Stereospecific chlorotelluration of terminal acetylenes

Chlorotelluration of terminal acetylenes, RCHtriple bond; length of mdashCH (R = Ph, 1; 4-MeC6H4, 2; t-Bu, 3) with aryltellurium trichlorides and TeCl4 in refluxing toluene affords (2-chloro-2-organylvinyl)tellurium(IV) dichlorides, Ar[R(Cl)Cdouble bond; length as m-dashCH]TeCl2 (Ar = 1-C10H7, 1Aa–3Aa; 2,4,6-Me3C6H2, 1Ba–3Ba; 4-MeOC6H4, 1Ca) and [t-Bu(Cl)Cdouble bond; length as m-dashCH]2TeCl2, 3a respectively. These Te(IV) derivatives on reduction with Na2S2O5 give the corresponding vinyltellurides as oils, except (2,4,6-Me3C6H2)[Ph(Cl)Cdouble bond; length as m-dashCH]Te (1B) which is a crystalline solid. The dibromides (1Ab–3Ab, 1Bb–3Bb, 3b) and diiodides (1Ac–3Ac, 1Bc–3Bc, 1Cc) were obtained by the oxidative addition of dihalogens to the tellurides. The stereochemistry of the products has been established with the help of X-ray diffraction studies of 1Aa, 1Ba, 1Bc, 1Cc, 3Aa, 3a and 1B. Intramolecular Te⋯Cl attractive interactions appear to favor the (Z) conformation adopted by the 2-chloro-2-organylvinyltellurium group irrespective of the steric demand of the aryl ligand of the Te(IV) electrophile and the terminal acetylene substituent. The intermolecular Te⋯X secondary bonding interactions give rise to dimeric units in the lattices of 1-naphthyl- and anisyltellurium(IV) derivatives, but are absent among the mesityl analogues, consistent with the larger steric requirement of the latter ligand.