Influence of N-Substituents on the Adsorption Geometry of OH-Functionalized Chiral N-Heterocyclic Carbenes

Shahar Dery, Peter Bellotti, Tzipora Ben-Tzvi, Matthias Freitag, Tehila Shahar, Albano Cossaro, Alberto Verdini, Luca Floreano, Frank Glorius*, Elad Gross*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Adsorption of chiral molecules on heterogeneous catalysts is a simple approach for inducing an asymmetric environment to enable enantioselective reactivity. Although the concept of chiral induction is straightforward, its practical utilization is far from simple, and only a few examples toward the successful chiral induction by surface anchoring of asymmetric modifiers have been demonstrated so far. Elucidating the factors that lead to successful chiral induction is therefore a crucial step for understanding the mechanism by which chirality is transferred. Herein, we identify the adsorption geometry of OH-functionalized N-heterocyclic carbenes (NHCs), which are chemical analogues to chiral modifiers that successfully promoted α-Arylation reactions once anchored on Pd nanoparticles. Polarized near-edge X-ray absorption fine structure (NEXAFS) measurements on Pd(111) revealed that NHCs that were associated with low enantioselectivity were characterized with a well-ordered structure, in which the imidazole ring was vertically positioned and the OH-functionalized side arms were flat-lying. OH-functionalized NHCs that were associated with high enantioselectivity revealed a disordered/flexible adsorption geometry, which potentially enabled better interaction between the OH group and the prochiral reactant.

Original languageAmerican English
Pages (from-to)10029-10035
Number of pages7
JournalLangmuir
Volume37
Issue number33
DOIs
StatePublished - 24 Aug 2021

Bibliographical note

Funding Information:
This research was partially supported by the European Research Council (ERC) under the European Unionʼs Horizon 2020 research and innovation program (Grant Agreement No. 802769, ERC Starting Grant “MapCat”). S.D. acknowledges the Israeli Ministry of Energy and the Azrieli Foundation for financial support. The authors also thank the Deutsche Forschungsgemeinschaft (Leibniz Award, SBF 858) for generous funding.

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