Synthesis and Single Crystal X-ray Studies of Cyclic Te(IV) Diiodide

The cyclic tellurium(IV) diiodide, 2-Methyl-1,1-diiodo-1-telluracyclopentane, was prepared in good yields at room temperature by the incorporation of tellurium powder across Carbon–Iodine bond in presence of sodium iodide and acetone. The cyclic tellurium(IV) diiodide compound has been established by proton and 13carbon NMR spectroscopy along with elemental analysis. This compound was further characterized by 125Te NMR in DMSO. Molecular structures of cyclic tellurium(IV) diiodide was also established by single-crystal X-ray studies. In solid-state, molecular structures of cyclic tellurium(IV) diiodidepossess scarcely observed Te…I secondary bonding interactions (SBIs) and two molecule are co-crystallized. Both molecules are interconnected with each other by Te…I secondary bonding interactions. The five-membered rings acquire a twist-boat shape structure. Observed C–Te–C bond angles for molecule A, and molecule B are 85.0(1)°& 85.4(2)° respectively. Similarly observed, I–Te–I bond angles for both molecule A & B are 174.5(1)°&174.2(1)° respectively.

Simultaneously same group have also demonstrated the insertion of in situ prepared ArTeBr, (Ar = Mesityl, Mes; 1-Napthyl, Np) across the C-Br bond of RCOCH2Br, (R = t-Bu, Et2N, 2-Furon, 2-Thiophene, 2,5-Me2Thiophene) to get unsymmetrical Ar(RCOCH2)TeBr2 derivatives (7a-7j) [16,18,[20][21][22] On the basis of these observations, we envisaged that the without functional group alkyl halide can also react with elemental tellurium at room temperature in presence of NaI and acetone. Since liquid state ligands with sodium iodide are capable of inserting Te(0) across C-Br/I bond at room temperature. With these ideas, we have chosen the ligands 1,4-dibromopentane. Herein, we report the synthesis and single crystal x-ray studies of cyclic chiral center bearing tellurium(IV) diiodide.

Result and Discussion
The cyclic tellurium(IV) diiodidewas prepared in excellent yield at room temperature by treatment of tellurium powder with 1,3-dibromopropane in presence of sodium iodide and acetone.The molecule was isolated as bright red powdered solids.The powder cyclic tellurium(IV) diiodide was dissolve in chloroform and allow to slow evaporation to give rise a red needle shaped crystal. The cyclic tellurium(IV) diiodide has been characterized by l H, 13 C, 125 Te NMR spectroscopy, and elemental analysis. Molecular structure was further confirmed by single-crystal X-ray studies (vide infra). The 1 H NMR spectrum of the molecule reveal the CH3 proton as a doublet with a coupling constant of 5.6 Hz, & six sets of multiplets for the three methylene and one CH protons.Its 13 C NMR spectrum shows the following 5 peaks: 19.7 Me, 32.1 CH2, 43.1 CH2, 46.6 CH2Te & 55.8 for CHTe ppm. Its 125 Te NMR shows a single peak at 1026 ppm that indicates it is stable in solution.

Molecular Structures ofcyclic tellurium(IV) diiodide
Single crystal x-ray data and structure refinement details formolecule are given in table 1-3. ORTEPobservation of their molecular structures is depicted in figure2. Its most important bond length and bond angles relevant to its geometry are shown in captions. The cyclic tellurium(IV) diiodide, crystallizes in a monoclinic crystal system with the P21/c space group. In crystal packing diagram each unit cell contain eight molecules. Each molecule are interconnected through C-H---I intermolecular hydrogen bonding and Te---I secondary bonding interactions. (Shown in figure 3)In this report we are able to observed better refinement data than the earlier reported value. However observed R value (3.68) is slightly higher than the previous reported value (3.37) [13].Asymmetric unit of this molecule consists of two formula units and therefore, there are two crystallographically unique (but chemically similar). The geometry around the tellurium atom in themoleculesistrigonalbipyramidal. In whicha lone pair and two carbon atoms are located at equatorial positionand the iodine atoms are situated at the axial site. The five-membered rings acquire twist-boat shape structure. It should be well-known that the C-Te-C bond angles are 85.0(1)°& 85.

Chemicals and experimental methodology employed
All experimentwas carried out using syringe septa techniques underinert (N2 gas) atmosphere. Acetone, chloroform and other solvents employed in this experiment were freshly distilled and used. 1,3dibromopropane, and tellurium powder was purchased from Sigma Aldrich and used as received. Elemental analysis of the tellurium molecule was carried out on Perkin-Elmer 2400 elementalinstrument. Proton and 13 Carbon NMR spectra were recorded on Bruker 400 MHz apparatus at ambient temperature and the chemical shifts were measured in ppm relative to Me4Si for proton and 13 Carbon NMR. The 125 Tellurium NMR spectrum was recorded on Bruker 400 Megahertzinstruments. In this experiment dimethyl telluride (Me2Te) was employed as reference.

Synthesis of cyclic tellurium(IV)diiodide.
A solution of 1,4-dibromopentane, (1.36 ml, 10.0 mmol) in freshly distilled dry acetone (3 ml) was stirred at room temperature with a two-fold excess of NaI for 1 h. After 1 h, tellurium powder (1.27 g, 10 mmol) was added to the reaction mixture in two portions over a period of 30 minute at room temperature. After 24 h stirring, the reaction mixture was turned to a dark red colour solid. The product was dissolved in150 ml chloroform and filtered. The filtrate was evaporated under vacuum to give a red colour crystalline solid of 14, which was recrystallized from chloroform. Yield: 1.73 g (38 %), mp 112 R C (lit 110-112 R C) [11]. Anal.

Conclusion
In conclusion we have reported synthesis and single crystal x-ray studies of cyclic tellurium(IV) diiodide, 2-Methyl-1,1-diiodo-1-telluracyclopentane in good yield at room temperature. We hope the developed methodology can be employed for synthesis of a series of chalcogenatedheterocyclic derivatives. Our new single crystal x-ray studiesprovide monoclinic crystal system, space group P21/c with cell dimensions a = 9.9539 (4)