A Bioinspired Disulfide/Dithiol Redox Switch in a Rhenium Complex as Proton, H Atom, and Hydride Transfer Reagent
Shao‐An Hua, Lucas A. Paul, Manuel Oelschlegel, Sebastian Dechert, Franc Meyer, Inke Siewert
Abstract
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 fac-[Re(S–Sbpy)(CO)3Cl] (1, S–Sbpy = [1,2]dithiino[4,3-b:5,6-b′]dipyridine) undergoes two successive reductions at equal potentials of −1.16 V vs Fc+|0 at room temperature forming [Re(S2bpy)(CO)3Cl]2– (12–, S2bpy = [2,2′-bipyridine]-3,3′-bis(thiolate)). 12– has two adjacent thiolate functions at the bpy periphery, which can be protonated forming the S–H···–S unit, 1H–. The disulfide/dithiol switch exhibits a rich PCET reactivity and can release a proton (ΔG°H+ = 34 kcal mol–1, pKa = 24.7), an H atom (ΔG°H• = 59 kcal mol–1), or a hydride ion (ΔG°H– = 60 kcal mol–1) as demonstrated in the reactivity with various organic test substrates.