Redox-Innocent Metal-Assisted Cleavage of S-S Bond in a Disulfide-Containing Ligand.

Due to their redox capabilities, thiols have an important role in biological oxidative/reductive processes through the formation of disulfides or their oxidation to into sulfenic, sulfinic, or sulfonic derivatives being also relevant for specific enzyme activities. The mechanisms of these biological pathways often involve metal ion(s). In this case, deciphering metal-assisted transformation of the S-S bond is of primary interest. This report details the reactivity of the disulfide-containing 2,6-bis[(bis(pyridylmethyl)amino)methyl]-4-methylmercaptophenyldisulfide (L(Me(BPA)S-S)) ligand with Cu(II) using different experimental conditions (anaerobic, H2O-only, H2O/O2, or O2-only). Crystallographic snapshots show the formation of tetranuclear disulfide, dinuclear sulfinate, and sulfonate complexes. Mechanistic investigations using Zn(II) as control indicate a non-metal-redox-assisted process in all cases. When present, water acts as nucleophile and attacks at the S-S bond. Under anhydrous conditions, a different pathway involving a direct O2 attack at the disulfide is proposed.