Thiophene Derivatives of Rhenium and Titanium PDF Download

Author: Philip Roy Stafford
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Languages : en
Pages : 320

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Book Description
Significant strides have recently been made involving organometallic modeling of hydrodesulfurization (HDS). These studies have typically utilized late transition metals with high d-electron counts. This thesis focuses on three areas, (i) the synthesis of high oxidation state metal-oxo derivatives of thiophene, (ii) the exploration of the reactivity of the carbon-sulfur bond in condensed thiophenes, and (iii) the discovery of a new polymerization technique for the preparation of polythiophenes. The treatment of thienyllithium with Re(CO)$\sb5$Br followed by PPh$\sb3$ affords the acyl complex cis-$\rm(CO)\sb4(PPh\sb3)Re(C(O)C\sb4H\sb3S).$ A similar pentacarbonyl, $\rm(CO)\sb5Re(C(O)C\sb4H\sb3S),$ complex can be made via the treatment of NaRe(CO)$\sb5$ with thienoylchloride and can be decarbonylated to give $\rm(CO)\sb5Re(C\sb4H\sb3S).$ $\rm(CO)\sb5Re(C\sb4H\sb3S),$ which can be more conveniently made by the treatment of Re(CO)$\sb5$Br with ZnCl$\rm(C\sb4H\sb3S),$ is stable with respect to moisture but decomposes in the presence of strong acids to afford thiophene. Treatment of $\rm ReOCl\sb3(PPh\sb3)\sb2$ with thienyllithium reagents afforded Li(THF)$\rm\sb{n}$,ReO(thienyl)$\sb4$, where thienyl is 2-$\rm C\sb4H\sb3S,$ 2-$\rm MeC\sb4H\sb2,$ 2-$\rm C\sb8H\sb5S$ (benzothienyl), and 2-$\rm C\sb{12}H\sb7S$ (dibenzothienyl). Electrochemical studies demonstrate that these Re(V) complexes undergo oxidation at mild potentials. Crystallographic analyses of $\rm Li(THF)\sb3ReO(C\sb4H\sb3S)\sb4$ and $\rm Li(THF)\sb4ReO(C\sb8H\sb5S)\sb4$ indicate a square pyramidal Re center with the four thienyl ligands tilted in a pinwheel arrangement. The (ReO(thienyl)$\sb4\rbrack\sp{-}$ compounds decompose in the presence of water to give thiophene and oxidatively coupled organic compounds in the presence of oxygen. Attempts at electrophilic substitution at the oxygen with trimethylsilyl chloride afforded 2-$\rm(Me\sb3Si)C\sb4H\sb3S.$ The reaction of 2,2$\sp\prime$-Li(LiS)C$\sb{12}$H$\sb8$ with $\rm(C\sb5H\sb5)\sb2TiCl\sb2$ gave the metallacyclic complex $\rm(C\sb5H\sb5)\sb2TiSC\sb{12}H\sb8$ (1). DNMR studies showed that 1 is stereochemically nonrigid. The structure of the $\rm MeC\sb5H\sb4$ analog of 1 was determined by single crystal X-ray diffraction. Compound 1 decomposes photolytically to yield dibenzothiophene and a $\rm(C\sb5H\sb5)\sb2Ti$ species. An attempt to generate 1 via the double metalation of 2-phenylbenzenethiol with followed by $\rm(C\sb5H\sb5)TiCl\sb2$ gave $\rm(C\sb5H\sb5)\sb2TiS\sb2C\sb{24}H\sb{16}$ (2). Single crystal X-ray diffraction indicated that 2 is a complex of the 2,2$\sp\prime$dimercapto-3,3$\sp\prime$-diphenylbiphenyl (2,2$\sp\prime$-(LiS)$\sb{2}$-3,3$\sp\prime$-$\rm Ph\sb2C\sb{12}H\sb6)$ ligand. Electrochemical studies of the new complexes demonstrated that the Ti$\rm\sp{IV}$ to Ti$\rm\sp{III}$ reduction is reversible. The treatment of thiophene with TiCl$\sb4$/HX (X = OTf, Cl) results in polymerization to generate material having the empirical formula of $\rm C\sb{4n}H\sb{4n}S\sb{n}$, and molecular weights of $\rm M\sb{n}\sim1782$ daltons. NMR and IR studies suggests that the polymer is comprised of a combination of sp$\sp2$ and sp$\sp3$ carbon centers and FAB-MS experiments indicate chain lengths that vary by units of $\rm C\sb4H\sb4S.$ These polymers can coordinate to TiCl$\sb4$ and can be dehydrogenated by quinones. Efforts to polymerize substituted thiophenes afforded oligomers.