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(NRaryl2)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)2NH­(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.