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

Abstract

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 incorporation of CO2 into such complexes. The systems investigated are various metal based congeners of the Ir-complex 8 [(cod)(IiPr)Ir-CCPh], with a ligand scaffold based on cod and IiPr ligands (cod = 1,5-cyclooctadiene; IiPr = 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

Carbon-carbon bonds with CO2: Insights from computational studies

“…It is not possible to conclude that one metal provides lowest barriers, however, it appears that Cu(I) generally gives feasible barriers, whereas Ni(II) may not be good for C-C bond formation with CO 2 [28,30,39]. All of the presented Cu-complexes use NHC ligands but as Lv et al indicated, other ligands, like e.g.…”

“…Based on the limited data for rhodium, insertion of CO 2 into a Rh-C sp bond involves no Rh-CO 2 interaction (Fig. 8) [28], as also observed for Cu. Insertion into Rh-C sp2 bonds occurs in a h 2 -fashion, where both C and O atoms coordinate to the metal Fig.…”

“…For copper catalysts, CO 2 interacts strongly with the metal and forms three-membered cyclic TSs during bond formation to C sp3 and C sp2 atoms [19,36,41,50], but not for reaction with C sp , where no CO 2 -metal interaction is seen [22,25,28] (Figs. 4, 6, 8), resulting in an acyclic TS (Fig.…”

“…Energetic considerations: In the discussed examples, the CO 2 insertion is generally rate-limiting [28,30,32,34,36,41]. It is not possible to conclude that one metal provides lowest barriers, however, it appears that Cu(I) generally gives feasible barriers, whereas Ni(II) may not be good for C-C bond formation with CO 2 [28,30,39].…”

“…The C-C bond formation involves three-membered cyclic TSs, with binding of CO 2 to the metal through both C and O (Figs. 8, 10 and 20) [22,28,30]. If another metal additive interacts with O, only the C-atom may interact with nickel ( Fig.…”