The catalytic system Ni (COD) 2/BF3· OEt2 has been studied in conversions of 1, 5- cyclooctadiene under argon and ethylene atmosphere. It has been demonstrated that the catalytic system formed under argon exhibits a high effectiveness in cycloisomerization of 1, 5-COD surpassing in this characteristic all known nickel complex catalysts (selectivity to bicyclo-[3.3. 0]-octene-2 is up to 99.5% at 100% conversion). In the case of ethylene ...