Furan derivatives of tellurium: Synthesis and structural comparison with the thiophene analogues

α-Bromo-2-acetylfuran adds oxidatively to elemental tellurium and aryltellurium(II) bromide at ambient temperature to afford (2-furoylmethyl)tellurium(IV) dibromides, (FuCOCH₂)₂TeBr₂ (1b) and Ar(FuCOCH₂)TeBr₂ (Fu = 2-C₄H₃O; Ar = 1-C₁₀H₇, 2b; 2,4,6-Me₃C₆H₂, 3b). The iodo analogues 1c-3c can be obtained by metathesis of the bromides with an alkali iodide. Condensation reactions of the parent methyl ketone with Te(IV) chlorides results in the corresponding chloro analogues, (FuCOCH₂)₂TeCl₂ (1a) and Ar(FuCOCH₂)TeCl₂ (2a, 3a and Ar = 4-MeOC₆H₄ (4a)). These diorganotellurium dihalides are reduced with aqueous bisulfite to diorganotellurides 1-3, which can be oxidized readily with dihalogens to the desired diorganotellurium(IV) dihalides. The tellurated furan derivative, bis(2-furyl)tellurium(II), Fu₂Te (5), obtained by detelluration of bis(2-furyl)ditelluride with electrolytic copper, gives crystalline bis(2-furyl)tellurium(IV) dichloride (5a) upon chlorination. Crystal structures of Te(IV) compounds 1a, 1b, 2a-4a, and the telluride 3 together with its thiophene analogue (2,4,6-Me₃C₆H₂)((2-C₄H₃S)COCH₂)Te, 6 have been studied. Among the Te(IV) compounds, the functionalized organic moiety, FuCOCH₂-, behaves as a (C, O) chelating ligand, resulting in a intramolecular 1,4-Te?O secondary bonding interaction. Such an interaction is absent in Te(II) compounds 3 and 6, though they differ in the conformation adopted by the organic ligand. The chalcogen atoms in the heteroaroyl moiety are trans in 3 but cis in 6 which also possesses intermolecular Te?O interaction in its lattice.