Ruthenium Complexes Featuring Unsymmetrical N‐Heterocyclic Carbene Ligands–Useful Olefin Metathesis Catalysts for Special Tasks

Abstract

This review describes a distinct class of ruthenium olefin metathesis catalysts featuring unsymmetrical N-heterocyclic carbene (uNHC) ligands, from its historical beginning to the present state of the art. Thanks to advantageous traits, such as pronounced thermodynamic stability, chemical latency, outstanding selectivity, and compatibility with green solvents, these catalysts led to good results in a number of specialized metathesis transformations. Therefore, while being a niche, the uNHC complexes can potentially be implemented in a number of industrial processes, such as valorization of Fischer-Tropsch olefin fractions, ethenolysis of renewable products, and modern pharmaceutical production.

Testing enabling techniques for olefin metathesis reactions of lipophilic substrates in water as a diluent

“…diethyl 3-methylcyclopent-3-ene-1,1-dicarboxylate (12) 172.4, 137.4, 121.3, 61.4, 59.4, 44.6, 40.8, 16.0, 14.0. Presented analytical data are consistent with literature (Monsigny et al, 2021a(Monsigny et al, , 2021b. 9, 30.4, 27.3, 22.3, 14.0.…”

“…9, 30.4, 27.3, 22.3, 14.0. Presented analytical data are consistent with literature (Che et al, 2009;Monsigny et al, 2021aMonsigny et al, , 2021b).…”

“…2, 136.2, 125.9, 125.8, 124.7, 124.2, 123.2, 122.3, 111.6, 54.0, 53.4; melting point: 216 C. Presented analytical data are consistent with literature (Nienałtowski et al, 2020b). pyrazolo[4,3-d]pyrimidin-7-one (24) 1, 153.6, 146.9, 146.5, 138.3, 131.3, 131.0, 130.5, 125.5, 124.5, 121.1, 113.1, 66.0, 55.0, 38.2, 27.7, 22.3, 14.6, 14.0; melting point: 187 C. Presented analytical data are consistent with literature (Monsigny et al, 2021a(Monsigny et al, , 2021b. 7, 130.4, 128.5, 128.4, 125.9, 38.9, isomer Z: 140.8, 129.0, 128.5, 128.46, 125.9, 33.5.…”

“…This result is supported by higher stability and productivity generally observed for catalysts possessing a bulkier SIPr (1,3-bis-(2,6-triisopropylphenyl)-2-imidazolidinylidene) ligand in the structure (Clavier et al, 2009). Subsequently, we investigated the activity of catalyst Ru4 with an unsymmetrically substituted NHC ligand (uNHC) (Monsigny et al, 2021a) and, unfortunately, we noted low substrate conversion (Table 1, entry 4). In the next attempt, CAAC derivatives Ru5, Ru6, and Ru7 exhibiting relatively high protic solvent tolerance were tested (Blanco et al, 2021;Nagyha ´zi et al, 2020).…”

Encapsulation of the Hoveyda–Grubbs 2nd generation catalyst in magnetically separable alginate/mesoporous carbon beads for olefin metathesis reactions in water

“…Olefin metathesis is a valuable and versatile tool for the construction of advanced molecular architectures in an efficient manner. 1 The discovery of ruthenium-based air and moisture stable Grubbs and Hoveyda–Grubbs catalysts have led to the development of diverse metathetic and non-metathetic transformation reactions in organic solvents. 2 Despite the air and moisture stability of Grubbs catalysts, adapting olefin metathesis reactions into water media is an ongoing challenge due to the hydrophobic nature of both olefinic substrates and Grubbs catalysts.…”