Te-C bond

The following scheme depicts the preparation of the title compounds. 

2-ditellurolo)naphtacenef Tellurium powder (7.65 g, 60 mmol), 1.38 g (60 mmol) of sodium and 100 mL of dry dimethylformamide are placed in an argon-flushed flask fitted with a magnetic stirrer. The mixture is stirred and heated at 100°C for 1 h and then cooled to 55°C whereupon 5.0 g (14 mmol) of 5,6,11,12-tetrachlorononaphthacene followed by 100 mL of dimethylformamide are added. The resultant mixture is heated at 50°C for 20 h, poured into brine and filtered. The solid is dried, extracted with acetone and benzene and the solid is recrystallized from chlorobenzene. Yield 1.28 g (13%) m.p. 360°C. 

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Synthetic routes to macrocyclic ligands containing tellurium are still very limited, mainly because of the difficulties in sequentially introducing the necessary Te centres into organic fragments, the weakness of the Te C bonds and the unavailability or instability of many Te-containing analogues of the precursors for thio- and seleno-ether macrocycles. 

There are a number of examples known from weak-halogen bridges between T-shaped Y-Te-X complexes, like tuTe(Ph)Cl [Figure 30(a)] related weak cation-anion interaction occurs in the 2 1 complex [tu2Te(Ph)]+ Cl- [Figure 30(b)], The weak contact is generally the one trans to the Te-C bond ( trans effect of the strong Te-C bond).84,85... 

The Pauling electronegativities of carbon and tellurium are, respectively, 2.5 and 2.1. This, in addition to the large volume of the tellurium atom (atomic radius 1.37, ionic radius 2.21), promotes easy polarization of Te-C bonds. The ionic character of the bonds increases in the order C(sp ) Te>C(sp ) Te>C(sp)-Te, in accordance with the electronegativity of carbon accompanying the s character (Table 1.1). 

The Te-C bond therefore exhibits a high reactivity, as demonstrated typically by the easy heterolytic cleavage towards nucleophihc reagents. 

By treatment of the dichloroteUurolactone with excess NaBH4, the fission of the Te-C bond takes place with recovery of the starting y 5-unsaturated carboxylic acid. ... 

The low energy and high polarity of the Te-C bond allows the reactions to be performed starting from the telluroninm salts, instead of the ylides, nnder nentral conditions (method... 

There are a total of nine structures containing two Te—C bonds and seven different motifs can be discerned for these. The structures of Me2Te(S2COMe)2 (270) and Me2Te(S2COEt)2 (271) are isomorphous and the former is represented in Fig. 168. The xanthate ligands coordinate in an asymmetric fashion forming Te—SShort bond distances of 2.566(1) and 2.680(1) A [2.590(2) and 2.677(2) A... 

The X-ray structure of a tritellurole, cz s-3,5-dibenzylidene-l,2,4-tritellurole (13), has been reported (81TL4199). The tritellurole was shown to have a non-planar heterocyclic system in which the ditelluride bond forms a dihedral angle of 35.9° with the other three ring atoms. The Te—C bond lengths averaged 2.125 and the Te—Te bond length was shown to be 2.710 A. 

Examples of such carbon-containing tellurium compounds without a Te—C bond are ... 

When diethyl tellurium was heated with triethylsilane at 200° for seven hours, or with triethylgermane at 140° for seven hours, the Te — C bond was cleaved, ethane liberated, and mixtures of ethyl triethylsilyl tellurium/bis[triethylsilyl] tellurium or ethyl triethylgermyl telluriumlbis[triethylgermyl] tellurium were formed6. However, triethylstannane and diethyl tellurium yieled only bis[triethylstannyl] tellurium even at 20° 5 6. 

K.J. lrgolic Organic Tellurium Compounds with one Te,C Bond... 

Organic tellurium compounds with one Te—C bond containing divalent, tetravalent, or hexavalent tellurium have been prepared. The most widely investigated and best characterized compounds are the diorgano ditellurium derivatives and the organo tellurium trihalides. Pentafluoroethyl tellurium chloride tetrafluoride is the only known example of a hexavalent tellurium compound with one Te-C bond in the molecule. 

The following types of tellurium compounds with one Te-C bond in the molecule are known ... 

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