Synthesis and reactivity of aryl- and alkyl-palladium(II) complexes with functional phosphines and phosphinoenolate ligands: First analogues of model nickel catalysts

Phenyl- and methyl-palladium(II) complexes analogous to model nickel(II) catalysts were prepared from readily available precursors. The methods used allow different ligands to be introduced in the co-ordination sphere. For example, the chelating phosphinoenolate ligand in [PdPh{Ph(2)PCH-C(-O)NPH2}L(2)] [L(2) = Ph(2)PCH(2)C(O)NPh(2)] was displaced by 1 equivalent of Ph(2)PCH(2)C(O)Ph (L(1)) to give [PdPh{Ph(2)PCH-C(-O)Ph}L(2)] whereas the terminal functional phosphine was displaced by P(C6H11)(3) to give [PdPh{Ph(2)PCH-C(-O)NPh(2)}{P(C6H11)(3)}]. Owing to favourable ligand-redistribution reactions, treatment of a mixture of complexes trans-[PdMe(Cl)L(2)(2)], trans-[PdMe(Cl)L(2)(1)] and trans-[PdMe(Cl)L(1)(L(2))] (which cannot be isolated pure) with an excess of NaOMe in toluene selectively afforded the phosphinoenolate complex [PdMe{Ph(2)PCH-C(-O)Ph}L(2)]. The enolate moiety of [PdPh{Ph(2)PCH-C(-O)NPh(2)}L(2)] and of [PdMe{Ph(2)PCH-C(-O)NPh(2)}L(2)] reacted with R'N=C=O(R' = Ph or p-tolyl) with formation of a carbon-carbon bond in a Michael-type addition and:the products were shown to exist in the form of two isomers a and b, characterised by a N-H ... O or a N-H ... N hydrogen bond within the ligand system. Insertion of CO into the Pd-Me bond of [PdMe{Ph(2)PCH-C(-O)NPh(2)}L(2)] or the corresponding acyl complexes. Although [PdMe{Ph(2)PCH-C(-O)Ph}(PPh(3))] inserted ethylene into its Pd-Me bond, as evidenced by quantitative formation of propylene, the palladium hydride thar must be generated by the beta-elimination reaction decomposes before further ethylene insertion can occur.