Influence of ligands and anions on the rate of carbon monoxide insertion into palladium-methyl bonds in the complexes (P-P)Pd(CH3)Cl and [(P-P)Pd(CH3)(L)]+SO3CF3- (P-P = dppe, dppp, dppb, dppf; L = CH3CN, PPh3)

Article abstract of DOI:10.1021/om00040a034

The preparation of the neutral complexes (P-P)Pd(CH₃)Cl (P-P = 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb), 1,1′-bis-(diphenylphosphino)ferrocene (dppf)) and the ionic complexes [(P-P)Pd(CH₃)(CH₃CN)]⁺SO₃CF ₃^- (P-P = dppe, dppp, dppb, dppf) is described. The ionic dppb complex was formed as a mixture of monomeric and oligomeric forms, which can be attributed to the length and the flexibility of the backbone of the ligand. The rate of CO insertion into the Pd-CH₃ bond in these complexes has been studied. The rate was found to decrease in the order dppb ≈ = dppp > dppf for the neutral complexes with half-life times ranging from 18 to 36 min at 235 K and 25 bar of CO. The dppe complex reacted much slower with a half-life time of 170 min at 305 K. The rate of carbonylation of the Pd-CH₃ bond in the cationic complexes was at least 10 times higher than those of the analogous neutral complexes, the order being dppb ≈ dppp ≈ dppf > dppe with half-life times <1.5 min at 235 K, except for the dppe complex, for which a half-life time of 2.5 min was measured. Carbonylation of the ionic PPh₃-coordinated complex [(dppp)Pd(CH₃)(PPh₃)]⁺-SO₃CF ₃^- was at least 2.5 times slower than that of the analogous CH₃CN-coordinated cationic complex.