The activation of a metal alkyl-free Ni-based catalyst with B(C6F7)(3) was investigated in the polymerization of 1,3-butadiene. A catalyst of bis(1,5-cyclooctadiene)nickel (Ni(COD)(2))/B(C6F7), was found to have high catalytic activity and 1,4-cis stereoregularity. The catalyst was also found to provide polybutadiene having a molecular weight (M-W) of up to 117,000, even in the absence of AlR3 and MAO. Variations in the mol ratio of B(C6F5)(3) to Ni affected catalytic activity, 1,4-cis stereoregularity, and the M-W of polybutadiene, while the molecular weight distribution (MWD) of polybutadiene showed little correlation with the mol ratio of B(C6F5)(3) to Ni. The use of other borane compounds such as B(C6H5)(3), BEt3, and BF3 etherate in place of B(C6F5)(3) clearly showed the two main functions of B(C6F5)(3) in the present catalyst. The high Lewis acidity of B(C6F5)(3) enabled it to activate catalytic complexes, thus inducing the polymerization. The steric bulkiness of B(C6F5)(3) suppressed chain transfer reactions, contributing to the production of polybutadiene with a high M-W. Mnetic studies showed that the catalyst had an induction period, possibly due to the time needed for the formation of catalytic complexes starting from Ni(COD)(2). A plot of -In (1-X), where X is the fractional conversion, as a function of time resulted in a linear relationship, showing that the present catalyst system followed first-order kinetics with respect to monomer concentration. (C) 2004 Wiley Periodicals, Inc.