Some Aspects of Organotellurium Chemistry

Abstract

A series of novel organotellurium dicarboxylates has been prepared by the reaction of diaryltellurium dichlorides with the di-sodium salts of o-phthalic acids. These compounds are dimeric, and spectroscopic evidence indicates that the carboxylate groups are unidentate. Monomeric species, involving axial (’long’) and equatorial ('short') Te-C bonds were not obtained. The salt method, often used for the preparation of sulphonium ylids has been used in the attempted preparation of telluronium ylids from suitable telluronium salts. In the case of diphenylbenzyltelluronium bromide cleavage of the Te-CH2Ph bond took place in organic solvents. Diarylphonacyltelluronium salts were found to give telluronium ylids, but these were not isolable, because of the ease of cleavage of the Te-aliphatic bond. The behaviour of various diorgano-methyltelluronium salts in organic solvents has been investigated, and evidence obtained for the existence of two species in solution, represented as R2MeTe+X- and R2MeTe-X; the decomposition of these telluronium salts is rationalised in terms of the existence of two species. The vibrational spectra of various organotellurium and organotin compounds have been assigned following the application of isotopic substitution techniques; the assignments are thus placed on an experimental basis, whereas previous assignments have been essentially empirical. The results, which are in general agreement with previous assignments, indicate the validity of considering specific modes as representing Sn-Ph or Te-Ph stretching vibrations; these modes are also described as phenyl(t) modes, using the Whiffen notation. Application of isotopic substitution has also aided the assignment of Te-Me stretching modes in ∝-ME2TEI2 and Ph2MeTe+I-.125Te Mossbauer parameters are presented for a number of organotellurium compounds, and the results are discussed in terms of 5s and 5p electron distributions around the tellurium atom. Both 125Te and 119Sn Mossbauer parameters have been determined for compounds of the type Ph3Sn-Te-R, and the results are combined to give a more complete description of the electron distribution within these compounds. Mass spectrometric and other spectroscopic data has proved the existence of unsymmetrical diarylditellurides, R-Te-Te-R', in equilibrium with the two symmetrical compounds R2Te2 and R'2Te2. Measurements of Mass spectrometric appearance potentials for various organotellurium compounds have enabled comparison to be made of bond strengths in various organotellurium compounds.