SYNTHESIS AND CARBONYLATION STUDIES ON METHYLPALLADIUM(II) COMPLEXES CONTAINING CHELATING PYRIDINECARBOXYLATE LIGANDS - DYNAMIC BEHAVIOR OF THE LIGANDS AND IMPLICATIONS FOR THE CARBONYLATION MECHANISM

Methylpalladium complexes of the general formula [PdMe(pyca)(L)] [pyca = pyridine-2-carboxylate, L = PPh(3), PMePh(2), PMe(2)Ph, P(C(6)H(4)Me-p)(3), P(CH(2)Ph)(3). P(C6H11)(3), PPr3i, P(OMe)(3), pyridine, 4-methylpyridine or NMe(2)Ph] were synthesised and the dynamic behaviour of the ligands pyca and L studied in detail. The ligands were found to undergo readily a variety of exchange reactions, clearly demonstrating their lability under mild conditions. The ligand exchange behaviour and data on rates of carbonylation for the palladium complexes led to a dissociative mechanism, requiring lability in both the ligand L and the chelate, being proposed for the CO insertion process. The methylpalladium complexes exist in solution as a mixture of cis and trans isomers. However the acyl complexes were found to occur only in the geometry with the phosphine cis to the acyl group. X-Ray crystal structures were obtained for the complexes [Pd(COMe)(pyca){P(CH(2)Ph)(3)}] and [Pt(COMe)(pyca)-(PPh(3))]. The complexes have distorted square-planar geometry: for the palladium complex, which is highly distorted. P-Pd-O(21) 97.3(1), P-Pd-C(01) 88.9(2), N-Pd-O(21) 78.4(2) and N-Pd-C(01) 95.9(2)degrees and for the platinum complex P-Pt-O(21) 93.9(5), P-Pt-C(01) 95.1(9), N-Pt-O(21) 80.4(7) and N-Pt-C(01) 91(1)degrees.