Synthesis, Structure, and Dissociation Equilibrium of [Co(eta5-C5H5)(Se2C6H4)]2, a Novel Metalladiselenoicne Complex

A (phenylenediselenolato)cobalt complex dimer, [Co(eta5ʹ-C5H5)(Se2C6H4)]2 (1), was synthesized by a reaction of carbonyl(eta5-cyclopentadienyl)diiodocobalt(llI) ([Co(eta5-C5H5)12(CO0)]) 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) A, b = 11.6477(9) A, c = 10.2179(5) A, beta = 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 mol11/200 J K^-1 mol^-1 in dimethyl sulfoxide-d6, benzene-d6, and chloroform-d1, respectively.