Title

Thermodynamic and kinetic studies of group VI metals with sulfur compounds and/or nitric oxide

Date of Award

1999

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Carl D. Hoff, Committee Chair

Abstract

·Cr(CO)3C5Me5 is a stable 17-electron radical that undergoes oxidative addition with MeSSMe to produce the corresponding chromium thiolate, MeS-Cr(CO)3C5Me5. Unlike reaction with PhSSPh, reaction of ·Cr(CO)3C5Me 5 with MeSSMe proceeds by a third-order mechanism going through a termolecular transition state in which the stronger sulfur-sulfur bond in the alkyl disulfide is attacked simultaneously by two chromium radicals. The rate of this reaction was measured at various temperatures and activation parameters were calculated. The bond strength of MeS-Cr(CO)3C5Me5 was also measured. Results are compared to previous work with PhSSPh and thiols.Enthalpies of reaction of phosphines with sulfur, selenium, and tellurium were measured, as well as desulfurization of triphenylarsenic sulfide, triphenylantimony sulfide, and benzyl trisulfide. These data are used to establish a range of enthalpies of S atom transfer in these compounds which spans 31 kcal/mol from S = SbPh3 to S = PCy3. Such information is needed to determine the enthalpy of formation of sulfhydryl complexes LnM-SH. It was found that complexes H-M(CO)3C5R5 (M = Cr, Mo, W; R = H, Me), as well as Fu1valeneW2(CO)6(H) 2, readily undergo single S atom transfer to the metal-hydrogen bond yielding the metal-sulfhydryl complexes. Synthetic and calorimetric studies were completed and the crystal structures of HS-W(CO)3C5Me 5, FulvaleneW2(CO)6(SH)2, and (Fulvalene)W(CO) 6(mu-S) are reported.In comparison to earlier work with ·Cr(CO)3 C5Me5 and thiols, reaction of ·Cr(CO) 3C5Me5 with H2S yielding HCr(CO) 3C5Me5, HSCr(CO)3C5Me 5, and C5Me5(CO)2Cr=S=Cr(CO)2 C5Me5 was studied. In the presence of a large excess of H2S. the first products of oxidative addition, HCr(CO) 3C5Me5 and HSCr(CO)3C5Me 5, are cleanly formed, and the rate of this first step has been studied as a function of hydrogen sulfide concentration and carbon monoxide pressure. In the absence of added CO, an overall second order rate law is obeyed, yet as the pressure of CO is increased, however, the rate of reaction slows down and at Pco > 10 atm., reaction of hydrogen sulfide obeys a third order rate law (second order in chromium radical). These results are compared to earlier studies of the rates of reaction of thiols, disulfides, and hydrogen with the chromium radical.C5Me5Cr(CO)2(NO) is a stable 18-electron complex that is rapidly formed by the reaction of nitric oxide with ·Cr(CO) 3C5Me5 The heat of this reaction was measured and the C5Me5(CO)2Cr-NO bond strength is presented. This is the first M-NO bond strength ever to be measured. Reductive elimination of nitrosothiols (RSNO) and nitroxyl (HNO) in reactions of metal complexes with NO is also discussed. The crystal structures of W(Phen)(CO) 2(Sph)2 and W(phen)(CO)2(toluene-3,4-dithiolate) are reported.

Keywords

Chemistry, Inorganic; Chemistry, Physical

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9934209