Telvin D. Ju

Reactions of the complexes M(Pr3)2(CO)3(M = Cr, Mo, W; R = iPr, Cy) with thiols, hydrogen sulfide, disulfides, hydrogen iodide and iodine. The role of heteroatoms in determining the metal-hydrogen bond strength at a sterically crowded metal center

Abstract The complexes M(PCy3)2(CO)3 (M = Cr, Mo, W) react with phenyl disulfide to form stable 17-electron radical complexes Ṁ(PCy3)2(CO)3(SPh). Reaction with other alkyl and aryl disuufides also yields stable radicals and reaction with I2 yields Ẇ(P1Pr3)2(CO)3(I). Reaction with thiols, hydrogen sulfide and hydrogen iodide yield the corresponding 18-clectron hydrides W(P1Pr3)2(CO)3(H)(X). The crystal structure of W(P1Pr3)2(CO)3(H)(I) is reported and allows comparison with the structure of the radical complex Ẇ(P1Pr3)2(CO)3(I). The WH bond strengths in these heteroatorn complexes are low, 55–57 kcal mol−1. In spite of steric crowding, H atom transfer from W(P1Pr3)2(CO)3(H)(SPh) to Ċr(CO)2(PPh3)Cp occurs readily due to the stronger nature of the CrH bond formed. The chromium radical does not appear to attack the molecular hydrogen complex W(Pr3)2(CO)3(H2) or its dihydride form W(Pr3)2(CO)n3(H)2 based on rate of hydrogenation studies. Phenyl disulfide does react with either W(Pr3)2(CO)3(H2) a its dihydride tautomer W(Pr3)2(CO)3(H)2 to form thiophenol and W(Pr3)2(CO)3(SPḣ). This reaction is proposed to proceed by reaction of ṠPh radicals which are generated in situ. These studies are used to bracket the first WH bond dissociation energy in W(Pr3)2(CO)3(H)2. Additional studies of H atom and heteoratom transfer are described.

First- and second-order mechanisms for oxidative addition for bound methyl disulfide in the complex W(CO)3(phen)(MeSSMe)

Abstract The rate of oxidative addition of methyl disulfide in the complex W(CO)3(1,10-phenanthroline) (MeSSMe) in methylene chloride has been studied. The dominant reaction pathway is second order in metal complex and inhibited by excess methyl disulfide. Formation of a dinuclear complex [W(CO)3(phen)]2(MeSSMe) is proposed to lead to the transition state for cleavage of the sulfur-sulfur bond in the second-order mechanism. In neat methyl disulfide, or in concentratred solutions of methyl disulfide at low metal complex concentrations, the reaction occurs at reduced rate and follows a first-order mechanism. Addition of Mo(CO)3(1,10-phenanthroline) (MeSSMe) to the corresponding tungsten complex results in a ten-fold increase in the rate of oxidative addition of the tungsten complex and production of Mo(CO)4(1,10-phenanthroline) as the sole molybdenum-containing product. The faster rate of reaction in the presence of the molybdenum complex is attributed to the faster formation of the heteronuclear dinuclear intermediate by initial loss of MeSSMe from the molybdenum versus tungsten center. Additional kinetic/mechanistic studies are described using a new flow-through FT-IR/microscope reaction system designed to allow convenient monitoring of small quantities of sensitive/hazardous reactants.

Heats of reaction of HMo(CO)3(C5R5) (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

Abstract The enthalpies of reaction of HMo(CO) 3 C 5 R 5 (R = H, CH 3 ) with diphenyldisulfide producing PhSMo(CO) 3 C 5 R 5 and PhSH have been measured in toluene and THF solution (R = H, ΔH = −8.5 ± 0.5 kcal mol −1 (tol), −10.8 ± 0.7 kcal mol −1 (THF); R = CH 3 , ΔH = −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 + [PhSMP(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 C 5 H 5 ] 2 , n = 1,2.

Crystallographic and spectroscopic assessment of chelate-stabilized aryl halide complexes at a seven-coordinate d4 molybdenum centre

A new series of chelate stabilized aryl halide coordination complexes of molybdenum are prepared by a novel oxidative addition strategy; quantitative equilibrium measurements suggest that the structure of the chelate ring, rather than the identity of the halide (X = Cl, Br, I), controls the strength of aryl halide binding in these complexes.