Nitrogen-Based Lewis Acids: Synthesis and Reactivity of a Cyclic (Alkyl)(Amino)Nitrenium Cation

摘要

A room-temperature-stable crystalline cyclic (alkyl)(amino)nitrenium cation 2 features cationic nitrogen atom with a smaller HOMO-LUMO gap compared to that of a 1,2,3-triazolium 5 (an N-heterocyclic nitrenium cation). The low-lying LUMO of 2 results in an enhanced electrophilicity, which allowed for the formation of Lewis adducts with neutral Lewis bases, such as Me3P, nBu(3)P, and IiPr. The N-based Lewis acid 2 also forms an FLP with tBu(3)P but subsequently reacts with (PrS)(2) to cleave the S-S bond. Both experimental and theoretical results suggest that the Lewis acidity of 2 is stronger than its N-3 analogues.