Proton-Coupled Electron Transfer from Sulfur: A S-H/S-D Kinetic Isotope Effect of ≥31.1

Not bound to a metal and yet still involved in proton-coupled electron transfer—this is the distinguishing property of the sulfur center of the complex [OsIV(tpy)(Cl)2{NS(H)C6H3Me2}]+ (1, tpy=terpyridine). In fact 1 also provides the first example of proton-coupled electron transfer involving a sulfur atom. This reaction is notable for the large magnitude of the kinetic isotope effect.