Cationic Triarylchlorostibonium Lewis Acids.

Organopnictogen cations show promise as powerful, tunable main-group Lewis acid catalysts. The synthesis, solid-state structures, and reactivity of a series of weakly coordinated triarylchlorostibonium salts [Ar 3 SbCl][B(C 6 F 5 ) 4 ] (Ar = Ph, 3-FC 6 H 4 , 4-FC 6 H 4 , 3,5-F 2 C 6 H 3 , 2,4,6-F 3 C 6 H 2 ) are reported. The cation in each adopts a tetrahedral coordination environment of antimony, with near complete separation from the anion. Structural, computational, and reactivity studies reveal that the Lewis acidity of [Ar 3 SbCl] + generally increases with increased fluorination of the Ar substituents, with a secondary quenching effect from para fluorination. [Ar 3 SbCl] + is reduced to Ar 3 Sb in the presence of Et 3 SiH, and the mechanism of this reaction has been modeled computationally. Preliminary studies demonstrate that they are useful catalysts for the dimerization of 1,1-diphenylethylene and the Friedel-Crafts alkylation of benzene.