title: A potential role of a substrate as a base for the deprotonation pathway in Rh-catalysed C-H amination of heteroarenes: DFT insights.
abstract: 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) is more acidic than the C-H bond of the neutral substrate considered in pathway II (via). The higher activation barrier of 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.
authors.affiliation: Graduate School of EEWS, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea. aji.john07@gmail.com ysjn@kaist.ac.kr and KAUST Catalysis Center and Division of Physical Sciences & Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
authors.forename: Manjaly J
authors.initials: MJ
authors.lastname: Ajitha
authors.affiliation: KAUST Catalysis Center and Division of Physical Sciences & Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
authors.forename: Kuo-Wei
authors.initials: KW
authors.lastname: Huang
authors.affiliation: Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 305-701, Korea and Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea.
authors.forename: Jaesung
authors.initials: J
authors.lastname: Kwak
authors.affiliation: Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 305-701, Korea and Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea.
authors.forename: Hyun Jin
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 305-701, Korea and Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea.
authors.forename: Sukbok
authors.initials: S
authors.lastname: Chang
authors.affiliation: Graduate School of EEWS, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea. aji.john07@gmail.com ysjn@kaist.ac.kr.
authors.forename: Yousung
authors.initials: Y
authors.lastname: Jung