Analysis of the structures of heterobimetallic active sites of metalloenzymes, evolutionarily perfected to perform reductions of simple substrates such as H+ and CO2, suggest that the base metals available to Nature are configured so as to function in 1) an electron-buffering capacity; b) push-pull mechanisms to couple or decouple substrates; or c) as the center of an innocent spectator ligand to maintain the coordination preferences of the active metal. The nickel/iron arrangement in the carbon monoxide dehydrogenase (CODH) enzyme is in the second category, with nickel binding the carbon of CO2 and a nearby iron interacting with an oxygen thus facilitating C-O bond cleavage. We have noted that MN2S2 metallodithiolates, M = Ni2+, Fe(NO)2+, and Co(NO)2+, as S-bound, bidentate metalloligands, have similar electron donor and buffering abilities as do the bipyridyls that facilitate CO2 reduction electrocatalysis in (bipy)Mn(CO)3Br and -Re(CO)3Cl.1 Like the bipy class ligands, the MN2S2 are also redox active, however they have a second feature, the Lewis acid M center that might aid in breaking the O-C bond of CO2 bound as CO22- to the Mn or Re. Hence we have prepared and characterized the title series of complexes, noting the butterfly M(µ-SR)2M’ core places the two metals ca. 3 Å apart.2 Computational studies have indicated a mechanism with intermediates similar to those in the CODH. Our work in this area will be described, including synthetic efforts to isolate intermediates.

Bifunctional metalloligands in MN2S2●Re/Mn(CO)3X complexes designed for CO2 reduction catalysts

255th National Meeting (2018)

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