Evaluation of mid-to-late transition metal imine catalysts for acetylene oligomerisation: A high activity bis(imino)pyridine iron(II) catalyst

Bis(imino)pyridine complexes of Co and Fe, and diimine complexes of Ni and Pd, have been tested as catalysts for acetylene oligomerisation and polymerisation. While Co, Ni and Pd complexes displayed low activity, an Fe complex led to an extremely active system for acetylene polymerisation after activation with methylaluminoxane (MAO). The product output could be shifted towards short-chain oligomers by addition of the chain transfer reagent ZnEt2, leading to polyene oligomeric chains bound to Zn. Complex branched and cyclic higher oligomers were partially identified, and some possible mechanisms for their formation proposed. The Fe system did not successfully catalyse copolymerisation of acetylene and ethylene, although there was evidence of limited acetylene incorporation into ethylene oligomers.