Cross metathesis with acrylates: N‐heterocyclic carbene (NHC)‐ versus cyclic alkyl amino carbene (CAAC)‐based ruthenium catalysts, an unanticipated influence of the carbene type on efficiency and selectivity of the reaction

Abstract

Olefin metathesis has been widely explored as a handle for chemical diversification, a feature critical across chemical sectors. Cross metathesis (CM) with acrylic acid derivatives is an example of important but, due to the low catalyst's efficiency, industrially non‐utilized transformation. Here we report on systematic evaluation of ruthenium‐based catalysts bearing N‐heterocyclic carbene (NHC) or cyclic alkyl amino carbene (CAAC) ligands in cross metathesis with methyl acrylate. Dramatic influence of the carbene type on the reaction's efficiency and selectivity has been found. Density functional theory (DFT) calculations suggest that the kinetic selectivity is the main factor differentiating NHC‐ and CAAC‐based ruthenium complexes. Productive turnover number (TON) of 49 900 at 10 ppm loading of nitro‐substituted Hoveyda‐Grubbs complex (nitro‐Grela catalyst) was obtained in the studied reaction, representing the highest efficiency reported to date for this transformation. High efficiency and selectivity of nitro‐Grela catalyst was then utilized in cross metathesis of trans‐anethole with 2‐ethylhexyl acrylate to efficiently produce octyl methoxycinnamate (86 % yield), an antioxidant used in sunscreen formulations.

Bimolecular Coupling in Olefin Metathesis: Correlating Structure and Decomposition for Leading and Emerging Ruthenium−Carbene Catalysts

“…The N-DEP group is then too small to retard coupling, and 1-C1 Me decomposes nearly 10× faster than 1-C1 Ph . Consistent with this trend are the lower turnover numbers reported for C1 Me catalysts relative to their C1 Ph analogues in multiple contexts, ranging from ethenolysis to acrylonitrile metathesis. ,, …”

“…Consistent with this trend are the lower turnover numbers reported for C1 Me catalysts relative to their C1 Ph analogues in multiple contexts, ranging from ethenolysis to acrylonitrile metathesis. 12 , 13 , 25 …”

“…Consistent with this trend are the lower turnover numbers reported for C1 Me catalysts relative to their C1 Ph analogues in multiple contexts, ranging from ethenolysis to acrylonitrile metathesis. 12,13,25 Of note in this context is the much faster decomposition seen for 1-C2 Me , despite the presence of one relatively bulky o-i Pr substituent. Computational examination (see below) revealed that the latter in fact promotes pyridine loss to form the four-coordinate species 2-C2 Me , while being insufficient to impede coupling.…”

Recent Advances in the Domain of Cyclic (Alkyl)(Amino) Carbenes

“…[84] The comparative study of metathesis reactions catalyzed by cAAC and NHC stabilized ruthenium complexes by Kaczanowska et al shows that the efficiency and selectivity arehighly dependent on the types of carbenes. [85] It has also been shown that the cAAC stabilized ruthenium-based complexes can be employed in light-activated [86] and amine-assisted olefin metathesis. [87] cAAC stabilized lanthanoids have also been reported that show catalytic properties.…”

Durch Nitro‐ und andere elektronenziehende Gruppen aktivierte Ruthenium‐Katalysatoren für die Olefinmetathese

“…Zusammenfassend haben wir versucht, den Leser davon zu überzeugen, dass EWG-aktivierte Ruthenium-Katalysatoren die Synthese verschiedener chemischer Verbindungen in vielen Bereichen der organischen und medizinischen Chemie ermçglicht haben und weiterhin ermçglichen werden. [147] Danksagung Wird anken dem "Catalysis for the Tw enty-First Century Chemical Industry"-Projekt, durchgeführt im Rahmen des TEAM-TECH-Programms der Stiftung der Polnischen Wissenschaft, mitfinanziert von der Europäischen Union aus dem Europäischen Fonds fürr egionale Entwicklung im Rahmen des Programms "Smart Growth". Ferner sind wir Dr. Cezary Samojłowicz und Herrn Krzysztof Skowerski fürh ilfreiche Diskussionen dankbar.…”