SINGLE-ELECTRON OXIDATION OF NICKEL(0) COMPLEXES WITH C-H ACIDS BASED ON THE DATA OF EPR-SPECTROSCOPY

The results of the ESR spectroscopic studies of catalytic systems based on Ni(0) complexes and a number of C-H acids are presented. It is shown that the interaction of Ni(COD)(2) and Ni(PPh3)(4) with beta-diketones and 1,3-cyclopentadiene (Cp-H) produces Ni(I) paramagnetic complexes that are sufficiently stable at room temperature with characteristic Ni-C sigma-bonds. Schemes of interaction of Ni(COD)(2) and Ni(PPh3)(4) with beta-diketones (C-H acid) and stabilization of Ni(I) in these systems are proposed. It is shown that reactions of Ni(COD)(2) and Ni(PPh3)(4) with beta-diketones (C-H acid) occur stepwise: in the first stage, Ni(0) is oxidized to Ni(II), in the second stage, a disproportionation reaction takes place Ni(II) + Ni(0) = 2Ni(I), as a result of which the paramagnetic nickel(I) complex is formed. The paramagnetic Ni(I) complexes with coordinated ethylene are identified. It is shown that during the evacuation of the system, ethylene is eliminated with the formation of the initial complex Ni(I) and the subsequent effecting of ethylene again leads to the formation of a complex of nickel(I) with coordinated ethylene. After ethylene interaction with nickel(I) complexes bearing in their composition two molecules of the triphenylphosphine ligand, one of the triphenylphosphine ligands is replaced by an ethylene molecule. It has been established that nickel(I) complexes with two triphenylphosphine ligands have a square-planar structure and, when one of the phosphine ligands is replaced by an ethylene molecule, the resulting Ni(I) complex is characterized by a tetrahedrally distorted local structure of the Ni(I) ion. The values of the magnetic resonance parameters of the identified Ni(I) complexes are specified by comparing the calculated and experimental spectra using the "Easy spin" program module