Nigel S. Dance

Solution studies of triorganotelluronium salts

Abstract Evidence for telluronium ylid formation via the salt method is obtained for Ph 2 Te(CH 2 COPh)Br, but generally telluronium salts (aryl) 2 Te(CH 2 R)X rapidly dissociate in chloroform solution to (aryl) 2 Te and RCH 2 X. The relative rates of dissociation of Ph 2 (CH 3 )TeX in CHCl 3 are: X = I > Br ∼ NCS > Cl > PhCOO. Conductivity and 1 H NMR data suggest the salts Ph 2 (CH 3 )TeX to be covalent and at least dimeric in CHCl 3 , but more ionic in DMSO and, to a lesser extent, a DMF. IR data indicate association in solid Ph 2 (CH 3 )Tel. Kinetic data show that the reaction of CH 3 I with excess Ph 2 Te (solvent) affords an equilibrium mixture of ionic and covalent forms of Ph 2 (CH 3 )Tel, the ionic species being formed via the covalent one. Spin trapping experiments with phenyl(t-butyl)nitrone indicate that oxidative addition of alkyl halides to Ph 2 Te and redcutive elimination of CH 3 SCN from Ph 2 (CH 3 )Te(NCS) proceed via radical pathways. A mechanism is proposed for oxidative addition which involves the preformation of a charge transfer complex of RX (alkyl halide) and diphenyltelluride.

Organotellurium carboxylates and related compounds: Structural and synthetic considerations

Summary The structures of Ph 2 Te(OOOCH 3 ) 2 , Ph 2 Te(OOOPh) 2 and ( p -EtOC 6 H 4 ) 2 -Te(OOCCH 3 ) 2 are considered to be based on a four-coordinate ψ-trigonal bipyramidal arrangement of groups about the central tellurium atom. There is evidence for non-equivalence of carboxylate groups in both the solid state and in solution for Ph 2 Te-(OOOPh) 2 and for ( p -EtOC 6 H 4 ) 2 Te(OOCCH 3 ) 2 . The carboxylate groups are as “ester”-like as in related organotin compounds. Attempts to isolate organotellurium triacetates from solution gave only mixtures of hydrolysis products. The spectrum of Ph 2 Te(NO 3 ) 2 is less readily interpreted but the balance of evidence favours a monomeric structure with unidentate or very unsymmetrically bidentate nitrate groups.

Aspects of the Chemistry of Diarylditellurides and Related Compounds containing Telurium to Tin Bonds

The examination mixtures of two ditellurides by mass and 1H nmr spectroscopies provides the first evidence for the existence of unsymmetrical diarylditellurides, RTeTeR′. Possible mechanisms for the redistribution reaction are discussed and it is noted that no positive support for a radical mechanism is obtained. Appearance potential measurements on the ion (aryl)Te+ derived from a number of organotellurium compounds suggest that tellurium extrusion may be a low energy pathway for the decomposition of diarylditellurides. A new series of compounds, Ph3SnTe(aryl) is reported and they are examined by 119Sn and 125Te Mosabauer spectroscopies. Attempts are made to interpret the Mosabauer data in terms of orbital populations, and it is demonstrated that only an sp bonding model gives a self-consistent interpretation of the combined tin and tellurium Mosabauer data.

Organotellurium derivatives of dicarboxylic acids

Abstract The freshly prepared sodium salts of ortho-phthalic acid and tetrabromo ortho-phthalic acid react with diaryltellurium dichlorides in chloroform to afford new dimeric organotellurium carboxylates, R 2 Te(C 8 X 4 O 4 ) 2 (X = H, Br). The new compounds contain fourteen membered rings and the detailed structure is discussed particularly in the light of the 1 H NMR spectrum of ( p -EtOC 6 H 4 ) 2 Te(C 8 H 4 O 4 ) 2 which shows inequivalence of p -ethoxy groups. The sebacate derivatives of tellurium(IV) are oligomeric and iso- and terephthalic acids failed to give well defined products.

Use of the metal-isotope technique (tin-116 and -124) to confirm assignments in the vibrational spectra of phenyltin compounds

Samples of isotopically pure (116Sn and 124Sn) tetraphenyltin, triphenyltin iodide, and triphenyltin acetate have been prepared and their i.r. spectra recorded. Shifts of bands corresponding to metal-sensrtive vibrations of the order of 5 cm–1 have been observed. In this way the results of earlier empirical studies are shown to be broadly correct but some assignments need modification. It is noted that the term ‘tin–phenyl stretch’ has physical significance.

Isotopic studies by vibrational spectroscopy of the tellurium–carbon bond in diaryltellurium dihalides

Isotopically pure (126Te and 130Te) samples of Ph2TeCl2, Ph2TeBr2, and (p-MeC6H4)2TeBr2 have been prepared. Examination of the low-frequency i.r. spectra (with confirmation from Raman spectra) enables definitive assignments of tellurium–carbon stretching vibrations to be made and also establishes this description of these vibrational modes to be physically realistic. The symmetric (Te–Cl) and Te–C) stretching vibrations of Ph2TeCl2 are coupled but ν(Te–Br) in Ph2TeBr2 is a relatively pure vibration.