α-Telluration of 2,4,6-trimethylacetophenone under mild conditions: Role of steric factor in the solid state structures of Te(II and IV) compounds

Elemental tellurium inserts into the Csp3–Br bond of α-bromomesitylmethyl ketone and due to its strong carbophilic character affords the crystalline C-tellurated derivative of 2,4,6-trimethylacetophenone, (MesCOCH2)2TeBr2, 1b in over 80% yield. Electrophilic substitution of the parent ketone with aryltellurium trichlorides, at room temperature, gives nearly quantitative yields of unsymmetrical alkylaryltellurium dichlorides (MesCOCH2)ArTeCl2 (Ar=mesityl, Mes, 2a; 1-naphthyl, Np, 3a; anisyl, Ans, 4a). Fairly stable mesitoylmethyltellurium(II) derivatives, (MesCOCH2)2Te, 1 and (MesCOCH2)ArTe (Ar=Mes, 2; Np, 3 and Ans, 4) obtained as the reduction products of their dihalotellurium(IV) analogues, readily undergo oxidative addition of dihalogens to afford the corresponding (MesCOCH2)2TeX2 (X=Cl, 1a; Br 1b; I, 1c) and (MesCOCH2)ArTeX2 (X=Cl, Br, I, Ar=Mes, 2a, 2b, 2c; Np, 3a, 3b, 3c and Ans, 4a, 4b, 4c). Crystallographic structural characterization of 1, 1b, 2, 2a, 2b, 2c, 3, 3a and 4c illustrates that the steric demand of mesityl group appreciably influences primary geometry around the 5-coordinate Te(IV) atom when it is bound directly to it. It also makes the Te atom inaccessible for the ubiquitous Te⋯X intermolecular secondary bonding interactions that result in supramolecular structures. In the crystal lattice of symmetrical telluroether 1, an interesting supramolecular synthon based upon reciprocatory weak C–H⋯O H-bonding interaction gives rise to chains via self-assembly.