No abstract

Cationic Al(III) and Ga(III) species supported by N-heterocyclic carbene (NHC) ligands, (IDipp)AlMe 2 (PhBr)] + ([1] + , IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2ylidene) and (IDipp)GaMe 2 ] + ([2] + ), were prepared and structurally characterized as B(C 6 F 5 ) 4 salts via ionization of the corresponding neutral precursors (IDipp)MMe 3 (M = Al, Ga) with [Ph 3 C][B(C 6 F 5 ) 4 ] in PhBr at room temperature. Both [1][B(C 6 F 5 ) 4 ] and [2][B(C 6 F 5 ) 4 ] salt were isolated in high yield and their solid state structures established through X-ray crystallographic studies. Cations [1] + and [2] + , which are rare examples of structurally characterized tris-organyl Al(III) and Ga(III) cations, stand as potent Lewis acids as experimentally estimated through the Gutmann-Beckett method. These cations were further exploited in hydrosilylation catalysis of alkynes, benzaldehyde and CO 2 using HSiEt 3 as an hydrosilane source. Hydrosilylation of 1-hexyne, 4-phenylbutyne and phenylacetylene led to the formation of the corresponding Z-selective products 3-5, respectively, while benzaldehyde was converted to PhCH 2 OSiEt 3 (6). Cations [1] + and [2] + also slowly catalyze CO 2 hydrosilylation with the selective formation of the methanol-equivalent MeOSiEt 3 .