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]

Synthetic and calorimetric studies of the sulfhydryl complexes HS−M(CO)3C5R5 (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)3C5R5 with Ph3Sb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)3C5R5 are detected. The enthalpies of insertion of sulfur from Ph3SbS and S8 into the metal−hydrogen bond have been determined by solution calorimetry. The HS−M(CO)3C5R5 complexes (M = Mo, W) are readily desulfurized by PCy3 for R = H, but not for R = Me. The M−SH bond strength estimates for the complexes HS−M(CO)3C5Me5 increases in the order Cr (46) < Mo (55) < W (63) (kcal/mol). The HS−Mo(CO)3C5Me5 group has a pK a value at least 4 pK a units less acidic than that of H−Mo(CO)3C5Me5. The crystal structure of HS−W(CO)3C5Me5 is reported.