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Title:Zinc polysulfides as precursors to zinc sulfide and as group transfer reagents
Author(s):Verma, Atul Kumar
Doctoral Committee Chair(s):Rauchfuss, Thomas B.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Engineering, Materials Science
Abstract:In the first part of the thesis, reactions of zinc powder with solutions of elemental sulfur in various donor solvents are described. Complexes of the type $\rm ZnS\sb6$(N-donor)$\sb2$ are obtained for the ligands tetramethylethylenediamine (TMEDA), N-methylimidazole (MeIm), and 4-(N,N-dimethylamino)pyridine (DMAP). Ligand competition studies on pyridine solutions revealed that the relative stability constants $\rm (DMAP>MeIm>TMEDA>pyridine)$ parallels the basicity of the ligands. Crystallographic analysis shows that $\rm ZnS\sb6$(TMEDA) adopts a tetrahedral geometry with a seven-membered $\rm ZnS\sb6$ ring. Solutions of $\rm ZnS\sb6$(TMEDA) undergo ligand exchange with other ligands L to afford $\rm ZnS\sb6L\sb2$ (L = MeIm, quinuclidine). The pyridine analog, $\rm ZnS\sb6py\sb2$ also undergoes ligand substitution with TEEDA $(N,N,N\prime,N\prime$-tetraethylethylenediamine) and ($-$)-sparteine to afford $\rm ZnS\sb6$(TEEDA) and $\rm ZnS\sb6\{(-)$-sparteine$\};$ these complexes can not be prepared by the reaction of sulfur and zinc dust in TEEDA or ($-$)-sparteine. Optical and reactivity studies showed that MeIm, but not pyridine, displaces the polysulfide from $\rm ZnS\sb6(MeIm)\sb2$ as indicated by the appearance of the chromophore $\rm S\sb3\sp-.$ ZnS$\sb6$(TMEDA) reacts with the electrophilic acetylenes methylpropiolate and dimethylacetylenedicarboxylate (DMAD) to give the dithiolene complexes $\rm ZnS\sb2C\sb2R(CO\sb2Me)$(TMEDA), where R = $\rm CO\sb2Me,$ H.
The second portion of thesis studies the conversion of $\rm ZnS\sb6$(N-donor)$\sb2$ complexes into ZnS and related materials. Solid $\rm ZnS\sb6(TMEDA)$ cleanly decomposes at $350\sp\circ$C to cubic ZnS, as indicated by TGA and preparative scale studies. Submicron cubic ZnS is generated upon partial desulfurization of $\rm ZnS\sb6(TMEDA)$ with tertiary phosphines as established by electron microscopic studies. The reaction of $\rm ZnS\sb6(MeIm)\sb2$ with 5 equiv of zinc dust affords nanosize insoluble material $\rm ZnS(MeIm)\sb{1\sim x}\ (x\approx 0{-}0.3).$ This unusual species, unlike cubic ZnS, is very reactive towards MeIm solutions of sulfur and affords $\rm ZnS\sb6(MeIm)\sb2.$ The TGA, XPS, CL, and SS MAS $\sp{13}$C NMR spectroscopic measurements suggest a strong Zn-MeIm interaction in $\rm ZnS(MeIm)\sb{1\sim x}.$ This species also reacts with $\rm Cu\sb4S\sb{10}(MeIm)\sb4$ to afford $\rm\lbrack Zn(MeIm)\sb6\rbrack\lbrack Cu\sb4S\sb{12}\rbrack.$
In the final Chapter, the species $\rm ZnS\sb6(TMEDA)$ has been developed as a potent polysulfido-transfer reagent. The reaction of this zinc reagent with $\rm Cp\sb2TiCl\sb2$ gives $\rm Cp\sb2TiS\sb5.$ When a $\rm CS\sb2$ slurry of $\rm ZnS\sb6(TMEDA)$ is treated with $\rm Se\sb2Cl\sb2,$ chalcogenospecific formation of 1,2-$\rm Se\sb2S\sb6$ is observed, as confirmed by reverse phase HPLC, Raman, and $\sp{77}$Se NMR spectroscopic measurements. A $\rm CS\sb2$ solution of 1,2-$\rm Se\sb2S\sb6$ is mildly reactive towards UV-photolysis, rearranging to its 1,3-, 1,4-, 1,5-, and other isomers over the course of several hours. The reaction of $\rm CH\sb2Cl\sb2$ solutions of $\rm ZnS\sb6(TMEDA)$ with $\rm TiCl\sb4$ affords a brown solid $\rm TiS\sb{x}.$ Extraction of $\rm TiS\sb{x}$ with MeIm, affords an air-sensitive molecular complex $\rm Ti(S\sb2)\sb2(MeIm)\sb3.$ The crystal structure reveals a pseudo trigonal-bipyramidal geometry around Ti, with the two MeIm ligands bound axially. The oxidation of $\rm TiS\sb4(MeIm)\sb3$ generates a dinuclear $\mu$-oxo species $\rm\lbrack Ti\sb2(S\sb2)\sb2(\mu$-$\rm S\sb2)(\mu$-O)$\rm (MeIm)\sb4\rbrack ,$ as confirmed by single crystal X-ray crystallography.
Issue Date:1996
Rights Information:Copyright 1996 Verma, Atul Kumar
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712470
OCLC Identifier:(UMI)AAI9712470

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