SYNTHESIS AND REACTIVITY OF ARYL-PALLADIUM(II) AND ALKYL-PALLADIUM(II) COMPLEXES WITH FUNCTIONAL PHOSPHINES AND PHOSPHINOENOLATE LIGANDS - FIRST ANALOGS OF MODEL NICKEL-CATALYSTS

Phenyl- and methyl-palladium(II) complexes analogous to model nickel(I I) catalysts were prepared from readily available precursors. The meth ods used allow different ligands to be introduced in the co-ordination sphere. For example, the chelating phosphinoenolate ligand in [PdPh{P h(2)PCH-C(-O)NPH2}L(2)] [L(2) = Ph(2)PCH(2)C(O)NPh(2)] was displaced b y 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 [P dMe{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 Mi chael-type addition and:the products were shown to exist in the form o f two isomers a and b, characterised by a N-H ... O or a N-H ... N hyd rogen bond within the ligand system. Insertion of CO into the Pd-Me bo nd of [PdMe{Ph(2)PCH-C(-O)NPh(2)}L(2)] or the corresponding acyl compl exes. 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 r eaction decomposes before further ethylene insertion can occur.