Ionic-liquid-based synthesis of tellurium–rhenium carbonyls with specific reaction control

Abstract

The novel tellurium rhenium carbonyls [TeI₂Re(CO)₅][AlCl₄] (1), [BMIm][Te₂I₄(μ-I)₂Re(CO)₄] (2), {Te₃I₂(μ-I)₃(μ₃-I)}Re(CO)₃ (3) and [BMIm][(Te₂)₃{Re(CO)₃}₂{Re(CO)₄}₃] (4) were prepared by reacting TeI₄ and Re₂(CO)₁₀ in ionic liquids (ILs). [TeI₂Re(CO)₅][AlCl₄] (1) was obtained in a mixture of [BMIm]Cl (BMIm: 1-butyl-3-methylimidazolium) and AlCl₃ (ratio: 1 : 1) and contains a [TeI₂Re(CO)₅]⁺ cation. Increasing the amount of AlCl₃ ([BMIm]Cl : AlCl₃ = 1 : 2) results in [BMIm][Te₂I₄(μ-I)₂Re(CO)₄] (2) with the anion [Te₂I₄(μ-I)₂Re(CO)₄]⁻. At a [BMIm]Cl to AlCl₃ ratio of 1 : 3, {Te₃I₂(μ-I)₃(μ₃-I)}Re(CO)₃ (3) was realized with a Te₃I₃ ring and μ₃-coordinating iodine. Finally, [BMIm][(Te₂)₃{Re(CO)₃}₂{Re(CO)₄}₃] (4) was prepared in [BMIm][OTf] (OTf: triflate) and contains the ufosan-like anion [(Te₂)₃{Re(CO)₃}₂{Re(CO)₄}₃]⁻ with three Te₂²⁻ and two Re(CO)₃⁺ units that establish a distorted heterocuban-like cage. The compounds were characterized by single-crystal structure analysis, energy dispersive X-ray (EDX) analysis, thermogravimetry (TG), and infrared spectroscopy (FT-IR). The course of the reaction and the formation of the four novel tellurium-rhenium carbonyls can be directly correlated to the reaction conditions and especially to the acidity of the IL.