Telluronium Salts Research Articles

Telluronium salt chemistry: Some fluorides and carboxylates

Ph 3TeF is ionic and no evidence is obtained for a covalent form in solvents of relatively low polarity. By contrast significant covalent interaction is seen for Ph 2(CH 3)Te(OOCR)(R=Ph, o-CH 3O·C 6H 4-, m-NO 2·C 6H 4). Factors influencing the formation and stability of covalent forms of telluronium “salts” are discussed. Phenyl(methyl)telluronium- ortho-phthalate is shown to be a monomer in chloroform solution. The structure of the compound is discussed in relation to NMR and IR data and against the background of previous literature reports of both dimeric and monomeric diorganotellurium- ortho-phthalates.

Solution studies of triorganotelluronium salts

Evidence for telluronium ylid formation via the salt method is obtained for Ph 2Te(CH 2COPh)Br, but generally telluronium salts (aryl) 2Te(CH 2R)X rapidly dissociate in chloroform solution to (aryl) 2Te and RCH 2X. The relative rates of dissociation of Ph 2(CH 3)TeX in CHCl 3 are: X = I > Br ∼ NCS > Cl > PhCOO. Conductivity and 1H 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 3I with excess Ph 2Te (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 2Te and redcutive elimination of CH 3SCN 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.

Studies of diorganotellurium diisothiocyanates and of a triorganotellurium isothiocyanate in the solid state and in solution

The synthesis of the first diorganotellurium dithiocyanates is reported. It is argued that the tellurium interacts more strongly with the nitrogen than with the sulphur atom of the NCS group. Two structural classes are noted: (a) R 2Te(NCS) 2 (R  Ph, p-CH 3O · C 6H 4) in which interaction of tellurium with the two NCS groups is equal and in which intermolecular association via long TeS bonds probably occurs; (b) [R 2Te(NCS)](NCS) (R  p-C 2H 5O · C 6H 4) in which the tellurium interacts unequally with the two NCS groups to give a structure with some “telluronium salt” character. The chemistry of MePh 2Te(NCS) is studied. In solvents of reasonable polarity (e.g. DMSO), and probably in the solid state, it behaves as an essentially ionic telluronium salt [MePh 2Te](NCS). However, in CDCl 3 solution it exists in a covalent form, MePh 2Te(NCS), from which reductive elimination of, exclusively, methyl thiocyanate occurs. The mechanism of the decomposition is not simple: initially it is probable that a free radical pathway dominates, but after approximately 100 min the rate of decomposition increases. There is evidence that the second rate process is catalysed by diphenyltelluride. Other salts, [MePh 2Te]X (X  BF 4, PF 6) are reported for comparison.

Chemistry

THE eleventh volume of Dr. Mellor's “Comprehensive Treatise” includes the element tellurium, held over from the previous volume on sulphur and selenium, and the half-brothers of the oxygen family, chromium, molybdenum, and tungsten, but without uranium. All these elements raise interesting problems of valency; but the section on the valency of tellurium is unfortunately already out of date, since the evidence cited on p. 32 for the coplanar configuration of the four radicals in the telluronium salts has been obsolete since the end of 1928, whilst positive evidence of the tetra-hedral configuration was provided at the end of 1929. The chromium ammines are catalogued with characteristic thoroughness under ninety subheadings, and stereo-isomerism is suggested as a possible explanation of the existence of multiple forms of certain members of the series, but the index contains no references by which general phenomena, such as co-ordination, isomerism, or stereo-isomerism, can be discovered. On the other hand, the interesting oxy-salts, which are so characteristic of this family of elements, can be traced quite readily by referring to entries under chromyl, molybdenyl, and uranyl compounds.

CCCLXXXIX.—Studies of valency. Part XIV. An optically active telluronium salt: phenyl-p-tolyl-methyltelluronium iodide

CCCLXXXIX.—Studies of valency. Part XIV. An optically active telluronium salt: phenyl-p-tolyl-methyltelluronium iodide