A Bioinspired Disulfide/Dithiol Redox Switch in a Rhenium Complex as Proton, H Atom, and Hydride Transfer Reagent.

The transfer of multiple electrons and protons is of crucial importance in many reactions relevant in biology and chemistry. Natural redox-active cofactors are capable of storing and releasing electrons and protons under relatively mild conditions and thus serve as blueprints for synthetic proton-coupled electron transfer (PCET) reagents. Inspired by the prominence of the 2e/2H disulfide/dithiol couple in biology, we investigate herein the diverse PCET reactivity of a Re complex equipped with a bipyridine ligand featuring a unique SH···S moiety in the backbone. The disulfide bond in -[Re(bpy)(CO)Cl] (, bpy = [1,2]dithiino[4,3-:5,6-']dipyridine) undergoes two successive reductions at equal potentials of -1.16 V vs Fc at room temperature forming [Re(bpy)(CO)Cl] (, bpy = [2,2'-bipyridine]-3,3'-bis(thiolate)). has two adjacent thiolate functions at the bpy periphery, which can be protonated forming the S-H···S unit, H. The disulfide/dithiol switch exhibits a rich PCET reactivity and can release a proton (Δ° = 34 kcal mol, p = 24.7), an H atom (Δ° = 59 kcal mol), or a hydride ion (Δ° = 60 kcal mol) as demonstrated in the reactivity with various organic test substrates.