Premium
Ionic Pd/NHC Catalytic System Enables Recoverable Homogeneous Catalysis: Mechanistic Study and Application in the Mizoroki–Heck Reaction
Author(s) -
Eremin Dmitry B.,
Denisova Ekaterina A.,
Yu. Kostyukovich Alexander,
Martens Jonathan,
Berden Giel,
Oomens Jos,
Khrustalev Victor N.,
Chernyshev Victor M.,
Ananikov Valentine P.
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201903221
Subject(s) - catalysis , homogeneous , heck reaction , ionic bonding , chemistry , palladium , ionic liquid , organic chemistry , ion , thermodynamics , physics
N‐Heterocyclic carbene (NHC) ligands are ubiquitously utilized in catalysis. A common catalyst design model assumes strong M–NHC binding in this metal–ligand framework. In contrast to this common assumption, we demonstrate here that lability and controlled cleavage of the M−NHC bond (rather than its stabilization) could be more important for high‐performance catalysis at low catalyst concentrations. The present study reveals a dynamic stabilization mechanism with labile metal–NHC binding and [PdX 3 ] − [NHC‐R] + ion pair formation. Access to reactive anionic palladium intermediates formed by dissociation of the NHC ligands and plausible stabilization of the molecular catalyst in solution by interaction with the [NHC‐R] + azolium ion is of particular importance for an efficient and recyclable catalyst. These ionic Pd/NHC complexes allowed for the first time the recycling of the complex in a well‐defined form with isolation at each cycle. Computational investigation of the reaction mechanism confirms a facile formation of NHC‐free anionic Pd in polar media through either Ph–NHC coupling or reversible H–NHC coupling. The present study formulates novel ideas for M/NHC catalyst design.