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.

Hitherto unknown 2-furoylmethyl and 2-furyl derivatives of tellurium have been prepared and studied structurally vis-à-vis the thiophene analogues. The planar heteroaroyl fragments 2-C4H3EC(O)- (E = O, S) differ in their modes of bonding and conformations. In Te(II) compounds, the chalcogen atoms are trans in 2-furoyl but cis in 2-thiophenoyl moiety.Figure optionsDownload as PowerPoint slideHighlights
► 1H, 13C, 125Te NMR data of 2-furoylmethyl and 2-furyl compounds of Te are reported.
► Structures of 2-furoylmethyltelluriums studied vis-à-vis their thiophene analogues.
► 2-Furoylmethyl moiety in Te(IV) compounds, behaves as a (C, O) chelating ligand.
► The hetero atoms are trans in 2-furoyl but cis in 2-thiophenoyl in Te(II) compounds.