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) 3 COOH] ( 1 ) alone or together with fac -[Re(dmbpy)(CO) 3 CHO] ( 4 ) or other compounds which could be generated in photocatalytic reductions of CO 2 from fac -[Re(dmbpy)(CO) 3 Cl] 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 (OCO 2 )} ( 5 ), fac -[Re(dmbpy)(CO) 3 OH]·2.5H 2 O ( 8a ), { fac,fac -[Re(dmbpy)(CO) 3 ] 2 (H)}[OTf] ( 11 ), fac,fac -[Re(dmbpy)(CO) 3 CO 2 Re(bpy)(CO) 3 ] ( 13 ), fac -[Re(bpy)(CO) 3 OH] ( 17 ) and { fac,fac,fac- [Re(dmbpy)(CO) 3 ] 3 (OCO 2 )}[ReO 4 ] ( 18 ). Compounds 8a and 18 have been characterized by X-ray crystallography.