Cobalt half-sandwich, sandwich, and mixed sandwich complexes with soft tripodal ligands

Reaction of sodium hydrotris(methimazolyl)borate (NaTmMe) 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 BF4-, ClO4-, 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.