Halogenated rhenacarboranes: optoelectronic behavior of the iodinated rhenacarborane complex anion [3,3,3-(CO)3-8-I-closo-3,1,2-ReC2B9H10]

Treatment of the long-known compound Cs3,3,3-(CO)₃-closo-3,1,2-ReC₂B₉H₁₁] with N(C₆H₄Br-4)₃]SbCl₆] in the presence of Me₃NO in THF (tetrahydrofuran) has led to the formation of HNMe₃]3,3-(CO)₂-3,3-Cl₂-closo-3,1,2-ReC₂B₉H₁₁] in good yield. Structural characterization of this compound has identified it as a four-legged piano stool half-sandwich complex anion resulting from oxidation of rhenium by both the aminium and hexachloroantimonate ions and CO displacement promoted by Me₃NO in the presence of by-product chloride ions. Direct iodination of Cs3,3,3-(CO)₃-closo-3,1,2-ReC₂B₉H₁₁] has yielded 3,3,3-(CO)₃-3-I-closo-3,1,2-ReC₂B₉H₁₁], which undergoes iodide migration in donor solvents from the metal to the β-B vertex in the coordinating face of the cage. The resulting complex anion, 3,3,3-(CO)₃-8-I-closo-3,1,2-ReC₂B₉H₁₀]⁻, whose structure has been confirmed by X-ray diffraction, has been shown to be luminescent in MeTHF at 77 K (λ_em = 455 nm) and electroactive in solution at ambient temperatures, undergoing a quasi-reversible two-electron oxidation to a proposed Re^III cationic rhenacarborane species in MeCN solutions. By contrast, two fully reversible sequential one-electron oxidations have been observed in CH₂Cl₂ solutions.