Water Adducts of the Lewis Superacids: Tris(pentafluoroethyl)gallane and ‐indane

Herein we report on the synthesis of tris(pentafluoroethyl)indane, In(C₂F₅)₃. It is accessible in the form of its dihydrate [In(C₂F₅)₃(OH₂)₂]. An improved synthesis for the gallium analogue [Ga(C₂F₅)₃(OH₂)₂] is also reported. Due to their stability and convenient accessibility, the hydrates are ideal starting compounds for the chemistry of tris(pentafluoroethyl)gallium and -indium compounds, for example hydroxogallates and -indates.

Abstract

Lewis superacids (LSA) are defined by a fluoride ion affinity (FIA) that exceeds that of SbF₅, and are thus characterized as hard according to the HSAB concept. Soft superacidity was defined for compounds exceeding the hydride ion affinity (HIA) of B(C₆F₅)₃. Herein we report on the synthesis of a Lewis acid being superacidic only on the soft regime: tris(pentafluoroethyl)indane, In(C₂F₅)₃. It is accessible in the form of its dihydrate [In(C₂F₅)₃(OH₂)₂]. An improved synthesis for the gallium analogue [Ga(C₂F₅)₃(OH₂)₂] is also reported. Tris(pentafluoroethyl)indane dihydrate, [In(C₂F₅)₃(OH₂)₂], was fully characterized by IR and NMR spectroscopy, as well as by single crystal X-ray diffraction. Due to their stability and convenient accessibility, the hydrates are ideal starting compounds for the chemistry of tris(pentafluoroethyl)gallium and -indium compounds, for example hydroxogallates and -indates. An attempt to determine its gas-phase structure and that of the gallium analogue by electron diffraction demonstrates that they lose water ligands upon evaporation. The energetics of these processes were predicted by quantum-chemical calculations as was the nature of bonding in the free Lewis acids and their mono- and dihydrates. Furthermore, the synthesis and structural diversity of hydroxido tris(pentafluoroethyl) gallates and one indate are presented.

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