Dinuclear nickel complexes with bidentate N,O ligands: synthesis, structure, and catalytic oligomerization of ethylene.

Abstract

The new dicationic dinuclear complexes [Ni(micro-Cl)(2)(N,OH)(2)]Cl(2) (11, N,OH = 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-propan-2-ol; 12, N,OH = 2-pyridin-2-yl-propan-2-ol) were prepared in good yields and evaluated as precatalyts in the oligomerization of ethylene, using MAO or AlEtCl(2) as cocatalyst. These paramagnetic complexes were characterized by single-crystal X-ray diffraction in the solid state and in solution with the help of the Evans method, which revealed agreement between the octahedral coordination spheres found in solution and in the solid state. The N donor atoms of each chelating ligand are in mutual cis position, and the OH donors are mutually trans situated. Selectivities for 1-butene within the C(4) fraction of 61% (11) and 58% (12) were observed in the presence of 200 equiv of MAO, but better turnover frequencies (28 300 (11) and 20 400 (12) mol of C(2)H(4)/(mol of Ni.h)) were obtained when 800 equiv of MAO was used. In the presence of 6 equiv of AlEtCl(2), the activities were considerably increased, up to 174 300 (11) and 97 100 (12) mol of C(2)H(4)/(mol of Ni.h), and the selectivity for C(4) olefins was 70% and 64%, respectively.