EPR study of mono-o-iminobenzosemiquinonato nickel(II) complexes with Ni–C σ-bond

New square-planar (Ph3P)NiII(o-Tol)(ISQ-Pri) (1), (Ph3P)NiII(o-Tol)(ISQ-Me) (2), (Ph3P)NiII(o-Tol)(ISQ-But) (3) nickel complexes (where ISQ-Pri = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate, ISQ-Me = 4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate, ISQ-But = 4,6-di-tert-butyl-N-(2,5-di-tert-butylphenyl)-o-iminobenzosemiquinonate, o-Tol = o-tolyl ligand) have been synthesized. Complexes contain σ-bound o-tolyl and neutral donor ligand Ph3P. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands lead to the tetrahedral distortion of square-planar configurations of complexes as it was established using EPR spectroscopy.