Dissertations from ProQuest

Title

Thermodynamic and kinetic studies of oxidative addition of thiols and disulfides to chromium radical(carbon monoxide)(3) carbon(5) methyl(5) and tungsten(phenyl)(carbon monoxide)(3) (ethyl cyanide)

1996

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Chemistry

First Committee Member

Carl D. Hoff, Committee Chair

Abstract

The complex $\rm\cdot Cr(CO)\sb3C\sb5Me\sb5$ is a stable radical that undergoes oxidative addition with thiols. The products are H-Cr(CO)$\rm\sb3C\sb5Me\sb5$ and the corresponding chromium thiolate, RS-Cr(CO)$\rm\sb3C\sb5Me\sb5.$ The reaction proceeds through a third order reaction mechanism that involves the formation of a 19-electron complex as the first step. This intermediate then reacts with a second molecule of $\rm\cdot Cr(CO)\sb3C\sb5Me\sb5$ to form the products. The absolute bond strengths of RS-Cr(CO)$\rm\sb3C\sb5Me\sb5$ are reported. The rates of reaction in different temperatures were measured and the activation parameters were calculated. This reaction is accelerated by adding W(phen)(CO)$\sb3$(EtCN) to the reaction solution. The radical $\rm\cdot Cr(CO)\sb3C\sb5Me\sb5$ also undergoes oxidative addition with phenyl disulfide. In this case the reaction proceeds through a second order reaction mechanism because the PhS-SPh bond is much weaker than the PhS-H bond. A free thiyl radical is generated which can then react with $\rm\cdot Cr(CO)\sb3C\sb5Me\sb5$ to form the second molecule of product. The thiyl radical is very reactive and will attack other available complexes. In reactions when excess chromium thiolate was added the rate of reaction was decreased. The reaction between PhSSPh and H-Cr(CO)$\rm\sb3C\sb5Me\sb5$ was also studied. This reaction proceeds through a radical chain mechanism, and without the presence of $\rm\cdot Cr(CO)\sb3C\sb5Me\sb5$ the reaction possibly does not proceed. The absolute bond strength of PhS-Cr(CO)$\rm\sb3C\sb5Me\sb5$ was confirmed by this reaction. The rates of reaction at different temperatures were measured and the activation parameters were calculated. The relative rates of reaction for thiyl radical with $\rm\cdot Cr(CO)\sb3C\sb5Me\sb5,$ H-Cr(CO)$\rm\sb3C\sb5Me\sb5,$ and PhS-Cr(CO)$\rm\sb3C\sb5Me\sb5$ are presented.As a comparison, the oxidative addition of disulfides to W(phen)(CO)$\sb3$(EtCN) was studied. The 18-electron W(phen)(CO)$\sb3$(EtCN) complex reacts with disulfides through coordination. The rates of reaction and the activation parameters are presented. The product W(phen)(CO)$\sb2$(SR)$\sb2$ undergoes thiol/thiolate exchange reactions and reversibly binds CO. The heat of reaction for thiol/thiolate exchange was measured for W(phen)(CO)$\rm\sb2(S\sp{t}Bu)\sb2$ with thiophenol and 3,4-dimercaptotoluene. The bond strength of CO binding is also presented. Mo(phen)CO$\sb3$(EtCN) behaves rather differently to the analogous W(phen)(CO)$\sb3$(EtCN) complex. At different concentrations of disulfide the reaction proceeds through different mechanisms.

Keywords

Chemistry, Inorganic