Synthesis, structure, and dissociation equilibrium of [Co(η⁵-C₅H₅) (Se₂C₆H₄)]₂, a novel metalladiselenolene complex

A (phenylenediselenolato)cobalt complex dimer, [Co(η⁵-C₅H₅) (Se₂C₆H₄)]₂ (1), was synthesized by a reaction of carbonyl(η⁵-cyclopentadienyl)diiodocobalt(III) ([Co(η⁵-C₅H₅)I₂(CO)]) with poly(o-diselenobenzene). The structure of 1, determined by single-crystal X-ray crystallography, was found to be located in the space group of P2₁/c (No. 14), with a = 9.3346(5) Å, b = 11.6477(9) Å, c = 10.2179(5) Å, β = 111.491(1)°, and Z = 2. Covalent Co-Se bonds bridge the metal centers. In solution, dimers and monomers coexist at equilibrium. The dissociation equilibrium constant of 1 in solution was evaluated by ¹H NMR spectra at several temperatures between 20 and 80 °C. Dissociation enthalpies/entropies were found to be 50/110, 60/120, and 88 kJ mol^-1/200 J K^-1 mol^-1 in dimethyl sulfoxide-d₆, benzene-d₆, and chloroform-d₁, respectively.