Organometallic tellurium

Organometallic Tellurium Reaction Conditions Product Yield m.p. Refer-... 

The research volume in organic and organometallic tellurium chemistry has grown very rapidly in recent years. 

The wide substrate tolerance of lipases is demonstrated by the resolution of organometallic substrates [129-131]. The presence of tin, selenium, or tellurium in the structure of secondary alcohols does not inhibit the lipase activity and enantiopure organometallic alcohols were obtained by acylation in organic media (Figure 6.48). 

The environmental impact of tin is appreciable, as it is one of the three most enriched metals—only lead and tellurium precede—in the atmospheric particular matter, as compared with the abundance of the element in the earth crust (2.2 ppm). Tin releases to the environment can be methylated by aquatic organisms, yielding organometallic species of toxicity comparable to that of methylated mercury5. 

It is now well established that organometallic compounds are formed in the environment from mercury, arsenic, selenium, tellurium and tin and hence were also deduced on the basis of analytical evidence for lead, germanium, antimony and thallium. Biological methylation of tin has been demonstrated by the use of experimental organisms. Methylgermanium and methyllead were widely found in the environment but it is debatable whether germanium and lead are directly methylated by biological activity in natural environment. 

Petragnani, N. Tellurium in Comprehensive Organometallic Chemistry II (ed. A. McKillop). Vol. 11, Chapter 14. Pergamon, Elsevier, 1995. 

The reaction of bis-phenylpropargyl ether (321) with tris(triphenylphosphine)rhodium chloride in benzene or toluene led to the formation of the unusual organometallic compound (322), which can be viewed as a derivative of an oxygen-rhodium pentalene system. Reaction of the rhodium complex (322) with sulfur leads to the corresponding 4,6-diphenyl-l,3-dihydro[3,4-c]furan (323). The selenium and tellurium analogs (324) and (325) were made in a similar manner (Scheme 111) (76LA1448). 

Since sulfur chemistry lies beyond the scope of this review and organo-tellurium chemistry so far has not been of any impact on organometallic chemistry in general, this section will be restricted to the discussion of redistribution equilibria on selenium. 

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. 

The introduction of tellurium into an organic substrate promotes functional groups transformations or presents structural features that can be used for synthetic purposes, if suitable methods to remove tellurium from the resulting structures are available. To date, four main strategies have been explored for this end, namely, the telluroxide elimination, the tellurium/metal exchange, the coupling of tellurides with organometallic species and with alkynes, and the reductive removal via free radicals. 

These tellurium-metal exchanges are also possible, but have received less attention due to the lesser utility of the resulting organometallics or to the less attractive reaction conditions when compared with tellurium-lithium... 

Since the publication of the chapter Tellurium in the second edition of this encyclopedia,12 a number of methods to transform organotellurium compounds into tellurium-free reactive organometallics and the use of such species in stereoselective carbon-carbon bond formation have been developed. Coupling reactions of organotellurium... 

Aryl tellurium trichlorides are easily converted to symmetrical or unsymmetrical diaryl tellurium dihalides via reactions with organometallic compounds (see p. 549). Trimethyl(aryl)silanes transfer only the aryl group to tellurium1. 

From Aryl Tellurium Halides 10.1. With Organometallic Compounds... 

Because a number of these organometallic compounds are commercially available, they are convenient starting materials for the preparation of certain aliphatic and aromatic diorgano tellurium dihalides. Tetraorgano tin and lead compounds transfer only two of their four organic groups to tellurium. Experiments with dialkyl-diaryl compounds showed that only the aryl groups are transferred. 

J. N.E. Day, A review of work on organic tellurium compounds and other organometallic compounds Univ. London, Science Progress 23, 211 (1928). 

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