CO and Ethylene Migratory Insertion Reactions and Copolymerization Involving Palladium Complexes of a NiN2S2 Metallodithiolate Ligand

• Published in: Organometallics Vol. 26; no. 4; pp. 783 - 792
• Main Authors: Rampersad, Marilyn V, Zuidema, Erik, Ernsting, Jan Meine, van Leeuwen, Piet W. N. M, Darensbourg, Marcetta Y
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12-02-2007
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om0605783

Neutral ((Ni-1)Pd(CH3)(Cl)) and cationic ([(Ni-1)Pd(CH3)(OEt2)][BAr‘4]) complexes containing the strongly electron-donating metallodithiolate ligand Ni-1 ([(N,N‘-bis(2-mercaptoethyl)-N,N‘-diazacyclooctane]nickel(II), have been prepared. Carbonylation reactions with these Pd−alkyl complexes were investigated by IR and high-pressure NMR spectroscopy. Carbon-13 NMR 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 to slower rates for Pd metal based diphosphine and diimine analogues. It was further shown that displacement of the terminally bound CO by ethylene in the acetylated derivative [(Ni-1)Pd(C(O)CH3)(CO)]+ was slow, attributable to the high binding affinity of CO toward Pd2+ in the presence of the electron-rich nickel dithiolate ligand. Bulk copolymerization studies of CO/ethylene in the presence of the cationic catalyst precursor [(Ni-1)Pd(CH3)(OEt2)][BAr‘4] find alternating polyketones. The catalytic efficiency is solvent-dependent:  CH2Cl2 > CH3CN > THF. From low-pressure and bulk copolymerization studies the 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.