(eta 5-Cyclopentadienyl)(kappa 3-hydrotris(pyrazolyl)borate)cobalt(II)--the first high-spin cobalt organometallic complex

Cobalt Half-Sandwich, Sandwich, and Mixed Sandwich Complexes with Soft Tripodal Ligands

Reaction of sodium hydrotris(methimazolyl)borate (NaTm(Me)) with cobalt halides leads to the formation of paramagnetic pseudotetrahedral [Co(Tm(Me))X] (X = Cl, Br, I), of which the bromide has been crystallographically characterized. Mass spectrometry reveals the presence of higher molecular weight fragments [Co(Tm(Me))(2)](+) and [Co(2)(Tm(Me))(2)X](+) in solution. Aerial oxidation in donor solvents (e.g. MeCN) leads to formation of the [Co(Tm(Me))(2)](+) cation, which has been crystallographically characterized as the BF(4)(-), ClO(4)(-), Br(-), and I(-), salts. Attempts to prepare the mixed sandwich complex, [Co(Cp)(Tm(Me))](+), resulted in ligand decomposition to yield [Co(mtH)(3)I]I (mtH = 1-methylimidazole-2-thione), but with the more electron donating methylcyclopentadienyl (Cp(Me)) ligand, [Co(Cp(Me))(Tm(Me))]I was isolated and characterized. Electrochemical measurements reveal that the cobalt(III) Tm(Me) complexes are consistently more difficult to reduce than their Tp and Cp congeners.