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Schwab, Ingo (2005): Beiträge zur Chemie der Pseudohalogenide des Tellurs. Dissertation, LMU München: Faculty of Chemistry and Pharmacy
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Abstract

This thesis focuses on the experimental and theoretical investigation of tellurium pseudohalides, especially azides. Tellurium tetraazide, Te(N3)4, was prepared directly from TeF4 with Me3SiN3 as an extremely sensitive solid; and azidation of pentafluorotellurate(iv) TeF5- gave the pentaazidotellurate(iv) anion. The crystal structure of the pyridinium salt [pyH][Te(N3)5] consists of [Te(N3)5]- units, considerably distorted from ideal square pyramidal symmetry and linked by Te-N interactions between two anions. The labile tellurium cyanide species Te(CN)2 and Te(CN)4 have been prepared by treatment of tellurium(iv) tetrahalides with cyanide. Both are thermosensitive solids and in addition, the tetracyanide was found to be pyrophoric. Fluorination of R2Te (R = 2,4,6-Me3C6H2 (= Mes), 2,4,6-iPr3C6H2 (= Trip)) with xenon difluoride afforded the sterically demanding diorganotellurium(iv) difluorides R2TeF2. The reaction of R2TeF2 (R = Me, Ph, Mes, Trip) with trimethylsilyl cyanide resulted in the formation of either R2Te(CN)2 (R = Ph, Mes) or the tellanes R2Te (R = Me, Trip). The crystal structure of Te(CN)2, a binary tellurium cyanide and (Mes2TeCN)2O have been determined. All structures of Te(CN)2, Te(CN)4, and Te(CN)6 have been calculated at various levels of theory. The perfluoroaryl tellurolates C6F5TeLi and 4-CF3C6F4TeLi were prepared. These intermediates were identified by NMR spectroscopy and may form, depending on the reaction conditions, either the corresponding ditellanes (C6F5Te)2 and (4-CF3C6F4Te)2 by subsequent oxidation, or a telluranthrene (C6F4Te)2 depending on the reaction conditions. The halogenation products of (C6F4Te)2, (C6F4Te)2F4, (C6F4Te)2Cl4, (C6F4Te)2Br4, as well as the azidation product (C6F4Te)2(N3)4 were synthesized. Furthermore, in pursuit of our recent work on tellurium azides, the syntheses and properties of R2Te(N3)2 (R = CF3, C6F2H3) and RTe(N3)3 (R = CF3 and C6F5) are reported. The crystal structures of (CF3C6F4Te)2, (C6F4Te)2Br4, and (C6F2H3)2Te(N3)2 were determined. The reaction of azide with organotellurium(vi) halides Ph5TeBr and (biphen)2TeF2 (biphen = 2,2'-biphenyldiyl) resulted in the formation and isolation of Ph5TeN3 and (biphen)2Te(N3)2, which are the first tellurium(vi)-pseudohalide species. In addition to spectroscopic data, both crystal structures have been determined. Furthermore, the stability of possible Te(vi) species with higher azide contents PhxTe(N3)6-x and MexTe(N3)6-x as well as the syntheses and properties of their Ph/MexTeFy precursors were investigated, including the crystal structure determination of trans-Ph2TeF4. Ab initio and density functional studies of all molecules regarding the structures and electronic populations were performed. The first tellurium compounds containing the extremely bulky tris(phenyldimethylsilyl)methyl (Tpsi) and 2,6-bis(2,4,6-tri{isopropylphenyl)phenyl (2,6-Trip2C6H3) moieties have been synthesized and isolated. Careful oxidation of the tellurolate TpsiTeLi resulted in the formation of the crowded ditellane (TpsiTe)2; subsequent iodination gave the alkanetellurenyl iodide TpsiTeI. In a similar fashion, the terphenyl substituted ditellane (2,6-Trip2C6H3Te)2 and the arenetellurenyl iodide 2,6-Trip2C6H3TeI were prepared. Reaction of the tellurenyl iodides TpsiTeI, 2,6-Trip2C6H3TeI, as well as TripTeI, Mes*TeI and the donor-stabilized 2-Me2NCH2C6H4TeI with AgN3 resulted in the formation and isolation of the corresponding tellurenyl azides TpsiTeN3, TripTeN3, Mes*TeN3, 2,6-Trip2C6H3TeN3, and 2-Me2NCH2C6H4TeN3. Furthermore, the tris(ethyldimethylsilyl)methyl (Tesi) tellurium compounds (TesiTe)2, TesiTeI, and TesiTeN3 have been prepared, but could not be isolated in pure form. The crystal structures of TpsiTeLi, (TpsiTe)2, TpsiTeN3, 2,6-Trip2C6H3TeI, 2,6-Trip2C6H3TeN3, and 2-Me2NCH2C6H4TeN3 have been determined by X-ray diffraction. Additionally, computational studies of the molecules for which experimental structural data were available, were performed.