Unhindered Biplane-Shaped N-Heterocyclic Carbene Ligands as a Remedy for Low Reactivity of Crowded Substrates in Ruthenium Catalyzed Olefin Metathesis

31 July 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Despite notable progress, olefin metathesis methods for preparing sterically crowded C-C double bonds remain scarce. They are commonly based on specialized ruthenium catalysts with sterically reduced N-heterocyclic carbene (NHC) ligands, able to accommodate more crowded olefinic sub-strates during the catalytic steps. Yet, although being highly active, these complexes are rather unstable, mainly due to intramolecular C-H activation at the ortho position of an N-aryl group of the NHC ligand, leading to catalyst deactivation. Considering that the deleterious C-H activation process requires the rotation of the N-aryl arm of the NHC ligand, we introduced a second decker of aromatic groups in benzimidazolylidene-based N-phenyl NHC ligands, which leads to robust and highly efficient ruthenium metathesis catalysts in challenging metathesis reactions of tri-and tetra-substituted olefins. The beneficial effect of these upper aromatic “wings” on the stability and activity of the Ru-complexes is rationalized through the experimental determination of the stereoelectronic properties of the NHC ligands, complemented by DFT calculations on the nature of the through-space interactions between the aromatics and on the decomposition pathway of the second-generation Hoveyda precursors.


Olefin Metathesis
Ruthenium Catalysts
N-Heterocyclic Carbene
Catalyst Design
Tetrasubstituted Double Bond Formation

Supplementary materials

Supporting Information
Experimental details


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Comment number 1, Karol Grela: Apr 22, 2024, 10:05

Raw data supporting this paper can be directely dowload from https://hal.science/hal-04542322v1/file/Raw%20data-20240411T062459Z-001.zip