EPR spectroscopy of catalytic systems based on nickel complexes of 1,4-diaza-1,3-butadiene (alpha-diimine) ligands in hydrogenation and polymerization reactions

The catalytic systems based on .-diimine complexes of Ni(0) and Ni(II) of the general formulas NiBr₂(DAD-R) (R = -C_3H7 or -CH₃) and Ni(DAD-CH₃)₂ (DAD(-C₃H₇) = 1,4-bis(2,6-diiso-propylphenyl)-2,3-(dimethyl-1,4-diazabuta-1,3-diene, DAD(-CH₃) = 1,4-bis 2,6-dimethylphenyl)-2,3-dimethyl-1,4-diazabuta-1,3-diene), with Lewis acids (AlEt₃, AlEt₂Cl, AlEtCl₂, B(F₅C₆)₃, BF₃ centre dot OEt₂) in hydrogenation and polymerization reactions were investigated by the EPR spectroscopy method. The Ni(I) complexes of a (DAD-R)NiX₂AlXy(C₂H₅)_3-y composition (instead of the aluminum atom may be a boron atom) were identified where R = -CH₃ or -C₃H₇, X = Br, X = Cl or -C₂H₅. The .-diimines radical-anions are included in the derivatives of aluminum or boron. It is found that there occur oxidation reactions between Ni(DAD-CH₃)₂ and aluminum organic compounds or boron derivatives, resulting in the formation of paramagnetic complexes. It is shown that there is no direct relationship between activity in polymerization or hydrogenation reactions and concentration of paramagnetic particles.