Reaction of thiols with N-bonded sulfenamide complexes of cobalt(III): steric effect and reaction pathway.
The products and kinetics of the reaction of several thiols (RSH = 2-aminoethanethiol, cysteine, penicillamine, cysteine ethyl ester) with N-bonded sulfenamide complexes ([Co(en)(2)(NH(2)S(CH(2))(2)NH(2)](3+) (IA), [Co(en)(2)(NH(2)SCH(2)CH(CO(2)H)NH(2)](3+) (IC), [Co(en)(2)(NH(2)SC(CH(3))(2)CH(CO(2)H)NH(2)](3+) (IP)) have been studied. The reaction proceeds by nucleophilic attack at sulfur with cleavage of the N-S bond to form a disulfide and leave a coordinated NH(3) ligand. The kinetics (pH 4-10) reveal that the deprotonated thiol, RS(-), is the reactive nucleophile and that the N-deprotonated sulfenamide complex is unreactive. The reactions of IP are approximately 10(4) times slower than those of IA or IC, and the reasons and consequences of this large steric effect are discussed. It is concluded, on the basis of these and other observations from the literature, that there will be substantial steric retardation to nucleophilic attack at two-coordinate sulfur in a R-C(CH(3))(2)-S-X-R' unit because of the regiospecificity of the reaction. The acid dissociation constants of IP and the X-ray structure of its bromide salt also are reported.
Sisley
Margaret J
MJ
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
Ferguson
Michael J
MJ
Jordan
Robert B
RB