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)(PBu 3 )Cl] (sacsac = pentane‐2,4‐dithionate = dithioacetylacetonate) with carbon monoxide (CO) has been examined by a combination of 31 P 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 δ 31 P 9.9 ppm. Carbon monoxide does not react with [Ni(sacsac)(PBu 3 )Cl], but [Ni(sacsac)(PBu 3 )(Cl)] reacts with any of Et 2 AlCl, BuLi, Li[Et 3 BH] or K[(s‐Bu) 3 BH] under an atmosphere of carbon monoxide in the presence or absence of olefin to produce [Ni(PBu 3 )(CO) 3 ], which has been identified by FTIR and 31 P NMR. [Ni(sacsac)(PBu 3 )Cl] reacts completely with BuLi or K[(s‐Bu) 3 BH] to form catalytically inactive species which yield active catalysts on addition of Et 2 AlCl.