2-Thiophenyltellurium derivatives: Alternative synthetic routes and structural characterization

Grignard reagent prepared from 2-thiophenyl bromide in THF consumes elemental tellurium readily at room temperature and provides a route to obtain bis(2-thiophenyl)ditelluride, Tpn2Te2 (1, Tpn = 2-C4H3S) in good yield. It can also thiophenylate aryltellurium(II) bromides, producing solutions of mixed aryl(heteroaryl)tellurides, which when chlorinated give crystalline aryl(heteroaryl)tellurium(IV) dichlorides, ArTpnTeCl2 (Ar = 1-C10H7, Npl; 2,4,6-Me3C6H2, Mes). Oxidative addition of α-bromo-N,N-diethylacetamide to (2-thiophenyl)tellurium(II) bromide, gave the mixed alkyl(heteroaryl)tellurium(IV) dibromide, (Et2NCOCH2)TpnTeBr2. Ditelluride 1 can be detellurated by electrolytic copper to the bis(2-thiophenyl)telluride, Tpn2Te (2). Chemical shifts, δ(1H, 13C and 125Te) for (2-thiophenyl)tellurium(IV) halides are reported. Crystal structures of Tpn2TeBr2 (2b), Tpn2TeI2 (2c) and Mes(Tpn)TeCl2 (2e) have been determined unambiguously. In the case of 2e, steric repulsion of the mesityl ligand counters the tellurium lone pair repulsion to widen the equatorial C–Te–C angle to the extent of 108°. In the crystal lattices of 2b and 2c, the intermolecular Te⋯X secondary bonds give rise to an interesting tetrameric supramolecular architecture with S2 symmetry that defies the stereochemical activity of the lone pair on the central tellurium atom.