Linkage isomerism, structure, and reactivity studies of sulfenamide complexes of cobalt(III)

The S-bonded sulfenamide isomers have been prepared by the known reaction of hydroxylamine-O-sulfonate with (en)(2)Co(III) thiolate complexes of aminoethanethiol, cysteine, and penicillamine and the cis dithiolate formed by N,N'-ethylene-di-penicillamine (EDP) and Co(III). It is shown that the sulfenamides undergo linkage isomerization in alkaline solution to produce their respective N-bonded linkage isomers. The addition of acid yields the protonated N-bonded isomers. The structures of [(en)(2)Co(NH(2)S(CH(2))(2)NH(2))](2)(S(2)O(6))(3) and [Co((NH(2)S)(2)EDP)]Br have been determined by X-ray crystallography, and the pK(a) of [(en)(2)Co(NH(2)S(CH(2))(2)NH(2))](3+) has been determined by spectrophotometry. The pH dependencies of the kinetics of the linkage isomerization reactions have been studied and yield pK(a) values of the S-bonded isomers. The (en)(2)Co systems give only the acid-stable N,N' isomer at equilibrium, whereas the EDP complex gives a mixture of N,N' and N,S isomers at pH 7-9.