Structure of Co2(CO)6(dppm) and Co2(CO)5(CHCO2Et)(dppm) (dppm = Ph2PCH2PPh2) and exchange reaction with 13CO: An experimental and computational study

Crystal structures of Co2(CO)6(dppm) (1) and Co2(CO)5(CHCO2Et)(dppm) (2) (dppm = Ph2PCH2PPh2) show asymmetry with respect to the orientation of the phenyl groups in 1 and owing to the bridging ethoxycarbonylcarbene ligand in 2. The effect of this asymmetry was recognized in the solid-state 31P NMR spectra of 1 and 2 and in the solid-state and solution 13C NMR spectra of 2 as well, but not in the solid-state and solution 13C NMR spectra of 1. In CH2Cl2 solution under an atmosphere of 13CO, the CO ligands of both complexes exchange with 13CO. The overall rate of 13CO exchange at 10 °C was found to be kobs = 0.107 × 10−3 s−1 for 1 and kobs = 0.243 × 10−3 s−1 for 2. Two-layered ONIOM(B3LYP/6-31G(d):LSDA/LANL2MB) studies revealed fluxional behavior of 1 with rather small barriers of activation of the rearrangements. Four possible isomers have been computed for 2, close to each other energetically.