsp;=\u0026thinsp;N)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 3.03 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e), 3.17 (s, 3H, CH\u003csub\u003e3\u003c/sub\u003e)3.18 (s, 6H, 2 CH\u003csub\u003e3\u003c/sub\u003e), 7.15\u0026ndash;7.18 (td, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.37\u0026ndash;7.39 (td, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.55\u0026ndash;7.57 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.71\u0026ndash;7.73 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), 7.81\u0026ndash;7.83 (dd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8.5 Hz, 1H), and 8.27\u0026ndash;8.36 (ddd, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz 1H), 8.43\u0026ndash;8.50 (d, \u003cem\u003eJ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;59.5 Hz, 1H), 8.46 (s, 1H).\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC NMR (DMSO-\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e6\u003c/em\u003e\u003c/sub\u003e) \u003cem\u003eδ\u003c/em\u003e 35.19, 35.89, 108.4, 108.5, 113.8, 113.9, 121.0, 121.4, 134.0, 139.4, 149.1, 150.5, 157.9, 158.1, 159.8, 159.9, 173.4, 175.4.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Catalytic Study\u003c/h2\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003ch2\u003e3.3.1. Suzuki \u0026ndash;Miyaura cross-coupling of phenylboronic acid with 4'-bromoacetophenone\u003c/h2\u003e\u003cdiv id=\"Sec16\" class=\"Section4\"\u003e\u003ch2\u003e3.3.1.1. Effect of precatalysts 4a-d concentration on Suzuki \u0026ndash;Miyaura cross-coupling in water under conventional heating\u003c/h2\u003e\u003cp\u003eRefluxing a mixture of 4'-bromoacetophenone (\u003cb\u003e5\u003c/b\u003e) (1 mmol), phenylboronic acid (\u003cb\u003e6\u003c/b\u003e) (1.2 mmol), TBAB (0.6 mmol), approperiate palladium complexes \u003cb\u003e4a-d\u003c/b\u003e ( 1,5 mol%), K\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (1 mmol) and 10 mL water for 3h at 100\u0026deg;C with stirring. The reaction was monitored by TLC or by GC at different intervals and when the reaction was complete the reaction mixture was allowed to cool to ambient temperature. Reaction workup was achieved by extraction the reaction product using ethyl acetate(3 x 20 mL), then drying the axtracts using unhydrous sodium sulphate. The organic layer was evporated under vaccum to give 4-acetyl-1,1'-biphenyl as a white solid. Using the same experimental conditions, different mol% of the approperiate palladium precatalysts \u003cb\u003e4a-d\u003c/b\u003e (1, 0.75, 0.5, 0.25) were used and in every run the GC yield was calculted as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eNovel nanosized thiazole-based palladium(II) complexes have been synthesized from easily accesseble starting materials by mild conditions. By investigation of the catalytic efficiency of the developed novel catalyst, it is possible to conclude that the novel phosphine-free thiazole-based palladium (II) complexes are efficient in catalysis of Suzuki-Miyaura Cross-coupling reactions using water as a solvent. The latter conditions fit the demand to describe methodology to access the biaryl derivatives as a green ecofriendly strategy.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003cp\u003eThe author declare no conflicts of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding :\u003c/h2\u003e\u003cp\u003eThis work is funding by Deanship of Research and Graduate Studies at King Khalid University through small group research under grant number RGP1/213/46\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAfaf Y.Khormi is the corresponding author responsible for all steps of accomplishing this work.\u003c/p\u003e\u003ch2\u003eAcknowledgments:\u003c/h2\u003e\u003cp\u003eThe author extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through small group research under grant number RGP1/213/46\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSuzuki A (2002) Cross-coupling reactions via organoboranes. 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Nat Protoc 2:2930\u0026ndash;2944\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZim D, Gruber AS, Ebeling G, Dupont J, Monteiro AL (2000) Sulfur-containing palladacycles: Efficient Phosphine-free catalyst precursors for the Suzuki cross-coupling reaction at room temperature. Org Lett 2:2881\u0026ndash;2884\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBotella L, N\u0026aacute;jera C (2002) Convenient Oxime-Carbapalladacycle‐Catalyzed Suzuki Cross‐Coupling of Aryl Chlorides in Water. Angew Chem Int Ed 41:179\u0026ndash;181\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYang D, Chen Y-C, Zhu N-Y (2004) Sterically bulky thioureas as air-and moisture-stable ligands for Pd-catalyzed Heck reactions of aryl halides. 