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, LiEt₃BH] 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.