First Main-Group Element Lewis Acid Thionyl Chloride Adduct and its Chemistry

Although the adduct of aluminum trichloride with thionyl chloride has been reported, no thionyl chloride adduct of a main group element Lewis acid or organometallic compound has been structurally characterized. In this communication we present the synthesis and reactivity of the structurally ascertained adduct of thionyl chloride with tris(pentafluoroethyl)gallane as a representative of a main group element Lewis acid. Gallium and indium compounds with electron withdrawing groups, e.g. the pentafluoroethyl ligand, display versatile properties. While gallates and indates, [MR₄]^-, behave as weakly coordinating anions, neutral gallanes and indanes, MR₃, are strong Lewis acids. Salts with the tetrakis(pentafluoroethyl)gallate and -indate, [M(C₂F₅)₄]^- (M=Ga, In), have recently been studied in detail. In contrast to this, work on the syntheses of the free Lewis superacids M(C₂F₅)₃ (M=Ga, In) is scarce and underdeveloped. The hydrates [M(C₂F₅)₃(OH₂)₂] proved to be suitable starting materials, particularly due to their thermal stability. Herein we report on synthesis and characterization of reactive adducts, [M(C₂F₅)₃D], with the weak donor molecules (D) SOCl₂ and Me₃SiF. The effective Lewis acidities of Ga(C₂F₅)₃ and In(C₂F₅)₃ were experimentally determined by the (modified) Gutmann-Beckett method and their catalytic potential is showcased.