Cationic allylnickel complexes stabilized by a single N-heterocyclic carbene ligand (NHC) and a labile aquo or acetonitrile ligand have been synthesized by protonation of aryloxide-containing precursors. These complexes catalyze the polymerization of 1,3-butadiene and styrene, mimicking the analogous phosphine-based system.

Phosphinito-imines, a new class of P,N donors, are readily generated by reaction of bulky arylamide anions [R 2 CONAr]-(R 2 = Me or t-Bu; Ar = 2,6-i-Pr 2 C 6 H 4) with chlorophosphines ClP(R 1) 2. In solution, free phosphinito-imines exist in equilibrium with the corresponding amidophosphine tautomers, containing a nitrogen-bound P(R 1) 2 group. However, reacting the tautomer mixtures with metal precursor complexes, such as NiBr 2 (dme) or PdCl 2 (cod), selectively affords stable phosphinito-imine complexes MX 2 (P-N) (M = Ni, Pd) in excellent yields. These complexes are diamagnetic and exhibit square planar structures in the solid state, but in solution the Ni derivatives exchange with a small amount of the corresponding high-spin tetrahedral isomers. On treatment with MMAO or DEAC, NiX 2 (P-N) complexes become active ethylene oligomerization catalysts, affording mainly butenes along with smaller amounts of hexenes and octenes. The activity and the selectivity of these catalysts depend on the structure of the phosphinito-imine ligand and the co-catalyst used. When activated with DEAC, complexes containing the P(i-Pr) 2 moiety are extremely active, achieving TOFs over 10 6 mol C 2 H 4 /mol Ni •h and high selectivity for butenes.