Protonation of a Biologically Relevant Cu^II μ‐Thiolate Complex: Ligand Dissociation or Formation of a Protonated Cu^I Disulfide Species?

Abstract

The proton-induced electron-transfer reaction of a Cu(II) μ-thiolate complex to a Cu(I) -containing species has been investigated, both experimentally and computationally. The Cu(II) μ-thiolate complex [Cu(II) 2 (L(Me) S)2 ](2+) is isolated with the new pyridyl-containing ligand L(Me) SSL(Me) , which can form both Cu(II) thiolate and Cu(I) disulfide complexes, depending on the solvent. Both the Cu(II) and the Cu(I) complexes show reactivity upon addition of protons. The multivalent tetranuclear complex [Cu(I) 2 Cu(II) 2 (LS)2 (CH3 CN)6 ](4+) crystallizes after addition of two equivalents of strong acid to a solution containing the μ-thiolate complex [Cu(II) 2 (LS)2 ](2+) and is further analyzed in solution. This study shows that, upon addition of protons to the Cu(II) thiolate compound, the ligand dissociates from the copper centers, in contrast to an earlier report describing redox isomerization to a Cu(I) disulfide species that is protonated at the pyridyl moieties. Computational studies of the protonated Cu(II) μ-thiolate and Cu(I) disulfide species with LSSL show that already upon addition of two equivalents of protons, ligand dissociation forming [Cu(I) (CH3 CN)4 ](+) and protonated ligand is energetically favored over conversion to a protonated Cu(I) disulfide complex.

Coordination of new disulfide ligands to CuI and CuII: Does a CuII μ-thiolate complex form?

“…These ligands show similarities to the ligand LSSL, that has been shown to form a stable Cu II l-thiolate complex when reacted with Cu I (Fig. 1) [15,16].…”

Catalytic catechol oxidation by copper complexes: development of a structure–activity relationship

“…Addition of a methyl group next to the sulfur in the disulfide bond, however, results in significantly higher activity (entries [3][4][5][6]. Changing the bridge between the tertiary amine and the pyridyl groups from a methylene to an ethylene spacer at two positions leads to an increase in activity (entry 3 vs. 8), but at four positions it leads to a dramatic decrease in activity (entry 3 vs. 9).…”

“…After evaporation of the solvent, the product was treated with NaOH (50 mL; 5 M) and the aqueous layer was extracted with CHCl 3 (3 × 25 mL). The organic fractions were combined, dried over MgSO 4 8.0 mmol) and propylene sulfide (0.94 mL, 12.0 mmol) was stirred in 20 mL CH 3 CN at reflux temperature for 18 h under Ar atmosphere. The solvent was evaporated, after which the resulting oil was dissolved in 20 mL tetrahydrofuran.…”

“…The layers were separated and the aqueous layer was extracted two more times with 20 mL CH 2 Cl 2 . The combined organic layers were dried over Na 2 SO 4 …”

“…[1][2][3][4][5][6] It has been reported that small changes in the ligand structure can direct the reaction with copper salts towards the formation of either a Cu II µ-thiolate or a Cu I disulfide complex and that these species can interconvert (Fig. 1a).…”