Mechanism of CO2 Fixation by IrI-X Bonds (X = OH, OR, N, C)

Density functional theory calculations have been used to investigate the CO2 fixation mechanism proposed by Nolan et al. for the IrI complex [Ir(cod)(IiPr)(OH)] (1; cod = 1,5‐cyclooctadiene; IiPr = 1,3‐diisopropylimidazol‐2‐ylidene) and its derivatives. For 1, our results suggest that CO2 insertion is the rate‐limiting step rather than the dimerization step. Additionally, in agreement with the experimental results, our results show that CO2 insertion into the Ir–OR1 (R1 = H, methyl, and phenyl) and Ir–N bonds is kinetically facile, and the calculated activation energies span a range of only 12.0–23.0 kcal/mol. Substantially higher values (35.0–50.0 kcal/mol) are reported for analogous Ir–C bonds. We report the DFT‐based investigation of the mechanism of CO2 insertion into IrI–C and IrI–heteroatom bonds (such as Ir–N and Ir–O). The calculated barriers show that CO2 insertion is the rate‐limiting step, in accordance with experimental results.