Reactions of Ph₃Sb=S with copper(I) complexes supported by N-donor ligands: Formation of stable adducts and S-transfer reactivity

In the exploration of sulfur-delivery reagents useful for synthesizing models of the tetracopper-sulfide cluster of nitrous oxide reductase, reactions of Ph₃Sb=S with Cu(I) complexes of N,N,N′,N′-tetramethyl- 2R,3-R-cyclohexanediamine (TMCHD) and 1,4,7-trialkyltriazacyclononanes (R ₃tacn; R = Me, Et, iPr) were studied. Treatment of [(R ₃tacn)Cu(NCCH₃)]SbF₆ (R = Me, Et, or iPr) with 1 equiv of S=SbPh₃ in CH₂Cl₂ yielded adducts [(R₃tacn)Cu(S=SbPh₃)]SbF₆ (1-3), which were fully characterized, including by X-ray crystallography. The adducts slowly decayed to [(R₃tacn)₂Cu₂(μ- η²:η²-S₂)]²⁺ species (4-6) and SbPh₃, or more quickly in the presence of additional [(R ₃tacn)Cu(NCCH₃)]SbF₆ to 4-6 and [(R ₃tacn)Cu(SbPh₃)]SbF₆ (7-9). The results of mechanistic studies of the latter process were consistent with rapid intermolecular exchange of S=SbPh₃ between 1-3 and added [(R ₃tacn)Cu(NCCH₃)]SbF₆, followed by conversion to product via a dicopper intermediate formed in a rapid pre-equilibrium step. Key evidence supporting this step came from the observation of saturation behavior in a plot of the initial rate of loss of 1 versus the initial concentration of [(Me₃tacn)Cu(NCCH₃)]SbF₆. Also, treatment of [(TMCHD)Cu(CH₃CN)]PF₆ with S=SbPh₃ led to the known tricopper cluster [(TMCHD)₃Cu₃(μ₃-S) ₂](PF₆)₃ in good yield (79%), a synthetic procedure superior to that previously reported.