Organotellurium chemistry

Organotellurium chemistry in chemistry describes the synthesis and properties of chemical compounds containing a carbon to tellurium chemical bond.[1] Organotellurium chemistry was developed in the wake of organoselenium chemistry and, though sharing the same group in the periodic table, their chemistries are very different given the inversion of polarity in the chalcogen-carbon bond.[2]

Functional groups

General structures of some organotellurium compounds

The Te analogues of common organosulfur functional groups are known. Tellurols are unstable. Diorganomono- and ditellurides are the most commonly encountered organotellurium compounds. Telluroxides (R₂TeO) are also known.

Synthesis

Commonly used tellurium based reagents are hydrogen telluride, NaHTe, sodium telluride, and PhTeLi. Because Te is insoluble and polymeric, it is often not a useful precursor to organotellurium compounds, but it is attacked by hydride reducing agents:

Te + 2LiBHEt₃ → Li₂Te + H₂ + 2 BEt3

and organolithium compounds:

Te + RLi → RTeLi

One departure from sulfur and selenium chemistry is the availability of the tetrachloride TeCl₄.[3] Tellurium tetrachloride reacts with alkenes and alkynes to the chloro tellurium trichloride addition product:

RCH=CH₂ + TeCl₄ → RCH(Cl)-CH₂TeCl₃

These organotellurium derivatives are susceptible to further reactions.

Applications

Organotellurium compounds have few applications. Dimethyl telluride is used to in the metalorganic vapour phase epitaxy where it serves as a volatile source of Te. It is the only organotellurium compound that has been quantified in environmental samples.[4]

Organic synthesis

Diphenyl ditelluride is used as a source of PhTe⁻ in organic synthesis. Some of its reactions are:

• Organic reduction of aldehydes, alkenes, alkynes, nitro compounds, oxiranes to alkenes
• Debromination of vicinal dibromides with E2 elimination

Other methods in organotellurium chemistry include:

• Tellurium in vinylic tellurium trichlorides can be replaced by halides with a variety of reagents (iodine, NBS)
• Detellurative cross-coupling reaction: Compounds of the type Ar₂TeCl₂ engage in a coupling reaction to the corresponding biaryls with Raney nickel or palladium[5]

Another type is this Stille reaction:[6]

• Hydrotelluration: Compounds of the type RTeH react with alkynes R'CCH to R'HCCTeR with anti addition to a Z-alkene. In contrast hydrostannylation, hydrozirconation and hydroalumination in similar reactions react with syn addition.
• Te/Li exchange in transmetallation[7] is used in the synthesis of lithium reagents with demanding functional groups.
• Allylic oxidation: like the selenium counterpart selenoxide oxidation, allylic telluroxides undergo [2,3]-sigmatropic rearrangements forming allylic alcohols after hydrolysis.
• Olefin synthesis: Like the selenium counterpart selenoxide elimination, certain telluroxides (RTeOR) can form alkenes on heating.

References

1. Nicola Petragnani, Tellurium in Organic Synthesiss 1994, Academic Press, New York. ISBN 0-12-552810-8
2. M. Detty, M. O'Regan, Tellurium-Containing Heterocycles., John Wiley & Sons, Inc., New York, 1994 ISBN 0-471-63395-X
3. Lars Engman, "Tellurium(IV) Chloride" E-EROS. 2001. doi:10.1002/047084289X.rt003
4. Wallschläger, D.; Feldmann, F. (2010). Formation, Occurrence, Significance, and Analysis of Organoselenium and Organotellurium Compounds in the Environment. Metal Ions in Life Sciences. 7, Organometallics in Environment and Toxicology. RSC Publishing. pp. 319–364. ISBN 978-1-84755-177-1.
5. For an example see: Organic Syntheses, Coll. Vol. 6, p.468 (1988); Vol. 57, p.18 (1977). http://orgsynth.org/orgsyn/pdfs/CV6P0468.pdf
6. Palladium- and copper-catalyzed cross-coupling and carbonylative cross-coupling of organotellurium compounds with organostannanes (Chem. Commun. 1999, 2117) - Royal Society of Chemistry Suk-Ku Kang, Sang-Woo Lee and Hyung-Chul Ryu Link
7. For an example see: Organic Syntheses, Coll. Vol. 9, p.234 (1998); Vol. 72, p.154 (1995). http://orgsynth.org/orgsyn/pdfs/CV9P0234.pdf