Synthesis and reactivity of indium(I) 1-carba-closo-undecachlorododecaborate

The arene-solvated indium(I) species [In(C7H8)3][CHB11Cl11] (1) and [In(C6H5Br)1.5][CHB11Cl11] (2) were obtained by a redox reaction involving the silver salt Ag[CHB11Cl11] and indium powder at 80 °C in a toluene or bromobenzene solution. These thermally stable compounds react with triphenylphosphine and the N-heterocyclic carbene 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene under reduction of indium(I) to indium metal and oxidation of the ligands to phosphonium and imidazolium cations contrary to the more commonly observed disproportionation reactions. The presence of 2 equiv of carbene led to deprotonation of the anion to give the dianion [CB11Cl11](2-). Interactions of In(+) with soft donor ligands such as phosphines, olefins, alkynes, and aromatics are weak, and a crystalline solid was only obtained with the nonvolatile phosphinoacetylene Mes2PC≡CPh (Mes = 2,4,6-Me3C6H2). The structure of this compound displays In···C interactions involving the triple bond and the π system of one mesityl group but no In···P contact. Solutions of 2 in fluorobenzene also showed moderate activity as the catalyst for intramolecular hydroamination of primary and secondary aminopentenes. The new compounds were characterized by multinuclear NMR spectroscopy and X-ray diffraction for compounds 1, 2, and 4-6.