Synthesis and Reactions of fac-[Re(dmbpy)(CO)₃X] (dmbpy = 4,4‘-Dimethyl-2,2‘-bipyridine; X = COOH, CHO) and Their Derivatives

Reactions of fac-[Re(dmbpy)(CO)₃COOH] (1) alone or together with fac-[Re(dmbpy)(CO)₃CHO] (4) or other compounds which could be generated in photocatalytic reductions of CO₂ from fac-[Re(dmbpy)(CO)₃Cl] have been studied to establish possible routes to CO and formate. The results suggest that the reactions of 1 are governed by complex equilibria involving its ionization to Re(dmbpy)(CO)₄⁺ and OH^- or proton transfer to highly basic species. Parallel reaction paths, emanating from Re(dmbpy)(CO)₄⁺, are suggested to account for the formation of CO and formate in the catalytic reactions and support the proposal that 4 is a likely catalytic intermediate in addition to 1. New compounds have been isolated or prepared in order to support proposals about reaction pathways:  {fac-[Re(dmbpy)(CO)₃]₂(OCO₂)} (5), fac-[Re(dmbpy)(CO)₃OH]·2.5H₂O (8a), {fac,fac-[Re(dmbpy)(CO)₃]₂(H)}[OTf] (11), fac,fac-[Re(dmbpy)(CO)₃CO₂Re(bpy)(CO)₃] (13), fac-[Re(bpy)(CO)₃OH] (17) and {fac,fac,fac-[Re(dmbpy)(CO)₃]₃(OCO₂)}[ReO₄] (18). Compounds 8a and 18 have been characterized by X-ray crystallography.