Cobalt and Nickel Complexes Bearing Pyrazolyliminophosphorane Ligands: Synthesis, Characterisation and Catalytic Ethylene Oligomerisation Behaviour

Abstract

Abstract Treatment of 1‐(2′‐azidophenyl)‐3,5‐dimethylpyrazole ( 1 ) with Ph 2 PR (R = Ph, Me) and (Ph 2 P) 2 CH 2 , respectively, affords the pyrazolyliminophosphoranes 2 , 3 and 4 . Reaction of 2 or 3 with [NiCl 2 (dme)] or NiBr 2 yields the N,N‐chelate nickel complexes 5 – 8 , and with CoCl 2 complexes 9 and 10 . Reaction of 4 with [NiCl 2 (dme)], NiBr 2 and CoCl 2 , respectively, affords the N,N,P‐chelate complexes 11 – 13 . Compounds 2 – 4 were characterised by 1 H, 13 C, 31 P NMR and IR spectroscopy and elemental analysis, while complexes 5 – 13 were characterised by IR spectroscopy and elemental analysis. The structures of complexes 5 , 9 and 12 were further characterised by single‐crystal X‐ray diffraction techniques. Complexes 5 – 13 are active catalysts for ethylene oligomerisation upon activation with alkylaluminium derivatives(Et 2 AlCl, MAO or MMAO). These complexes exhibit good to high catalytic activities (up to 3.54 × 10 6 g mol –1 h atm for the nickel complexes and 5.48 × 10 5 g mol –1 h atm for the cobalt complexes). The effects of varying ethylene pressure, temperature and aluminium co‐catalyst/Ni or Co ratios with complexes 5 , 9 , 11 and 12 are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)