Alkoxycarbonylmethyl derivatives of tellurium: Facile synthesis and structural studies

Methyl and t-butyl esters of α-bromoacetic acid added oxidatively to elemental tellurium in the presence of sodium iodide to give high yields of crystalline bis(alkoxycarbonylmethyl)tellurium(IV) diiodides, (ROCOCH2)2TeI2. The chloro and bromo analogs were prepared via their reduction into tellurides followed by dihalogen oxidation. Activation of the α-Csp3–Br bond by ester functionality appears to be insufficient as methyl α-bromoacetate failed to add to Te(0) or aryltellurium(II) bromides. The nucleophilic substitution reaction of α-bromoesters with aryltellurolates, ArTe−Na+ (Ar = 1-C10H7, Np; 2,4,6-Me3C6H2, Mes), gave (alkoxycarbonylmethyl)aryltellurides that were characterized as mixed diorganotellurium dihalides. Crystal structures of Np(MeOCOCH2)TeBr2, Mes(MeOCOCH2)TeBr2 and Mes(t-BuOCOCH2)TeCl2 show that the functionalized organic moiety, ROCOCH2, behaves as a (C, O) chelating ligand. The carbonyl O atom of the ester group in these compounds is involved in a 1,4-Te⋯O secondary bonding interaction. However, the functionalized ligands in the case of (MeOCOCH2)2TeI2 are devoid of such an interaction. Surprisingly, one of the two organic ligands in (MeOCOCH2)2TeBr2 takes part in an intramolecular 1,4-Te⋯O interaction, the other appears to involve an intermolecular Te⋯O interaction to result in a one-dimensional array of molecules in the crystal lattice.