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).