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,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 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 [(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).