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.