Reactions of Ph3Sb=S with Copper(I) Complexes Supported by N-Donor Ligands: Formation of Stable Adducts and S-Transfer Reactivity

摘要

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,3R-cyclohexanediamine (TMCHD) and 1,4,7-trialkyltriazacyclononanes (R3tacn; R = Me, Et, iPr) were studied. Treatment of [(R3tacn)Cu(NCCH3)]SbF6 (R = Me, Et, or iPr) with one equivalent 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 [(R₃tacn)Cu(NCCH₃)]SbF₆ to >4–6 and [(R₃tacn)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 [(R₃tacn)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 (Brown, E. C.; York, J. T.; Antholine, W. E.; Ruiz, E.; Alvarez, S.; Tolman, W. B. J. Am. Chem. Soc. >2005, 127, 13752–13753).