Carbon monoxide poisoning as a probe for the active site(s) of a nickel-based olefin oligomerization catalyst

The interaction of the olefin oligomerization catalyst system derived from [Ni(sacsac)(PBu3)Cl] (sacsac = pentane‐2,4‐dithionate = dithioacetylacetonate) with carbon monoxide (CO) has been examined by a combination of 31P NMR and FTIR spectroscopy. The catalyst is rapidly and completely inhibited by CO; however, removal of the CO restores catalytic activity. A CO‐adduct of the active catalyst has a characteristic CO stretching frequency of 2042 cm−1, and δ31P 9.9 ppm. Carbon monoxide does not react with [Ni(sacsac)(PBu3)Cl], but [Ni(sacsac)(PBu3)(Cl)] reacts with any of Et2AlCl, BuLi, Li[Et3BH] or K[(s‐Bu)3BH] under an atmosphere of carbon monoxide in the presence or absence of olefin to produce [Ni(PBu3)(CO)3], which has been identified by FTIR and 31P NMR. [Ni(sacsac)(PBu3)Cl] reacts completely with BuLi or K[(s‐Bu)3BH] to form catalytically inactive species which yield active catalysts on addition of Et2AlCl.