The chemistry of some organotellurium compounds

Abstract

Tbe formation of Pd(TeR)_n and (CuTeR)_n from the reaction
between telluroesters and Pd(II)or Cu(II) suggested that these organa­tellurium reagents may be useful precursors of RTe^- ligands in reactions with transition-metal substrates.
Also the formation of telluronium salts Me₂RTeI^- from the reaction between telluroesters and methyl iodide, together with the above, confirm the cleavage of -c_õ-Te bonds rather than -C-Te bonds.
The formation of a carboxylic acid from the toluene solution of a ditelluride d palladium(O) complex in the presence of light oxygen (from air) is demonstrated. When the solvent employed is p-xylene an aldehyde is formed.The reaction proceeds via the free radical, RTeO, with Pd(PPh₃)₄ as a catalyst.It has also been shown that the oxidation of aldehydes to carboxylic acids is catalysed by ditelluride.
Spin trapping experiments with PhCH=N(O)Bu^t (phenyl-t-butyl-nitrone) have provided evidence that the oxidative addition of an alkyl halide (RX=Mei, BuⁿBr, Bu^secBr, Bu^tBr, BrCH₂-CH=CHCH₂Br, and Br(CH₂)₄Br) to diphenyltelluride and reductive elimination of CH₃SCN from Ph₂(CH₃)Te(NCS) proceeds via radical pathways. A mechanism is proposed for oxidative addition which involves the preformation of a charge transfer complex of alkyl halide and diphenyltelluride.The first step is the formation of a charge transfer complex, and the initial product of the oxidative addition is a "covalent" form of the tellurium(IV)compound. When the radical R is more stable, Ph₂TeX₂ may be the major tellurium(IV)product.
The reaction of RTeNa (R=p-EtOC₆H₄, Ph) with organic dihalides X₂(CH₂)_n (n=1,2,3,4) affords telluronium salts (n=3,4; X=Cl, Br) the nature of which is discussed.For n=l (X=Br, I)the products are formulated as charge transfer complexes of stoichiometry (RTe)₂(CH₂).CH₂X₂• For n=2, elimination of ditelluride occurs with the formation of an alkene.
Some ^125’Te Mõssbauer data are discussed and it is suggested that the unusually low value of 6 (7.58 mm.s-1 ) for  p-EtO.C6H4.Te)2(cH2)cH2Br2 relates to removal of 5's electronsfrom the spare pair orbltal via the charge transfer interaction. ¹²⁵Te Mossbauer data for (p-EtO.C₆H₄)Te(CH₂)₄Br are typical of a tellurium (IV) compound and in particular ∇ is in the expected range for a telluronium salt. The product of the reaction of Na Te (C₆H₄.OEt), with 1,3-dibromopropane is, from the Mössbauer data, also a telluronium salt.

Date of Award	1982
Original language	English
Supervisor	William R. McWhinnie (Supervisor)