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 Cs[3,3,3-(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 Cs[3,3,3-(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 (λem = 455 nm) and electroactive in solution at ambient temperatures, undergoing a quasi-reversible two-electron oxidation to a proposed ReIII cationic rhenacarborane species in MeCN solutions. By contrast, two fully reversible sequential one-electron oxidations have been observed in CH2Cl2 solutions.