Bis(chelated) palladium(II) complexes with a diphosphine and a dinitrogen ligand: very efficient catalyst precursors in the co- and ter-polymerisation of CO and olefins

Abstract

A new series of palladium(II) complexes of general formula [Pd(dppp)(L–L)][PF₆]₂ has been synthesised and characterised [dppp = Ph₂P(CH₂)₃PPh₂, L–L = 2,2′-bipyridine (bipy), 4,4′-dimethyl-2,2′-bipyridine, phenanthroline or 3,4,7,8-tetramethyl-1,10-phenanthroline]. The crystal structure of [Pd(dppp)(bipy)][PF₆]₂ has been determined. The chemical behaviour of the complexes in solution has been studied by NMR spectroscopy. Depending on the nature of the solvent, the chemical environment of palladium in solution can be either the same as in the solid state or different. Whereas in CD₂Cl₂ the co-ordination sphere remains intact, partial dissociation of the nitrogen ligand occurs in co-ordinating solvents. The complexes were found to be very active catalyst precursors in the CO–olefin co- and ter-polymerisation reactions. Detailed investigation of their catalytic activity allowed the catalyst precursor to be considered as the result of the assembly of different parts, each with a well defined role. In particular, the dissociated N-donor modulates the proton concentration, thus affecting the length of the polymeric chain.