A proton directly attacks 1,5-cyclooctadiene in bis(1,5-cyclooctadiene)nickel(O) in the formation of a Keim type oligomerization catalyst

Full proton and carbon assignments have been obtained for ((1,4,5-eta)-cycl ooctenyl)(1,1,1,5,5,5-hexafluoro-2,4-pentadionato)nickel(II) (1), a Keim ty pe ethylene oligomerization catalyst, which is afforded by treatment of bis (1,5-cyclooctadiene)nickel with 1,1,1,5,5,5-hexafluoroacetylacetone. The la rger metallacycle formed by nickel and the (1,4,5-eta)-cyclooctenyl ligand in 1 is shown to be in a "nickela chair" conformation. The reaction of bis( 1,5-cyclooctadiene)nickel with 1,1,1,5,5,5-hexafluoroacetylacetone-d(2) at low temperature shows a 70% incorporation of a deuterium atom anti to nicke l at a beta-carbon. This observation is incompatible with a hydride migrati on path for the formation of 1 but fully consistent with a direct protonati on of an alkene coordinated to an electron-donating nickel.