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Organometallics 13:1972\u0026ndash;1980\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKostas ID, Andreadaki FJ, Kovala-Demertzi D, Prentjas C, Demertzis MA (2005) Suzuki\u0026ndash;Miyaura cross-coupling reaction of aryl bromides and chlorides with phenylboronic acid under aerobic conditions catalyzed by palladium complexes with thiosemicarbazone ligands. Tetrahedron lett 46:1967\u0026ndash;1970\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTenchiu A-C, Ventouri I-K, Ntasi G, Palles D, Kokotos G, Kovala-Demertzi D, Kostas ID (2015) Synthesis of a palladium complex with a β-d-glucopyranosyl-thiosemicarbazone and its application in the Suzuki\u0026ndash;Miyaura coupling of aryl bromides with phenylboronic acid. Inorganica Chim Acta 435:142\u0026ndash;146\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLidstr\u0026ouml;m P, Tierney J, Wathey B, Westman J (2001) Microwave assisted organic synthesis\u0026mdash;a review. 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Tetrahedron lett 47:4403\u0026ndash;4407\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSalih KS, Baqi Y (2020) Microwave-Assisted Palladium-Catalyzed Cross-Coupling Reactions: Generation of Carbon\u0026ndash;Carbon Bond. Catalysts 10:4\u0026ndash;13\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKhormi AY, Farghaly TA, Shaaban MR (2019) Pyrimidyl formamidine palladium(II) complex as a nanocatalyst for aqueous Suzuki-Miyaura coupling. Heliyon 5:e01367\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDawood KM, Darweesh AF, Shaaban MR, Farag AM (2018) Microwave-promoted Heck and Suzuki coupling reactions of new 3-(5-bromobenzofuranyl)pyrazole in aqueous media. Arkivoc v, : 348\u0026ndash;358\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShaaban MR, Farghaly TA, Khormi AY, Farag AM (2019) Recent Advances in Synthesis and Uses of Heterocycles-​based Palladium(II) Complexes as Robust, Stable, and Low-​cost Catalysts for Suzuki- Miyaura Crosscouplings. Curr Org Chem 23(15):1601\u0026ndash;1662\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDarweesh AF, Shaaban MR, Farag AM, Metz P, Dawood KM (2010) Facile Access to Biaryls and 2-Acetyl-5-arylbenzofurans via Suzuki Coupling in Water under Thermal and Microwave Conditions. Synthesis. (2010): 3163\u0026ndash;3173\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShaaban MR, Darweesh AF, Dawood KM, Farag AM (2010) Mizoroki-Heck cross-couplings of 2-acetyl-5-bromobenzofuran and aryl halides under microwave irradiation. Arkivoc x, : 208\u0026ndash;225\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e[Job\u0026rsquo;s] P, Job (1928) Formation and stability of inorganic complexes in solution. Ann Chim 9:113\u0026ndash;203\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHolzwarth U, Gibson N (2011) The Scherrer equation versus the'Debye-Scherrer equation'. Nat Nanotechnol 6:534\u0026ndash;534\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKumar A, Rao GK, Kumar S, Singh AK (2014) Formation and role of palladium chalcogenide and other species in Suzuki\u0026ndash;Miyaura and Heck C-C coupling reactions catalyzed with palladium(II) complexes of organo-chalcogen ligands: realities and speculations. Organometallics 33(12):2921\u0026ndash;2943\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKumar A, Rao GK, Singh AK (2012) Organo-chalcogen ligands and their palladium(II)complexes: synthesis to catalytic activity for Heck coupling. RSC Adv 2:12552\u0026ndash;12574\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePhan NTS, Sluys MVD, Jones CW (2006) On the nature of the active species in palladium catalyzed Mizoroki\u0026ndash;Heck and Suzuki\u0026ndash;Miyaura couplings\u0026ndash;homogeneous or heterogeneous catalysis, a critical review. Adv Synth Catal 348:609\u0026ndash;679\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eSchemes 1 to 3 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Formamidinyl thiazoles, palladium, precatalysts, C-C cross-coupling, Suzuki-Miyaura, Water","lastPublishedDoi":"10.21203/rs.3.rs-7546711/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7546711/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe present work describes a facil access to novel nano-sized thiazole-based palladium(II) complexes from easily accessible starting precursors and elucidation of their structures by spectroscopic tools as well as physical characteristics. The efficiency of the synthesized complexes and their use as precatalysts for Suzuki Miyaura cross coupling reaction was investigated. Thiazole-based palladium(II) precatalysts could catalyze the C-C cross coupling reaction efficiently using water as a solvent under green mild reaction conditions.\u003c/p\u003e","manuscriptTitle":"Formamidinyl Thiazole-Based Palladium Complexes as Efficient Nano-sized Catalysts for Aqueous Suzuki –Miyaura Cross-Couplings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-18 11:31:53","doi":"10.21203/rs.3.rs-7546711/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f90f013a-86cd-4556-a1fa-6763ff1f0cac","owner":[],"postedDate":"September 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-08T08:09:06+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-18 11:31:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7546711","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7546711","identity":"rs-7546711","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}