Organotellurium halides

Organotellurium halide Organotellurium oxide Organotellurinic acid anhydride... 

Organic tellurium halides 7 are normally unstable and cannot be isolated. Attempts to isolate organotellurium halides lead to their disproportionation, giving a mixture of organotellurium trihalides 5 and the corresponding diorganoditellurides 4 (Equation (1)). In this way, they are generated and used in situ.5 11 12... 

An electron-donating group suitably positioned, able to coordinate with tellurium, stabilizes organotellurium halides, allowing their isolation (Figure 4) 5 11 12 16 Recently, compound 11 was isolated by careful crystallization.17... 

Figure 4 Intramolecular coordination with tellurium lead to stable organotellurium halides.

This class of electrophilic organotellurium compounds is prepared by the controlled addition of a halogen to diorganoditellurides. For many years, naphthyltellurium iodide, prepared for the first time in 1959,78 was the only stable organotellurium halide known in the solid state. Those containing an ortho-group able to coordinate with tellurium can be isolated (Scheme 10).S 10,11 79... 

When such groups are not present, the organotellurium halide cannot be isolated. In these cases, aryl, alkenyl, and alkyl tellurenyl halides, usually bromides and iodides, are prepared and used in situ. ... 

The discovery by Petragnani80 that organotellurium halides can be generated and captured in situ by nucleophiles opened a new chapter in organic tellurium chemistry, as exemplified by the reactions described in Section 9.13.6.1. 

This class of organotellurium compounds is an important source of nucleophilic (Sections 9.13.3.1 and 9.13.3.2) or electrophilic (Sections 9.13.4.2.4 and 9.13.4.3) tellurium species. Diorganoditellurides can also behave as electrophiles, but in such cases normally one organotellurium group is lost. In this way, the corresponding organotellurium halides (Section 9.13.4.3) are prepared as source of electrophilic tellurium. In the past, the title compounds were prepared mainly by reduction of aryltellurium trihalides, in some cases under drastic reaction conditions5 9 11 12 (Scheme 11). 

In this section, the reactions of electrophilic tellurium species will be considered. Among these species are tellurium tetrachloride 16, organotellurium halides 7, organotellurium trihalides 5, and also diorganoditellurides 4, since these species can be attacked by carbanions. Diorganotellurium oxides 8, arenetellurinic acid anhydrides 9, and other oxidizing agents will also be discussed in Section 9.13.6.3, since in these species the tellurium atom is electron deficient. 

The most synthetically useful reaction of nucleophilic tellurium consists in the reaction of organotellurium halides with organometallics. This reaction was systematically studied for the first time by Petragnani several years ago.80 In recent years, it has been used to prepare a number of tellurium-containing organic substrates. The general route is shown in Scheme 57. 

Vinylic tellurides bearing simple vinyl groups (e.g., CH2=CH, PhCH=CH) can be prepared by reacting the corresponding lithium or Grignard reagents with organotellurium halides.8 ... 

If unusual vinylic tellurides or vinylic tellurides of defined stereochemistry are required, other vinyl organo-metallics are employed. In recent years, a number of methods of preparing vinylic derivatives of tellurium using organotellurium halides have been developed. 

When telluroalkynes 105 are submitted to the hydrozirconation, only the vinylzirconium intermediates 106 are formed.179,181 These are captured with organotellurium halides to give bistelluroketene acetals 107 (Scheme 64).179... 

Several structurally characterized organotellurium halides have been found to be associated in the solid state. For example, a-dimethyltellurium dichloride, Me2TeCl2, forms a polymeric array (Te-Cl 2.541 and 2.480 A Te- Cl 3.46 and 3.52 A) [482]. -Me2Tel2 is a self-organized polymer (Te-12.854-2.994 A, Te- -13.659-4.030 A) [483] whereas j5-Me2Tel2 is a ionic compound [Me3Te]+[MeTel4] with cation-anion secondary bond interactions (Te- - -I 3.84-3.400 A) [484]. 

Organotellurium(II) compounds can also contain a three-center, four-electron bond as shown for 39 to 42 in Fig. 19. Typically, these molecules contain an odd number ligands around the central atom and an electronegative atom helps to stabilize a tellurenyl halide or selenenyl halide bond through chelation to form a four, five, or six membered ring. " Such molecules are described as lO-Te-3 and lO-Se-3... 

Organotellurium tri- and dihaUdes undergo a-elimination by oxidative, photolytic or thermal routes, giving the corresponding halides with a selective transference of the halogen at the position where the tellurium moiety was originally attached (/pxo-substitution). 

Organic halides from organotellurium(IV) halides (typical procedures). Method To 1-chlorocyclohexyltellurium trichloride (0.35 g, 1.0 mmol) in dioxane (5 mL) is added f-BuOOH (70%, 0.26 g, 2.0 mmol) and the mixture stirred under reflux for 30 min, during which period a pale yellow solid precipitates. After cooling at room temperature, the precipitate is filtered off, and the filtrate poured into brine and then extracted with ether (3x30 mL). The ether extract is dried (MgS04), and GLC analysis reveals the presence of 1,2-dichlorocyclohexane (0.14 g (92%), cisitrans = 7 93) (using phenyl acetate as the internal standard). 

In 1996, Detty and coworkers reported on the oxidation of sodium halides to positive halogens with hydrogen peroxide in two-phase systems of dichloromethane and pH 6 phosphate buffer, catalyzed by organotellurium catalysts 237 (Scheme 181)545. Mixtures of 1,2-dihalocyclohexane (238) and 2-halocyclohexanol (239) were formed upon reaction of the positive halogens formed with cyclohexene. From the three tellurium catalysts... 

Xenon halides reactions with organic radicals 5.9 organoboranes 5.9 organotelluriums 5.9... 

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