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

Paweł Krzesiński (1, 2) , Chiara Dinoi (3) , Iker Del rosal (3) , Laure Vendier (2) , Stéphanie Bastin (2) , Vincent César (2) , Anna Kajetanowicz (1) , Karol Grela (1)

1 UW - University of Warsaw
2 LCC - Laboratoire de chimie de coordination
3 LPCNO - Laboratoire de physique et chimie des nano-objets

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.

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

Domains: Catalysis; Coordination chemistry; Organic chemistry

Paweł Krzesiński, Chiara Dinoi, Iker Del rosal, Laure Vendier, Stéphanie Bastin, et al.. Unhindered Biplane-Shaped N-Heterocyclic Carbene Ligands as a Remedy for Low Reactivity of Crowded Substrates in Ruthenium Catalyzed Olefin Metathesis. 2024. ⟨hal-04542322⟩