Ethylene polymerization catalysts based on nickel(II) 1,4-diazadiene complexes: the influence of the 1,4-diazadiene backbone substituents on structure and reactivity

Thermally sensitive dialkyl nickel complexes {DAD(H,H)}Ni(CH2SiMe3)(2) and {DAD(Me,Me)}Ni(CH2SiMe3)(2) [DAD(X,X)= 2,6-iPr(2)C(6)H(4)-N=C(X)-C(X)=N-C(6)H(4)iPr(2)-2,6] were synthesized and were characterized by X-ray diffraction studies on single crystals. The substituents X on the backbone of the alpha-diimine ligand significantly influence the conformation of the 2,6-diisopropylphenyl substituents. This effect is thought to be of crucial importance for the polymerization of ethylene when {DAD(X,X)}NiBr2/MAO is used as catalyst. The influence of the catalyst structure, pressure, and temperature on the polymerization activity, molar mass, glass transition temperature, melting temperature and branching of the polymers has been studied. The dialkyl complex {DAD(H,H)}Ni(CH2SiMe3)(2) underwent rapid reductive carbonylation giving the dicarbonyl complex {DAD(H,H)}Ni(CO)(2) along with both bis(trimethylsilyl)ethane and alpha,alpha'-bis(trimethylsilyl)acetone. The dicarbonyl {DAD(H,H)}Ni(CO)(2) was characterized by X-ray crystallography. (C) 1998 Elsevier Science S.A. All rights reserved.