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)

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)]+SO3CF3-(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 almost-equal-to 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 almost-equal-to dppp almost-equal-to 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)]+-SO3CF3- was at least 2.5 times slower than that of the analogous CH3CN-coordinated cationic complex.