Lewis Acidic Telluronium Cations: Enhanced Chalcogen-Bond Donor Properties and Application to Transfer Hydrogenation Catalysis

We describe the synthesis and structures of o-C₆F₄(TeMes)₂ (1) and o-C₆F₄(TeAr^F)₂ (2, Ar^F = 3,5-(CF₃)₂C₆H₃)), two new bifunctional tellurides featuring an electron-withdrawing backbone. While 2 resisted methylation, 1 reacted with Me₃O·BF₄ in CH₂Cl₂ to afford o-C₆F₄(TeMes)­(TeMeMes) ([3]⁺), a mixed-valent telluride/telluronium cation isolated as a tetrafluoroborate salt. Although attempts to methylate the second telluride have been unsuccessful, [3]⁺ readily catalyzes the hydrogenation of 2-phenyl-quinoline with Hantzsch ester. Comparison with simple telluronium cations including [Ar^F₂TeMe]⁺ and [MesAr^FTeMe]⁺ confirms that the catalytic activity of these compounds originates from the presence of a tetravalent, cationic tellurium center.