Stable Mg ²⁺ Dication Weakly Stabilized/Coordinated in Solution: Synthesis, Structure, Reactivity, and Use in Catalysis

Abstract The first soluble and stable Mg 2+ dication stabilized only by weakly coordinating and chemically robust carborate anions [HexCB 11 Cl 11 ] − is described. Mg[HexCB 11 Cl 11 ] 2 ( 1 ), prepared by reaction of Mg( n Bu) 2 with 2 equiv of [Ph 3 C][HexCB 11 Cl 11 ], consists, in the solid state, of a central Mg 2+ surrounded by two [HexCB 11 Cl 11 ] − anions. In solution, experimental and classical molecular dynamics simulations (cMD) agree with cation/anion association being retained, reflecting the high electrophilicity of the Mg center. Yet, reflecting only weak anion/cation interactions, species 1 polymerizes 1‐hexene and coordinates alkynes. However, 1 displays no reaction with HSiEt 3 at room temperature, consistent with a low hydridicity of the hard (HSAB) Mg 2+ center. Contrasting with 1 (FIA = 264 kJ mol −1 ; FIA: Fluoride Ion Affinity), salt Mg[( n Bu) 3 NB 12 H 4 Cl 7 ] 2 ( 2 ), incorporating the more basic ammoniododecaborate [( n Bu) 3 NB 12 H 4 Cl 7 ] − anion, is significantly less Lewis acidic (FIA = 214.7 kJ mol −1 ) and unreactive with alkenes and alkynes. Salt 1 effectively catalyzes alkene/alkyne hydrosilylation via an initial alkene/alkyne coordination/initiation, as suggested by experimental and computational data. It also efficiently catalyzes (with a catalyst loading down to 0.1 mol%) the hydrosilylation of CO 2 to CH 4 in the presence of HSiEt 3 . Salt 1 smoothly promotes the catalytic transfer hydrogenation of 1,1‐diphenylethylene, and it is also an active imine hydrogenation catalyst in the presence of H 2 .