Dibenzotellurophenes

Dibenzotellurophene, [RhCp Cl2]2, and silver inflate yield the ri (Te) coordinated product 329 [97JCS(D) 1579]. In the absence of silver triflate, species 330 is formed. Reduction of 329 with dicyclopentadienyl cobalt results in 331. If, however, this process is conducted in the presence of Fe3(CO)i2, ring-opened products 332 and 333 are isolated. 

Dibenzotellurophene Tellurium powder (6 g, 47 mmol) and dibenzothiophene S.S -diox-ide (8 g, 37 mmol) are mixed thoroughly, the mixture is carefully heated under an atmosphere of carbon dioxide until evolution of sulphur dioxide commences, and the temperature is then regulated to achieve a steady evolution of sulphur dioxide. From time to time the sublimed dibenzothiophene dioxide is melted and allowed to flow back into the reaction mixture. After 36 h, the mixture is cooled to 20°C and extracted with boiling acetone. The extract is evaporated to dryness, the solid residue is washed several times with cold ethanol, and the washings are collected and evaporated. The residue is steam distilled and the product is recrystallized from light petroleum ether. Yield 1.0 g (10%) m.p. 93°C. 

Dimethyldibenzotellurophene. Powder tellurium (0.94 g 7.4 mmol) is thoroughly mixed with 2.61 g (6.1 mmol) of pure 4,4-dimethyl-2,2 -biphenyldiyl mercury, the mixture is placed into a sublimation apparatus equipped with a cold finger, and slowly heated under vacuum in a metal bath to 260-270°C. Colourless needles begin to sublime at 228°C. The temperature is held at 260°C for 12 h. The sublimate is recrystallized from a mixture of 300 mL of methanol and 10 mL of carbon tetrachloride. Yield 1.38 g (79%) m.p. 158°C. Dibenzotellurophene was similarly obtained in 82% yield. 

The reaction of TeCl4 with two or more molar equivalents of 2,2 -dilithiobiphenyl gives dibenzotellurophene and the formulated telluronium chloride as by-product. ... 

The nature of the complexes of tellurophene and its benzo analogs depends on the type of metal carbonyl. Thus, interaction of tellurophene with (MeCN)3Cr(CO)3 yields the -complex [2 E = Te M = Cr(CO)3], whereas the reaction with Fe3(CO)12 is a complicated transformation [96JCS(D) 1545]. A similar reaction is observed for dibenzotellurophene. 

More evidence for the increased steric strain caused by the voluminous ditelluride unit encased in a ring may be found in the reaction of the derivative of o.o -dithiodiphenyl 88 with chalcogens (84JHC413). Whereas the treatment of 88 with selenium allows the formation of the six-membered heterocycle 89 (although in a very low yield of 4%), the reaction with tellurium results in dibenzotellurophene 90 formed, most probably, through extrusion of tellurium from the cyclic ditelluride similar to 89. 

The tendency of intermediate heterocyclic ditellurides to eliminate one of the tellurium atoms thus contracting the size of the ring is illustrated by the course of the oxidative cyclization of the dilithio dichalcogenides 78 (84JHC413). Whereas in the case of the diselenolate 78 (M = Se) the expected heterocyclic diselenide 79a is formed, albeit in low yield, the analogous reaction with the ditellurolate 78 (M = Te) results in an extrusion of elemental tellurium affording dibenzotellurophene 79b. 

Treatment of 2,2 -diiodobiphenyl derivatives 74 with Te-Cu in NMP affords the dibenzotellurophenes derivatives 75 <95JOC5274>. The 2,2 -biphenylylenediphenyltellurane 76 was prepared and warmed to 140° until it decomposed to dibenzotellurophene in 69% yield. NMR studies confirmed the formation of 76 which was isolated as a pale yellow solid <95TL2803>. The synthesis and X-ray analysis of air sensitive 21-telluraporphyrin derivatives 77 was reported <95AG(E)2252>. 

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