Room‐temperature carbon–sulfur bond formation from Ni(II) σ‐aryl complex via cleavage of the S–S bond of disulfide moieties

The formation of ArSY (Y: C(= S)NMe2, Ph, P(= O)(OEt)2) by reductive elimination from σ‐aryl complexes (M(PPh3)2PhBr, M = Ni, Pd), associated with disulfides (YS−SY, Y: C(=S)NMe2 (1), Ph (2), P(=O)(OEt)2 (3)), at ambient temperature, has been investigated. Various mechanistic features of disulfide bond (S−S) cleavage have been elucidated using disulfide 1 by 31P NMR spectroscopy and matrix‐assisted laser desorption/ionization–time of flight mass spectrometric investigations. Based upon the results of nucleophilic cleavage of the S−S bond by PPh3, studies of the reductive elimination process show that when M(PPh3)2PhBr is mixed with disulfide 1, competitive reactions occur between the PPh3 ligand, disulfide 1 and a trace amount of water, leading to low C−S coupling yields; an oxidation reaction of PPh3 with disulfide and water occur prior to C−S cross‐coupling, and phosphonium ion intermediates are likely involved. However, when the disulfide 1 is pretreated with PPh3, the Ni(II) σ‐aryl complex affords the C−S coupling product nearly quantitatively at room temperature. The pretreatment method is also effective for the coupling reaction of disulfide 2 and Ni(II) σ‐aryl complex. The difference between Ni(II) and Pd(II) σ‐aryl complexes on C−S bond formation by reductive elimination can be explained by the affinity of metal for the thiolate ligands derived from the cleaved disulfide.