Redox-Regulated Ethylene Binding to a Rhenium-Thiolate Complex

The influence of oxidation state on the reversibility of carbon-sulfur bond forming reactions between ethylene and [Re(DPPBT)(3)](n+) (n = 0, +1, +2; DPPBT = 2-diphenylphosphinobenzenethiolate) has been investigated. For the neutral complex [Re(DPPBT)(3)], no reaction with ethylene is spectroscopically detectable consistent with the determined equilibrium constant, K-1, of (1.9 +/- 0.4) x 10(-11) M-1. Oxidation by one electron to [Re(DPPBT)(3)](+) yields a stable complex that rapidly and reversibly binds ethylene with electrochemically determined constants of k(f) = (1.2 +/- 0.2) x 10(-1) M-1 s(-1), k(r) = (3.0 +/- 0.4) x 10(-2) s(-1), and K-2 = 4.0 +/- 0.8 M-1. C-S bond formation/cleavage can be regulated by ethylene concentration, and the system is stable to multiple cycles of nitrogen/ethylene purges. Further oxidation to the dication in the presence of ethylene by chemical or electrochemical methods stabilizes the C-S bond, K-3 = (2.5 +/- 0.9) x 10(9) M-1, and the dithioether product has been characterized by X-ray crystallography. The large differences in K as a function of charge permit the controlled binding and release of ethylene as a function of applied potential.