Structure Of Co-2(Co)(6)(Dppm) And Co-2(Co)(5)(Chco2et)(Dppm) (Dppm = Ph2pch2pph2) And Exchange Reaction With (Co)-C-13: An Experimental And Computational Study

Crystal structures of Co-2(CO)(6)(dppm) (1) and Co-2(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 P-31 NMR spectra of 1 and 2 and in the solid-state and solution C-13 NMR spectra of 2 as well, but not in the solid-state and solution C-13 NMR spectra of 1. In CH2Cl2 solution under an atmosphere of (CO)-C-13, the CO ligands of both complexes exchange with (CO)-C-13. The overall rate of (CO)-C-13 exchange at 10 degrees C was found to be k(obs) = 0.107 x 10(-3) s(-1) for 1 and k(obs) = 0.243 x 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. (c) 2007 Elsevier B.V. All rights reserved.