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.
van Ommen, J. G., van der Ploeg, H. J., van Berkel, P. C. J. M., & Mars, P. (1977). An infrared investigation of the catalyst formation in the system Ni(acac)2, C3H4, (iBu)3AL for propadiene polymerization. Journal of molecular catalysis, 2(6), 409-420. https://doi.org/10.1016/0304-5102(77)80012-6