Synthesis of methyl-palladium(II) and -platinum(II) complexes containing labile chelates and olefinic tertiary phosphine ligands: Intramolecular insertion of an olefin into a palladium-carbon bond, and activation of a carbon-hydrogen bond by a platinum(II) complex

The square planar complexes [M(Me)(L-L)(L)] {M = Pd, L = dpvp [PPh(2)(C6H4CH=CH2-o)], L-L = acac (acetylacetonate), bzsac (1-phenyl-3-sulfanylbut-2-en-1-onate) or pyca (pyridine-2-carboxylate), L = PPh(2)(C(6)H(4)Et-o), L-L = acac or pyca, L = P(CH2-CH=CH2)Ph(2), L-L = pyca; M = Pt, L = dpvp, L-L = bzsac or pyca, L = PPh(2)(C(6)H(4)Et-o), L-L = pyca} have been synthesised and their thermal behaviour studied;. Heating the palladium-dpvp complexes in benzene leads to intramolecular migratory insertion of the vinyl double bond of the phosphine into the Pd-Me bond to give complexes with a five-membered palladacyclic ring, [Pd(L-L){PPh(2)(C(6)H(4)CHCH(2)Me)}]. In contrast. warming the platinum complex [PtMe(pyca)(dpvp)] leads to a cyclometallation reaction forming a platinacycle with a platinum-alkenyl bond [Pt(pyca){PPh(2)(C6H4C=CH2)}]. The platinum complex appears to react by oxidative addition of the vinyl C-H bond of dpvp to Pt-II; methane is eliminated during the reaction. Although no such species has been identified, kinetic evidence suggests that the two thermal processes occur via a common four-co-ordinate intermediate containing a 'dangling' pyca ligand and with dpvp chelated through the phosphorus and the vinyl double bond [M(Me)(pyca){PPh(2)(C6H4CH=CH2)}].