Preparation and structural characterization of bis ( trimethylsilylmethyl ) tellurium diiodide

The telluroether Te[CH2Si(CH3)3]2 (1) has been prepared in a good yield by the reaction of Na2Te and ClCH2SiMe3 in aqueous solution. The reaction of 1 with I2 affords TeI2[CH2Si(CH3)3]2 (2). The compounds have been characterized by C{H}and TeNMR spectroscopy. The crystal structure of 2 shows the presence of weak Te···I and I···I secondary bonding interactions leading to the formation of a supramolecular assembly.


Introduction
Diorganyl tellurides form a well-known class of compounds. 1Dialkyl tellurides can be prepared by alkylation of Na 2 Te with an alkylhalide. 2The direct reaction of a dialkyltelluride and iodine yields dialkyltellurium diiodides. 3In this type of molecules, tellurium atom displays a pseudo-trigonal bipyramidal coordination geometry where the alkyl groups and the tellurium lone-pair occupy the equatorial positions while the iodine atoms lie at the axial positions. 3,4 urthermore, tellurium usually interacts with neighbouring iodine atoms through secondary bonding interactions, leading to supramolecular associations. 5It has also been reported that, depending on the nature of the alkyl groups, other secondary interactions may be present. 6erein we report the synthetic details and 13 C{ 1 H}-and 125 Te-NMR spectroscopic data of Te[CH 2 Si(CH 3 ) 3 ] 2 (1) and TeI 2 [CH 2 Si(CH 3 ) 3 ] 2 (2).The X-ray single crystal structure analysis of 2 is also reported.

Results and Discussion
Bis(trimethylsilylmethyl)telluride (1) was synthesized in a high yield by treating ClCH 2 SiMe 3 with Na 2 Te prepared from the reduction of elemental tellurium by the aqueous alkaline solution of NaBH 4 .Compound 1 is an orange liquid, which can be stored at low temperatures for several months.Although elemental tellurium and tellurium oxides are rapidly formed, 7 pure 1 can easily be obtained by removing the precipitations by filtration.A direct reaction of 1 with iodine affords 2.
13 C{ 1 H}-NMR spectrum of 1 exhibits two singlets at -3 ppm (CH 3 ) and at -16 ppm (CH 2 ). 13C{ 1 H}-NMR spectrum of 2 resembles that of 1 with the high frequency shift of the signals caused by the presence of iodine atoms.Consistently, the 125 Te chemical shift of 2 (660 ppm) also appears significantly to high frequency with respect to that of 1 (26 ppm).

Crystal structure of 2
The molecular structure and the numbering of the atoms of 2 is shown in Fig. 1.Selected bond distances and bond angles are shown in Table 1.

Synthesis of Te[CH 2 Si(CH 3 ) 3 ] 2 (1). 7
A suspension of tellurium powder (0.642 g; 5.032 mmol) and NaBH4 (0.479 g; 12.661) in 10 ml of 20% aqueous NaOH was refluxed under a nitrogen atmosphere for 3 h, giving during the first 30 minutes an intense violet colour solution which subsequently turned into a pale yellow solution of Na 2 Te.The deaerated solution of ClCH 2 Si(CH 3 ) 3 (1.244g; 10.143 mmol) in 10 ml of methanol was added to the reaction mixture and refluxed for 20 h.The alcohol was distilled off and the residual solution was extracted with three 7.5 ml portions of diethyl ether (or n-hexane).The combined extracts were washed with water and dried over MgSO 4 , and the solvent was removed upon vacuum distillation, giving a pale orange liquid 1 (1.42 g; 94 %).δC -3.460 (s, SiMe3), -15.795 (s, CH2); δTe 25.673 (s).

NMR spectroscopy
13 C{ 1 H} and 125 Te-NMR spectra were recorded on a Bruker DPX400 spectrometer operating at 100.61, and 126.28 MHz, respectively.The respective spectral widths were 20.16 and 126.58 kHz.The pulse widths were 4.00 and 10.00 µs, respectively. 13C{ 1 H} pulse delay was 3.00 s and that for 125 Te was 1.60 s. 13

X-ray crystallography
Diffraction data of 2 were collected on a Nonius Kappa-CCD diffractometer using graphite monochromated Mo-K α radiation (λ = 0.71073 Å; 55 kV, 25 mA).Crystallographic data of 2 are given in Table 2.The structure was solved by direct methods using SIR-92 12 and refined using SHELXL-97. 13After the full-matrix least-squares refinement of the non-hydrogen atoms with anisotropic thermal parameters, the hydrogen atoms were placed in calculated positions in methyl groups (C-H = 0.98 Å) and in the CH 2 groups (C-H = 0.99 Å).The scattering factors for the neutral atoms were those incorporated with the programs.

Fig. 2
Fig.2The packing of the molecules of 2.
C{1 H} accumulations contained ca.50000 transients and those of 125 Te 30000 transients.Tetramethylsilane was used as an internal standard and a saturated solution of Ph 2 Te 2 in CDCl 3 was used as external standard for 125 Te.Chemical shifts (ppm) are reported relative to Me 4 Si, and to neat Me 2 Te [δ (Me 2 Te) = δ (Ph 2 Te 2 ) + 422].11

5 Table 2
Details of the structure determination of 2