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

Abstract

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, nBu3P, and IiPr. The N‐based Lewis acid 2 also forms an FLP with tBu3P 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 N3 analogues.

Synthesis of a Carbene-Stabilized (Diphospha)aminyl Radical and Its One Electron Oxidation and Reduction to Nonclassical Nitrenium and Amide Species

“…Because the synthesis of related carbene-stabilized triazenyl and triphosphorus radicals was accomplished by one-electron reduction of the corresponding azido and phosphonium cations, ,, and owing to the growing importance of cationic nitrenium species as potential organocatalysts and ligands, ,− the ability of 4 to act as a precursor to a phosphorus-stabilized nitrenium cation was explored. The cyclic voltammogram of 4 in THF (Figure ) revealed both the anticipated reversible oxidation wave ( E 1/2 ox = −1.09 vs Fc/Fc + ), which occurs at a significantly more positive potential than that reported for the triazyl radicals I and II (cf.…”

Stable Diporphyrinylaminyl Radical and Nitrenium Ion

“…[8,9] Very recently,the (alkyl)(amino)nitrenium ion 5 was reported to show improved reactivity towards neutral Lewis bases and was applied for frustrated Lewis pair systems. [10] These reports have suggested that stable nitrenium ions have potential as ligands and organocatalysts,i na nalogy to wellknown carbenes. [11] Herein we report ad iporphyrinylnitrenium ion as an extremely stable species despite the absence of adjacent heteroatoms and incorporation into ac yclic skeleton.…”

“…Thetriplet state of 10 was also calculated to be 42 kJ mol À1 higher in energy compared to the singlet state,inline with the observed sharp 1 HNMR spectra ( Figures S9 and 10). Efficient charge delocalization also results in shorter C meso À Nb ond lengths.T he increased double-bond character of C meso -N was also confirmed by the calculated Wiberg bond indexes:1.0614 (8), 1.3283 (9), and 1.3782 (10). [20] Comparing natural atomic charge between 8 and 9,i tw as found that the first oxidation from amine to aminyl radicals mainly occurs on the nitrogen center (Figure S9-8).…”

“…These changes are much smaller than total charge difference of + 1, indicating efficient charge delocalization over the whole p-electronic system. Efficient charge delocalization also results in shorter C meso À Nb ond lengths.T he increased double-bond character of C meso -N was also confirmed by the calculated Wiberg bond indexes:1.0614 (8), 1.3283 (9), and 1.3782 (10).…”

Investigating Tetrel based Neutral Frustrated Lewis Pairs for Hydrogen Activation

“…25,26 Recently, group 14 and group 15 LAs were introduced in FLP chemistry including tetrylium [27][28][29][30][31][32][33] and phosphonium LAs. [34][35][36][37][38][39][40][41][42][43][44] Cationic tetrylium LAs were used with amines to effect H2 activation. Especially Stannyliums were demonstrated as promising FLP LAs due to their excellent moisture tolerance leading to efficient catalytic hydrogenation protocols with a wide range of substrate scope.…”