CARBONYLATION OF HYDROCARBYLPALLADIUM(II) COMPLEXES CONTAINING SUBSTITUTED PYRIDINECARBOXYLATE CHELATING LIGANDS - STERIC AND ELECTRONIC MANIPULATION OF THE COINSERTION MECHANISM

Organopalladium(II) complexes of general formula [PdR(N-O)L] [R = Ph, N-O = pyridinecarboxylate (pyca), L = P(C6H11)(3); R = Ph, N-O = 6-met hylpyridinecarboxylate (mpyca), L = PPh(3), PMePh(2), P(C6H11)(3) or P Et(3); R = Ph, N-O = 4-nitropyridinecarboxylate (npyca), L = P(C6H11)( 3); R = Ph, N-O = 6-methyl-4-nitropyridinecarboxylate, L = P(C6H11)(3) ; R = Me, N-O = mpyca, L = PPh(3), P(CH(2)Ph)(3) or P(C6H11)(3); R = M e, N-O = npyca, L = PPh(3), PMePh(2) or P(C6H11)(3)] have been prepare d, and their carbonylation reactions studied in detail. Kinetic studie s of the CO-insertion process have indicated that the rate of reaction decreases as the basicity of the phosphine, L, increases. Complexes c ontaining the highly basic phosphine P(C6H11)(3) only undergo carbonyl ation if hemilability of the chelating ligand is promoted (by substitu tion of the N-O chelate). Substitution of the N-O ligand modifies the carbonylation pathway and provides an alternative route from that gene rally observed for palladium(II) and platinum(II) hydrocarbyl complexe s of pyca. A mechanism for insertion of CO involving partial dissociat ion of the N-O chelate is proposed for these complexes. The crystal st ucture of [PdMe(mpyca)(PPh(3))] has been determined. The complex has s quare-planar co-ordination with the nitrogen of pyca trans to the phos phorus. Considerable distortion of the inner co-ordination sphere is e vident, caused by steric interactions betwen the sigma-methyl ligand a nd the methyl group on the N-O ligand.