Mechanism of CO 2 Fixation by Ir I –X Bonds (X = OH, OR, N, C)

Density functional theory calculations have been used to investigate the CO 2 fixation mechanism proposed by Nolan et al. for the Ir I complex [Ir(cod)(I i Pr)(OH)] ( 1 ; cod = 1,5‐cyclooctadiene; I i Pr = 1,3‐diisopropylimidazol‐2‐ylidene) and its derivatives. For 1 , our results suggest that CO 2 insertion is the rate‐limiting step rather than the dimerization step. Additionally, in agreement with the experimental results, our results show that CO 2 insertion into the Ir–OR 1 (R 1 = 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.