| Abstract
| - Carbonylation reactions of (Ni-1)Pd(CH3)(Cl) and [(Ni-1)Pd(CH3)(OEt2)][BAr‘4] complexes, where Ni-1 is a strongly electron-donating metallodithiolate ligand, were investigated by IR and high-pressure NMR spectroscopy. Rates of CO insertion to form the derivatives (Ni-1)Pd(C(O)CH3)(Cl) and [(Ni-1)Pd(C(O)CH3)(CO)]+ are immeasurably fast at −80 °C in CD2Cl2, in contrast to slower rates for analogous diphosphine and diimine Pd complexes. Despite sluggish ethylene uptake, bulk copolymerization of CO/ethylene produces alternating polyketones.
- Neutral ((Ni-1)Pd(CH3)(Cl)) and cationic ([(Ni-1)Pd(CH3)(OEt2)][BAr‘4]) complexes containing thestrongly electron-donating metallodithiolate ligand Ni-1 ([(N,N‘-bis(2-mercaptoethyl)-N,N‘-diazacyclooctane]nickel(II), have been prepared. Carbonylation reactions withthese Pd−alkyl complexes were investigated by IR and high-pressure NMR spectroscopy. Carbon-13NMR spectroscopic studies showed that the rates of CO insertion to form the derivatives (Ni-1)Pd(C(O)CH3)(Cl) and [(Ni-1)Pd(C(O)CH3)(CO)]+ were immeasurably fast at −80 °C in CD2Cl2, in contrast toslower rates for Pd metal based diphosphine and diimine analogues. It was further shown that displacementof the terminally bound CO by ethylene in the acetylated derivative [(Ni-1)Pd(C(O)CH3)(CO)]+ wasslow, attributable to the high binding affinity of CO toward Pd2+ in the presence of the electron-richnickel dithiolate ligand. Bulk copolymerization studies of CO/ethylene in the presence of the cationiccatalyst precursor [(Ni-1)Pd(CH3)(OEt2)][BAr‘4] find alternating polyketones. The catalytic efficiency issolvent-dependent: CH2Cl2> CH3CN > THF. From low-pressure and bulk copolymerization studiesthe resting state of the catalyst was determined to be the open-chain intermediate [(Ni-1)Pd(C(O)R)(CO)]+ rather than the β- and γ-keto chelate complexes and that were found for diimines and diphosphines.
|
