An infrared investigation of the catalyst formation in the system Ni(acac)2, C3H4, (iBu)3AL for propadiene polymerization

Abstract

The catalyst formation in the system Ni(acac)2, C3H4, (iBu)3Al was investigated by means of infrared spectroscopy. It was found that the Al(acac)3 and (iBu)2Al(acac) formed are both by-products of catalyst formation without a catalytic activity. Ni(acac)2 loses its acac groups forming the unstable (iBu)2Ni compound; without C3H4 being present, this compound disproportionates to Ni metal and isobutane and isobutene. In the presence of C3H4 an allyl-nickel complex is formed, which reacts with (iBu)3Al to give the actual catalyst, possibly a bimetallic allyl—nickel-aluminium complex. Catalysts such as Ni(acac)2, C3H4, (iBu)3Al and (πC3H5)2Ni with or without (iBu)3Al all selectively give 1, 2, 1, 2-polypropadiene. A Lewis base like pyridine not only decreases the polymerization rate but also changes the selectivity towards the formation of 1, 2, 2, 1-polymer