How easy is CO2 fixation by M-C bond containing complexes (M = Cu, Ni, Co, Rh, Ir)?

A comparison between different M-C bonds (M = Cu(I), Ni(II), Co(I), Rh(I) and Ir(I)) has been reported by using density functional theory (DFT) calculations to explore the role of the metal in the fixation or in-corporation of CO2 into such complexes. The systems investigated are various metal based congeners of the Ir-complex 8 [(cod)((IPr)-Pr-i)Ir-CCPh], with a ligand scaffold based on cod and (IPr)-Pr-i ligands (cod = 1,5-cyclo-octadiene; (IPr)-Pr-i = 1,3-bis(isopropyl)imidazol-2-ylidene). The results of this study show that the calculated CO2 insertion barriers follow the trend: Cu(I) (20.8 kcal mol(-1)) < Rh(I) (30.0 kcal mol(-1)) < Co(I) (31.3 kcal mol(-1)) < Ir(I) (37.5 kcal mol(-1)) < Ni(II) (45.4 kcal mol(-1)), indicating that the Cu(I) based analogue is the best CO2 fixer, while Ni(II) is the worst in the studied series