Transition metal complexes with sulfur ligands: Part CXLIV. Square planar nickel complexes with NiS4 cores in three different oxidation states: synthesis, X-ray structural and spectroscopic studies

The reaction of ‘buS2’2−=3,5-ditertiarybutyl-1,2-benzenedithiolate(2−) with Ni(ac)2·4H2O and subsequently AsPh4Cl, yielded (AsPh4)2[Ni(‘buS2’)2] (1). Complex 1 is extremely air sensitive and oxidized rapidly to give (AsPh4)[Ni(‘buS2’)2] (2). The anion of 2 could be further oxidized by iodine to give neutral [Ni(‘buS2’)2] (3). Complexes 1, 2 and 3 contain nickel in the formal oxidation states +2, +3 and +4, and could be completely characterized by X-ray structure determination and spectroscopic methods. The results indicate that the oxidation of 1→2→3 concerns electrons residing in molecular orbitals having [NiS4] character. No evidence could be obtained for an involvement of the benzene rings or an electron delocalization beyond the [NiS4] core. This conclusion corresponds with the reactivity of 3 versus 2 and 1 towards protons and CO. While 3 is inert to the attack of H+ and CO, 2 and 1 exhibit rapid reactions to give ‘buS2’H2 and either nickel–chloro complexes or Ni(CO)4.