Room Temperature Alkali Metal Reduction of Carbon Dioxide

The reduction of the relatively inert carbon–oxygen bonds of CO 2 to access useful CO 2 -derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO 2 and the MGE. Herein we report the first successful chemical reduction of CO 2 at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO 2 adduct ( 1 ) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO 2 )] n (M = Li, Na, K, 2 - 4 ) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M 2 (CAAC–CO 2 )] n ( 5 - 8 ). It is notable that these crystalline clusters of reduced CO 2 may also be isolated via the “one-pot” reaction of free CO 2 with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products 2 - 8 were investigated using a combination of experimental and theoretical methods.