The synthesis, structure and electrochemical properties of new cobalt and nickel complexes based on ferrocenyl-containing o-iminophenols

[Display omitted] •New cobalt(II) and nickel(II) o-iminophenolato complexes with ferrocene backbone.•The X-ray structure of nickel(II) bis-o-iminophenolate; trans-position of ferrocene groups.•Complexes undergo series of electrochemical oxidations and reductions.•The oxidative addition of o-quinone to Co(II) o-iminophenolate to give Co(III) species. New cobalt(II) and nickel(II) bis-o-iminophenolato complexes of the type (Fc-CHN-ArO)2MII, where M = Co, ArO = C6H4O (1); M = Co, Ar = 4,6-tBu-C6H2O (2); M = Ni, Ar = 4,6-tBu-C6H2O (3), have been synthesized by the reaction of ferrocenyl-containing Schiff bases Fc-C(H)N-(C6H4)OH and Fc-C(H)N-(4,6-tBu-C6H2)OH with cobalt(II) chloride and nickel(II) acetate in methanol solution in the presence of base. Complexes 1–3 have been characterized in details by IR-spectroscopy, mass-spectrometry, cyclic voltammetry and NMR-spectroscopy (for 3). The molecular structure of nickel complex 3 in crystalline state was determined by single-crystal X-ray analysis. Nickel(II) complex 3 is diamagnetic and has a well-resolved NMR spectrum. Cobalt complexes 1 and 2 are paramagnetic. Their interaction with 3,6-di-tert-butyl-o-benzoquinone leads to new cobalt(III) o-benzosemiquinone complexes of the type (Fc-CHN-ArO)2MIII(3,6-DBSQ) 1a and 2a, respectively (3,6-DBSQ is 3,6-di-tert-butyl-o-benzosemiquinone) possessing a doublet spin state with resolved EPR spectra.