CH Activation of Cationic Bismuth Amides: Heteroaromaticity, Derivatization, and Lewis Acidity

Cationization of Bi(NPh2)(3) has recently been reported to allow access to single- and double-CH activation reactions, followed by selective transformation of Bi-C into C-X functional groups (X = electrophile). Here we show that this approach can successfully be transferred to a range of bismuth amides with two aryl groups at the nitrogen, Bi(NR2aryl)(3). Exchange of one nitrogen-bound aryl group for an alkyl substituent gave the first example of a homoleptic bismuth amide with a mixed aryl/alkyl substitution pattern at the nitrogen, Bi(NPhiPr)(3). This compound is susceptible to selective N-N radical coupling in its neutral form and also undergoes selective CH activation when transformed into a cationic species. The second CH activation is blocked due to the absence of a second aryl moiety at nitrogen. The Lewis acidity of neutral bismuth amides is compared with that of cationic species [Bi(aryl)(amide)(L)(n)](+) and [Bi(aryl)(2)(L)(n)](+) based on the (modified) Gutmann-Beckett method (L = tetrahydrofuran or pyridine). The heteroaromatic character of [Bi(C6H3R)(2)NH(triflate)] compounds, which are iso-valence-electronic with anthracene, is investigated by theoretical methods. Analytical methods used in this work include nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction, mass spectrometry, and density functional theory calculations.

Automated summary

The cationization of Bi(NPh2)(3) for single- and double-CH activation reactions has been successfully applied to bismuth amides with two aryl groups at the nitrogen, resulting in the first example of a homoleptic bismuth amide with a mixed aryl/alkyl substitution pattern. The Lewis acidity of neutral bismuth amides was compared with that of cationic species using the Gutmann-Beckett method. The heteroaromatic character of [Bi(C6H3R)(2)NH(triflate)] compounds was investigated by theoretical methods, revealing their iso-valence-electronic nature with anthracene.