Solution studies of triorganotelluronium salts

Evidence for telluronium ylid formation via the salt method is obtained for Ph₂Te(CH₂COPh)Br, but generally telluronium salts (aryl)₂Te(CH₂R)X rapidly dissociate in chloroform solution to (aryl)₂Te and RCH₂X. The relative rates of dissociation of Ph₂(CH₃)TeX in CHCl₃ are: X = I > Br ～ NCS > Cl > PhCOO. Conductivity and ¹H NMR data suggest the salts Ph₂(CH₃)TeX to be covalent and at least dimeric in CHCl₃, but more ionic in DMSO and, to a lesser extent, a DMF. IR data indicate association in solid Ph₂(CH₃)Tel. Kinetic data show that the reaction of CH₃I with excess Ph₂Te (solvent) affords an equilibrium mixture of ionic and covalent forms of Ph₂(CH₃)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 Ph₂Te and redcutive elimination of CH₃SCN from Ph₂ (CH₃)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.