Synthesis, Characterization, and Reactivity of a Synthetic End-On Cobalt(II) Alkyl Persulfide Complex as a Model Platform for Thiolate Persulfidation

Abstract

Persulfides (RSS − ) are ubiquitous source of sulfides (S 2− ) in biology, and interactions between RSS − and bioinorganic metal centers play critical roles in biological hydrogen sulfide (H 2 S) biogenesis, signaling, and catabolism. Here, we report the use of contact-ion stabilized [Na(15-crown-5)][ t BuSS] (1) as a simple synthon to access rare metal alkyl persulfide complexes and to investigate the reactivity of RSS − with transition metal centers to provide insights into metal thiolate persulfidation, including the fundamental difference between alkyl persulfides and alkyl thiolates. Reaction of 1 with [Co II (TPA)(OTf)] + afforded the η 1 -alkyl persulfide complex [Co II (TPA)(SS t Bu)] + (2), which was characterized by X-ray crystallography, UV−vis spectroscopy, and Raman spectroscopy. RSS − coordination to the Lewis acidic Co 2+ center provided additional stability to the S−S bond, as evidenced by a significant increase in the Raman stretching frequency for 2 (v S−S = 522 cm −1 , Δv S−S = 66 cm −1 ). The effect of persulfidation on metal center redox potentials was further elucidated using cyclic voltammetry, in which the Co 2+ → Co 3+ oxidation potential of 2 (E p,a = +89 mV vs SCE) is lowered by nearly 700 mV when compared to the corresponding thiolate complex [Co II (TPA)(S t Bu)] + (3) (E p,a = +818 mV vs SCE), despite persulfidation being generally seen as an oxidative post-translational modification. The reactivity of 2 toward reducing agents including PPh 3 , BH 4 − , and biologically relevant thiol reductant DTT led to different S 2− output pathways, including formation of a dinuclear 2Co−2SH complex [Co II 2 (TPA) 2 (μ 2 -SH) 2 ] 2+ (4).

Generation of Thiosulfate, Selenite, Dithiosulfite, Perthionitrite, Nitric Oxide, and Reactive Chalcogen Species by Binuclear Zinc(II)-Chalcogenolato/-Polychalcogenido Complexes

“…On the other hand, persulfide scrambling and the action of glutathione reductase are responsible for the production of GSSH and inorganic dihydropolysulfide species. ,, Moreover, polysulfide signal transduction is believed to be driven by H 2 S/HS – mediated sulfuration of sulfenylated thiol residues and various electrophilic species available in proteins. ,,, Bioavailable sulfur is believed to be supplied to the mammals and many bacteria by a small fraction of persulfidated proteome in these organisms. − Transpersulfidation is also an important process for obtaining the sulfur atom in many persulfidated proteins . In connection to the thiol persulfidation process, Pluth and co-workers have very recently put forward the synthesis and reactivity of a mononuclear Co(II)-η 1 - t butylpersulfide complex …”