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 center dot center dot center dot S- moiety in the backbone. The disulfide bond in fac-[Re((S-S)bpy)(CO)(3)Cl] (1, (S-S)bpy = [1,2]-dithiino[4,3-b:5,6-b']dipyridine) undergoes two successive reductions at equal potentials of -1.16 V vs Fc(+vertical bar 0) at room temperature forming [Re((S2)bpy)(CO)(3)Cl](2-) (1(2-), (S2)bpy = [2,2'-bipyridine]-3,3'-bis(thiolate)). 1(2-) has two adjacent thiolate functions at the bpy periphery, which can be protonated forming the S-H center dot center dot center dot S- unit, 1H(-). The disulfide/dithiol switch exhibits a rich PCET reactivity and can release a proton (Delta G degrees(+)(H) = 34 kcal mol(-1), pK(a) = 24.7), an H atom (Delta G degrees(center dot)(H) = 59 kcal mol-1), or a hydride ion (Delta G degrees(-)(H) = 60 kcal mol(-1)) as demonstrated in the reactivity with various organic test substrates.