Beiträge zur Chemie der Pseudohalogenide des Tellurs

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.