Investigations on the Influence of Two Pyridyl-Mesoionic Carbene Constitutional Isomers on the Electrochemical and Spectroelectrochemical Properties of Group 6 Metal Carbonyl Complexes

Metal complexes of mesoionic carbenes (MICs) of the triazolylidene-type and their derivatives have gained increasing attention in the fields of electrocatalysis and photochemistry. The redox-activity of these metal complexes is critical for their applications in both the aforementioned fields. Easy accessibility and modular synthesis open a wide field for the design of ligands, such as bidentate ligands. The combination of a MIC with a pyridyl unit in a bidentate ligand setup increases the π-acceptor properties of the ligands while retaining their strong σ-donor properties. The analogy with the well-established 2,2'-bipyridine ligand allows conclusions to be drawn about the influence of the mesoionic carbene (MIC) moiety in tetracarbonyl group 6 complexes in cyclic voltammetry and (spectro-)electrochemistry (SEC). However, the effects of the different connectivity in pyridyl-MIC ligands remains underexplored. Based on our previous studies, we present here a thorough investigation of the influence of the two different pyridyl-MIC constitutional isomers on the electrochemical and the UV-vis-NIR/IR/EPR spectroelectrochemical properties of group 6 carbonyl complexes. Moreover, the presented complexes were investigated for the electrochemical conversion of CO2 using two different working electrodes, providing a fundamental understanding of the influence of the electrode material in the precatalytic activation.