CH Activation of Cationic Bismuth Amides: Heteroaromaticity, Derivatization, and Lewis Acidity
Kai Oberdorf, Patrick Grenzer, Nele Wieprecht, Jacqueline Ramler, Anna Hanft, Anna Rempel, Andreas Stoy, Krzysztof Radacki, Crispin Lichtenberg
Abstract
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.