A potential role of a substrate as a base for the deprotonation pathway in Rh-catalysed C-H amination of heteroarenes: DFT insights

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The possibility of direct introduction of a new functionality through C-H bond activation is an attractive strategy in covalent synthesis. Here, we investigated the mechanism of Rh-catalysed C-H amination of the heteroaryl substrate (2-phenylpyridine) using phenyl azide as a nitrogen source by density functional theory (DFT). For the deprotocyclometallation and protodecyclometallation processes of the title reaction, we propose a stepwise base-assisted mechanism (pathway I) instead of the previously reported concerted mechanism (pathway II). In the new mechanism proposed here, 2-phenylpyridine acts as a base in the initial deprotonation step (C-H bond cleavage) and transports the proton towards the final protonation step. In fact, the N-H bond of the strong conjugate acid (formed during the initial C-H bond cleavage) considered in pathway I (via TS4) is more acidic than the C-H bond of the neutral substrate considered in pathway II (via TS5). The higher activation barrier of TS5 mainly originates from the ring strain of the four-membered cyclic transition state. The vital role of the base, as disclosed here, can potentially have broader mechanistic implications for the development of reaction conditions of transition metal-catalysed reactions
Publisher
ROYAL SOC CHEMISTRY
Issue Date
2016-05
Language
English
Article Type
Article
Citation

DALTON TRANSACTIONS, v.45, no.19, pp.7980 - 7985

ISSN
1477-9226
DOI
10.1039/c6dt00686h
URI
http://hdl.handle.net/10203/209567
Appears in Collection
CH-Journal Papers(저널논문)EEW-Journal Papers(저널논문)
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