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)2Co(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)2Co(NH2S(CH2)2NH2)]2(S2O6)3 and [Co((NH2S)2EDP)]Br have been
determined by X-ray crystallography, and the pKa of [(en)2Co(NH2S(CH2)2NH2)]3+ has been determined by
spectrophotometry. The pH dependencies of the kinetics of the linkage isomerization reactions have been studied
and yield pKa values of the S-bonded isomers. The (en)2Co 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.