Ab initio MO/MP4, SD-CI, and CCD (coupled cluster (doubles)) calculations are carried out on the insertion reactions of CO2 and C2H4 into the Cu-R (R = H, CH3, and OH) bond. The insertion into the Cu-CH3 bond occurs with a higher activation energy than the corresponding insertion into the Cu-H bond. This is because Cu(CH3)(PH3)(2) distorts at the TS to a greater extent than CuH(PH3)(2), due to the highly directional sp(3) valence orbital of CH3 unlike the spherical Is valence orbital of H. The CO2 insertion into the Cu-H and Cu-CH3 bonds occurs with a lower activation energy and a higher exothermicity than the C2H4 insertion. The higher exothermicity of the CO2 insertion is because the Cu-OC(O)R bond is stronger than the Cu-CH(2)CH(2)R bond. The reason for the lower activation energy is that the pi orbital of CO2 lies at lower energy level than that of C2H4; accordingly, the exchange repulsion between R and CO2 is smaller than that between R and C2H4. The CO2 insertion into the Cu-OH bond proceeds with no barrier. The main reason is that the lone-pair orbital of OH, which is not used for coordination to Cu, can form a bonding interaction between OH and CO2 without weakening of the Cu-OH bond.