Ca Stabilized by Carborate Anions: Synthesis, Structure, and Reactivity.

The syntheses of calcium carborates, Ca[HexCBCl], 1, Ca[HCBCl], 2, and Ca[MeCBCl]·2(o-DFB), 3·2(o-DFB), (o-DFB = 1,2-difluorobenzene) including the structure of 2·4(o-DFB) are described. The large size of the Ca cation is reflected by the coordination geometry with the Ca center being coordinated by three Cl donors from each of the carborate anions and one F donor from each of the two coordinated solvent molecules. Based on B NMR and DOSY NMR studies, the salts 1, 2 and 2·2(o-DFB) form close ion pairs in PhBr and o-DFB solutions. The Fluoride Ion Affinities (FIA) in PhBr for the salts 1 and 2·2(o-DFB) were DFT-calculated (ωB97XD/6-31 + G**) at 211.3 kJ mol and 217.5 kJ mol, respectively, which is below that of the landmark Lewis acid B(CF) (241.5 kJ mol). The Ca center in salt 1 is sufficiently Lewis acidic to coordinate 1,5-cyclooctadiene (1,5-COD) and 2,6-octadiyne and to catalyze the hydrosilylation of 1-hexene and several alkynes, albeit slowly. Compound 1 also displays moderate activity as a catalyst for transfer hydrogenation catalysis and carbonyl-olefin metathesis (COM), a first for Ca compounds.