Heats of reaction of HMo(CO)(3)(C(5)R(5)) (R=H, CH3) with diphenyldisulfide and of formation of the clusters [PhSMo(CO)(x)(C5H5)](2), x=1,2 : thermodynamic study of molybdenum-sulfur bond strengths

The enthalpies of reaction of HMo(CO)(3)C(5)R(5) (R=H, CH3) with diphenyldisulfide producing PhSMo(CO)(3)C(5)R(5) and PhSH have been measured in toluene and THF solution (R=H, Delta H=-8.5+/-0.5 kcal mol(-1) (tol), -10.8+/-0.7 kcal mol(-1) (THF); R=CH3, Delta H= -11.3 +/- 0.3 kcal mol(-1) (tol), -13.2+/-0.7 kcal mol(-1) (THF)). These data are used to estimate the Mo-SPh bond strength to be on the order of 38-41 kcal mol(-1) for these complexes. The increased exothermicity of oxidative addition of disulfide in THF versus toluene is attributed to hydrogen bonding between thiophenol produced in the reaction and THF. This was confirmed by measurement of the heat of solution of thiophenol in toluene and THF. Differential scanning calorimetry as well as high temperature calorimetry have been performed on the dimerization and subsequent decarbonylation reactions of PhSMo(CO)(3)Cp yielding [PhSMo(CO)(2)Cp](2) and [PhSMo(CO)Cp](2). The enthalpies of reaction of PhSMo(CO)(3)Cp and [PhSMo(CO(2)Cp](2) with PPh(3), PPh(2)Me and P(OMe)(3) have also been measured. The disproportionation reaction: 2[PhSMo(CO)(2)Cp](2)-->2PhSMo(CO)(3)Cp+[PhSMo(CO)Cp](2) is reported and its enthalpy has also been measured. These data allow determination of the enthalpy of formation of the metal-sulfur clusters [PhSMo(CO)(n)C5H5](2), n=1, 2.

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