Dicationic ditelluride salts stabilized by N-heterocyclic carbene

Abstract

Treatment of 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-tellone 1 with Tf₂O in CH₂Cl₂ resulted in the formation of dicationic ditelluride salt 2²⁺ 2 (OTf)⁻ as air-stable green crystals in 88% yield. The anion exchange reaction of 2²⁺ 2 (OTf)⁻ with Na[B(C₆F₅)₄] proceeded in CH₃CN at room temperature giving the corresponding borate salt 2²⁺ 2 [B(C₆F₅)₄]⁻ as blue crystals in 40% yield. The structures of these dicationic ditelluride derivatives were fully characterized on the basis of their NMR spectroscopic data and X-ray crystallography. In the crystalline state of 2²⁺ 2 (OTf)⁻, two NHC ligands are entirely perpendicular to the central Te–Te bond with a Te–Te–C–N torsion angle of 89.93(19)°. In sharp contrast, X-ray analysis of 2²⁺ 2 [B(C₆F₅)₄]⁻ revealed that two NHC ligands and the central Te–Te moiety are essentially coplanar with a Te–Te–C–N torsion angle of 7.99(17)°. In the DFT calculation for the model compound 3²⁺, NBO orbitals around the Te–Te moiety in C_i symmetry consist of a Te–Te σ-bonding orbital, a Te–C σ-bonding orbital, a lone pair orbital on the Te atom (mainly s-character), and a lone pair orbital on the Te atom (pure p-character).