ASCERTAINING THE ROLES OF EACH METAL IN THE ACTIVATION OF S-H BONDS IN HYDROGEN-SULFIDE AND THIOLS BY THE HETEROBINUCLEAR COMPLEX [RHRE(CO)4(PH2PCH2PPH2)2]

The reactions of H2S, HSEt, and HSPh with [RhRe(CO)4(dppm)2] have been studied. These reactions are facile at ambient temperature, yielding [RhRe(CO)4(μ-S)(dppm)2] (2) in the case of H2S and [RhRe(CO)3(μ-H)(μ-SR)(dppm)2] (R = Et (5) Ph (6)) for the thiols. Monitoring these reactions at −80 °C by 31P, 13C, and 1H NMR spectroscopy indicates that in all cases the first species is the HSR adduct (R = H, Et, Ph), which then yields [RhRe(CO)4(SR)(μ-H)(dppm)2] via oxidative addition of an S–H bond. In subsequent steps the reactions involving H2S and thiols proceed differently. In the case of H2S, the presumed second S-H oxidative addition step is followed by facile H2 loss, and no additional intermediate is observed before formation of 2, even at −60 °C. For ethanethiol no other intermediate is observed before formation of 5; however, for benzenethiol a tetracarbonyl species, in which the hydride ligand has migrated to Re, is observed after the hydride-bridged species, followed by movement of the thiolate group to the bridging position with concomitant loss of one carbonyl to give 6. Mechanisms for these transformations are proposed. The structure of 5 was determined by X-ray techniques, confirming that the thiolate group and the hydride ligand bridge the metals on opposite faces of the dimer. Compound 5 crystallizes in the monoclinic space group P21/c with a = 12.216 (3) A, b = 19.845 (7) Å, c = 23.316 (7) Å, β = 103.19 (2) Å, V = 5503 Å3, and Z = 4 and has refined to R = 0.049 and Rw = 0.056 on the basis of 370 parameters varied and 5011 independent observations. © 1990, American Chemical Society. All rights reserved.