Nickel(II) catalysed co-polymerisation of CO and ethene: Formation of polyketone vs. polyethylene – The role of co-catalysts

The square planar Ni complex (SP-4-3)-[Ni(2-tol)(PPh3)(N,O)] (N,O = (Z)-4,4,5,5,6,6,6-heptafluoro-3-oxo-2-(pyrrolidine-2-ylidene)-hexanenitrile) is an active catalyst for the co-polymerisation of CO and ethene yielding aliphatic polyketone. Addition of Lewis acids like BPh3 or B(C6F5)3 as co-catalyst accelerates the polymerisation but not the lifetime of the catalyst and leads to a mixture of polyethylene and polyketone. Addition of the Lewis base triphenylphosphane (PPh3) completely suppresses the formation of polyethylene. The polymers formed were characterised by IR spectroscopy, 13C cross polarisation (CP) magic angle spinning (MAS) solid state NMR spectroscopy, differential scanning calorimetry (DSC) and size exclusion chromatography (SEC).