Date of Award

8-1-1989

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

The purpose of this work is to increase the understanding of trapping reactions between metal radicals and organosulfur compounds and of the chemical reactivity pathways available to the tungsten thiolate ($-$SR) compounds formed by these reactions. This information may aid in design of catalytic cycles which utilize soluble transition metal complexes for desulfurization of petroleum feedstocks.Chapter One includes an introduction to inorganic photochemistry, a summary of the photochemical behavior of (CpM(CO)$\sb3$) $\sb2$ (M = Cr, Mo, W) and the primary photoprocesses of CpM(CO)$\sb3$Y, where Y = halogen, alkyl or aryl, and hydride. A short discussion of catalytic desulfurization and a statement of the research problem is also presented.Chapter Two describes the visible light-induced reaction of (CpW(CO)$\sb3$) $\sb2$ and aryl mercaptans to form CpW(CO)$\sb3$H and CpW(CO)$\sb3$SR (R = 2-benzothiazolyl, 2-pyridyl, p-NO$\sb2$C$\sb6$H$\sb4$, p-NH$\sb2$C$\sb6$H$\sb4$, p-CH$\sb3$C$\sb6$H$\sb4$, C$\sb6$H$\sb5$). Quantitative measurements of the quantum yield for disappearance of (CpW(CO)$\sb3$) $\sb2$ and for the quantum yield of appearance for CpW(CO)$\sb3$SR illustrate that the photoreaction is very efficient ($\Phi\sb{\rm D}$ $\sim$ $-$0.35). A mechanism for this reaction is also proposed.Chapter Three demonstrates that UV irradiation of CpW(CO)$\sb3$SR (R = phenyl, tolyl) results in formation of the thiolate-bridged dimers (CpW(CO)$\sb2$SR) $\sb2$. Thermal reactions of CpW(CO)$\sb3$SR allow synthesis of (CpW(CO)SR) $\sb2$. Careful monitoring of these reactions indicates that the monocarbonyl dimers arise from CO-loss reactions of (CpW(CO)$\sb2$SR) $\sb2$. Spectroscopic correlations allow assignment of correct molecular formulas to tungsten carbonyl thiolate-bridged dimers. Dimerization of the unsaturated intermediate can be prevented by trapping with PPh$\sb3$; specifically, the reaction between CpW(CO)$\sb3$STol and PPh$\sb3$ stereospecifically forms cis-CpW(CO)$\sb2$(PPh$\sb3$)STol.Chapter Four describes the reaction between MCPBA (m-chloroperoxybenzoic acid) and a wide variety of CpW(CO)$\sb3$SR compounds. This reaction is a superior method for preparation of sulfinato-S ($-$S(O)$\sb2$R) compounds of tungsten. Additionally, reaction of MCPBA with CpW(CO)$\sb2$(PPh$\sb3$)STol is an efficient method for synthesizing CpW(CO)$\sb2$(PPh$\sb3$)S(O)$\sb2$Tol. Photolyses of CpW(CO)$\sb3$SO)$\sb2$R, both by itself and in the presence of PPh$\sb3$, indicate the importance of carbonyl loss, although the latter reaction unexpectedly yields CpW(CO)$\sb2$(PPh$\sb3$)SR instead of the simple substitution product CpW(CO)$\sb2$(PPh$\sb3$)S(O)$\sb2$R.

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