The Enthalpy of Insertion of Sulfur into the Metal−Hydrogen Bond. Synthetic, Structural, and Calorimetric Study of the Complexes HS−M(CO)₃C₅R₅ [M = Cr, Mo, W; R = H, Me]

Abstract

Synthetic and calorimetric studies of the sulfhydryl complexes HS-M(CO)(3)C(5)R(5) (M = Cr, R = Me; M = Mo, W, R = H, Me) are reported. The Mo and W complexes can be obtained in high yield by reaction of the hydrido complexes H-M(CO)(3)C(5)R(5) with Ph(3)Sb=S, which readily undergoes single S atom transfer to the metal-hydrogen bond yielding the metal-sulfhydryl complex. Direct reaction between the metal hydrides and a limited amount of sulfur also yields the sulfhydryl complexes as the dominant organometallic product. At sulfur atom/metal hydride ratios higher than 1/1, additional products formulated as HS(n)()-M(CO)(3)C(5)R(5) are detected. The enthalpies of insertion of sulfur from Ph(3)Sb=S and S(8) into the metal-hydrogen bond have been determined by solution calorimetry. The HS-M(CO)(3)C(5)R(5) complexes (M = Mo, W) are readily desulfurized by PCy(3) for R = H, but not for R = Me. The M-SH bond strength estimates for the complexes HS-M(CO)(3)C(5)Me(5) increases in the order Cr (46) < Mo (55) < W (63) (kcal/mol). The HS-Mo(CO)(3)C(5)Me(5) group has a pK(a) value at least 4 pK(a) units less acidic than that of H-Mo(CO)(3)C(5)Me(5). The crystal structure of HS-W(CO)(3)C(5)Me(5) is reported.