Reaction of elemental sulphur with cobalt(II)-Schiff-base complexes: synthesis of µ-disulphido and µ-tetrasulphido binuclear cobalt(III) complexes. Crystal structures of two binuclear cobalt(III)-Schiff-base complexes

Abstract

Reaction of elemental sulphur with cobalt(II)–quadridentate Schiff-base complexes is reported. Elemental sulphur reacts with [Co(salphen)][salphen =NN′-o-phenylenebis(salicylideneiminate)],(1), [Co(salen)][salen =NN′-ethylenebis(salicylideneiminate)],(2), [Co{3,3′-(MeO)₂-salen}], (3), and [Co(α,α′-Et₂-salen)], (4), in co-ordinating solvents to afford binuclear, diamagnetic cobalt(III) complexes containing a tetrasulphido bridging ligand: [{Co(salphen)}₂(µ-S₄)L₂][L = tetrahydrofuran (thf)(5) or pyridine (py)(6)]; [{Co(salen)}₂(µ-S₄)(thf)], (7); [{Co(salen)}₂(µ-S₄)(py)₂], (8); [(Co)3,3′-(MeO)₂-salen]}₂(µ-S₄)], (9); [{Co(α,α′-Et₂-salen)}₂(µ-S₄)(thf)], (10). Substituents on the quadridentate ligand do not affect the nature of the final compound. Carrying out the reaction of (1) with elemental sulphur in thf containing NaBPh₄ results in the formation of a completely different compound, which was isolated and structurally characterized as [{Co(salphen)}₂S₂Na(thf)₂]BPh₄, (11). This is a diamagnetic binuclear cobalt(III) complex, in which the two Co(salphen) units are bridged by the S₂^2– ligand and by the Na⁺ which is bonded to all four oxygen atoms of the Schiff-base ligands [Co–S 2.231(7), 2.249(7); S–S 1.962(9)Å]. Both the genesis and the stability of (11) are dependent on Na⁺. The complex [Co(salphen)] binds Na⁺ in a thf solution to form a binuclear complex, [{Co(salphen)}₂Na(thf)₂]BPh₄, (12), the structure of which shows two Co(salphen) units arranged around Na⁺ creating a cavity between the two planar units for the S₂ ligand. Attempts to remove Na⁺ from (11) by using 18-crown-6 ether resulted in decomposition of the Co–S₂–Co fragment and the formation of (5) and (1). Complex (11) can transfer a single sulphur atom to [Fe(salen)] and PPh₃, or the S₂ unit to [V(η-C₅Me₅)₂], resulting in formation of (12). Lithium, potassium, and guanidinium cations affect the reaction of [Co(salphen)] with elemental sulphur much less than the Na⁺. Crystallographic details for complex (11) are space group P(triclinic), a= 11.816(1), b= 15.949(2), c= 17.437(2)Å, α=93.70(1), β= 93.90(1), γ= 94.86(1)°, Z= 2, R 0.059 (R′= 0.058) for 1 479 observed reflections; and for complex (12) are space group Pnna(orthorhombic), a= 20.223(4), b= 29.197(8), c= 20.204(4)Å, Z= 8, and R 0.065 (R′= 0.069) for 1 516 observed reflections.