Zinc polysulfides as precursors to zinc sulfide and as group transfer reagents

Verma, Atul Kumar

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Description

Title

Zinc polysulfides as precursors to zinc sulfide and as group transfer reagents

Author(s)

Verma, Atul Kumar

Issue Date

1996

Doctoral Committee Chair(s)

Rauchfuss, Thomas B.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Chemistry, Inorganic
• Engineering, Materials Science

Language

eng

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.

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Copyright 1996 Verma, Atul Kumar

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