Molecular Adsorbates Switch on Heterogeneous Catalysis: Induction of Reactivity by N-Heterocyclic Carbenes

Johannes B. Ernst†, Christian Schwermann‡, Gen-ichi Yokota§, Mizuki Tada§∥⊥, Satoshi Muratsugu*§ , Nikos L. Doltsinis*‡, and Frank Glorius*† 

† Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany

‡ Institute for Solid State Theory and Center for Multiscale Theory and Computation, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany

§Department of Chemistry, Graduate School of Science, ∥Research Center for Materials Science (RCMS), and ⊥Integrated Research Consortium on Chemical Sciences (IRCCS), Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi 464-8602, Japan

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/jacs.7b05112

Abstract

We report the N-heterocyclic carbene (NHC)-induced activation of an otherwise unreactive Pd/Al2O3 catalyst. Surface analysis techniques demonstrate the NHC being coordinated to the palladium particles and affecting their electronic properties. Ab initio calculations provide further insight into the electronic effect of the coordination with the NHC injecting electron density into the metal nanocluster thus lowering the barrier for bromobenzene activation. By this NHC modification, the catalyst could be successfully applied in the Buchwald–Hartwig amination of aryl chlorides, bromides, and iodides. Various heterogeneity tests could additionally show that the reaction proceeds via a heterogeneous active species.