Nickel Complexes Featuring Iminophosphorane–Phenoxide Ligands for Catalytic Ethylene Dimerization

A series of bidentate ligands associating
an iminophosphorane and
a phenoxide were synthesized and coordinated to nickel­(II), leading
initially to bimetallic KNi adducts. Replacement of the potassium
by another metal allowed the isolation and characterization of bimetallic
LiNi and AlNi complexes, while addition of one equivalent of triphenylphosphine
gave access to monometallic complexes. The same type of complex was
obtained with the coordination of a tridentate ligand incorporating
a supplementary amine donor. These paramagnetic complexes were characterized
by elemental analysis, and some of them by X-ray diffraction, evidencing
a tetrahedral nickel center. They were shown to efficiently catalyze
the oligomerization of ethylene in the presence of Et2AlCl
(Al/Ni = 22.5) with TOF up to 72  000 mol­(C2H4)/mol­(Ni)/h, giving selectively butene (more than 97%) with
at best 93% of 1-C4.