We report a combined experimental and computational investigation of the Suzuki–Miyaura cross-coupling of amides enabled by [Pd(NHC)(allyl)Cl] precatalysts. Most crucially, mechanistic details pertaining to the Pd/NHC catalytic cycle were elucidated by computational methods. Mechanistic insights shed light on the role of each ligand about the metal. Sterics play a key role in the initial activation of the catalyst. As a key insight, we have shown that water participates in the activation of the Pd-NHC catalytic system. Easier activation has led to effect room temperature cross-coupling of a broad range of amides through selective N−C bond scission under the mildest conditions reported to date. The use of sterically hindered [Pd(IPr*)(cin)Cl] reported herein for the first time in the amide cross-coupling indicates that increasing flexible steric bulk of the isopropyl wingtip groups of the NHC ligand provides a modular scaffold for promoting amide cross-coupling in high yields. The precatalytic pathway involving both NHC ligands as well as the catalytic cycle beginning from the Pd species are discussed. The mechanistic details provide insight into the amide bond twist (distortion) that leads to N−C cross-coupling reactions and is required for the efficient N−C bond activation.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): OSR-2015-CCF-1974-03
Acknowledgements: A.P. thanks the Spanish MINECO for a project CTQ2014-59832-JIN, and EU for a FEDER fund (UNGI08-4E-003). Rutgers University and the NSF (CAREER CHE-1650766) are gratefully acknowledged for support (M.S.). The Bruker 500 MHz spectrometer was supported by the NSF-MRI grant (CHE-1229030). P.L. thanks the China Scholarship Council for a fellowship (No. 201606350069). SPN thanks the ERC, King Saud University and King Abdullah University of Science and Technology (Award No. OSR-2015-CCF-1974-03) for support.