DONOR SOLVENT MEDIATED REACTIONS OF ELEMENTAL ZINC AND SULFUR, SANS EXPLOSION

The reactions of zinc powder with solutions of elemental sulfur in various donor solvents is described. Complexes of the type ZnS6(N-donor)(2) 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 (DMAP > MeIm > TMEDA > pyridine) parallel the basicity of the ligands. The TMEDA complex crystallizes in the monoclinic space group C2/c with a = 12.255(3) Angstrom, b = 10.559(2) Angstrom, c = 12.392(2) Angstrom, and beta = 110.22(2)degrees. In the solid state ZnS6(TMEDA) adopts a tetrahedral geometry with a seven-membered ZnS6 ring. A variety of reactivity studies were conducted on ZnS6(TMEDA). Solutions of ZnS6(TMEDA) undergo Ligand exchange with quinuclidine and MeIm to afford ZnS(6)L(2) (L = MeLm, quinuclidine). The anionic species [ZnS12](2-) is formed upon addition of (PPh(4))(2)S-6 to ZnS6(TMEDA). Optical and reactivity studies showed that MeIm, but not pyridine, displaces the polysulfide from ZnS6(MeIm)(2) as indicated by the appearance of the chromophore S-3(-). ZnS6(TMEDA) reacts with the electrophilic acetylenes dimethyl acetylenedicarboxylate and methyl propiolate to give the dithiolene complexes ZnS(2)C(2)Ri(CO(2)Me)(TMEDA) {R = CO(2)Me, H}. Solid ZnS6(TMEDA) cleanly decomposes at 350 degrees C as indicated by TGA studies. Preparative scale conversions at 500 degrees C affords cubic ZnS. Submicron cubic ZnS is generated upon partial desulfurization of ZnS6(TMEDA) with tertiary phosphines as established by electron microscopic studies.