New generation of nitrenium salts: catalytic hydrosilylation of imines and a mechanism of action of nitrogen Lewis acids

Nitrogen Lewis acids (NLAs) are emerging as a powerful tool in strong bond activation and catalysis. Till now, N,N-dialkyl-nitrenium salts were known and utilized in chemical transformations. In this article, we report on the synthesis and characterization of a new generation of nitrenium-based Lewis acids – N,N-diaryl-substituted naphthotriazinium salts, which open a door to libraries of stereoelectronically modifiable catalysts. We exemplify the potency of these new Lewis acidic catalysts in a gram-scale hydrosilylation of various ketimines and aldimines in yields up to 99% and a catalyst loading as low as 0.1mol%. Notably, dialkyl-nitrenium salts proved inefficient in this reaction. Based on our experimental and theoretical studies, we elucidated, for the first time, the mechanistic action of nitrenium Lewis acids in such reduction-type reactions, demonstrating a unique hydridic behavior of N-H bonds in triazanes.