Catalyst Decomposition during Olefin Metathesis Yields Isomerization‐Active Ruthenium Nanoparticles

Abstract

The second‐generation Grubbs catalyst, RuCl2(H2IMes)(PCy3) (=CHPh) [GII; H2IMes=1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene, Cy=cyclohexyl], is shown to decompose during olefin metathesis to generate Ru nanoparticles (RuNPs). These RuNPs appear to contribute significantly to competing isomerization during metathesis. Larger, partially oxidized RuNPs are also observed in commercial GII, but these exhibit modest isomerization activity. Removal of RuNPs from the precatalyst does not prevent isomerization, because new, more reactive NPs are generated by catalyst decomposition during metathesis.

N‐Heterocyclic Olefin‐Ligated Palladium(II) Complexes as Pre‐Catalysts for Buchwald–Hartwig Aminations

“…As such, an additional catalyst poisoning experiment using substoichiometric amounts of PMe 3 was conducted. By using substoichiometric amounts of poisoning phosphine in relation to the Pd present, further support can be offered for the presence of catalytic palladium colloids because the bulk of palladium present in these nanoparticles is buried in the core of the particles, so small amounts of poisoning ligand will halt catalysis . Again, PMe 3 was added 30 minutes into the reaction time and a similar halt in catalysis was noted (Figure ), thus adding further support for the initial presence of catalytically active Pd nanoparticles.…”

In a Quest for Selectivity Paired with Activity: A Ruthenium Olefin Metathesis Catalyst Bearing an Unsymmetrical Phenanthrene‐Based N‐Heterocyclic Carbene

“…Diminished isomerisation during a metathesis process is usually connected with higher stability of a given Ru alkylidene propagating species . One of the factors affecting the rate of decomposition is the presence of ethylene, as it is known that ruthenium methylidenes are the least stable active species …”

“…It has been reportedf or years, that isomerisation is related to ruthenium hydride complexes which emerge from ab imolecular decomposition of the propagating ruthenium complexes. [70][71][72] Later,i naseries of detailed studies by Fogg, [73][74][75][76][77] Nelson and Percy [78] it has been shown that non-hydride Rucomplexes,shall be considered. Recently,one of the commonly suspected Ru-hydride species, [71,79] was shown to be kinetically incompetent to account for isomerization during metathesis.…”

Ruthenium Complexes Bearing Thiophene‐Based Unsymmetrical N‐Heterocyclic Carbene Ligands as Selective Catalysts for Olefin Metathesis in Toluene and Environmentally Friendly 2‐Methyltetrahydrofuran

“…These types of substrates are known to be prone to migration of the double bond along the carbon chain, especially when the second‐generation Ru catalysts are used. This undesired side process is induced by catalyst decomposition products, mainly ruthenium hydrides and dimers, and even Ru nanoparticles . The most common solution for this difficulty is the application of various additives, including: metallic mercury, quinones, chlorocatecholborane, or phenylphosphoric acids, however, none of them are universal.…”

“…This undesired side process is induced by catalyst decomposition products, mainly ruthenium hydrides and dimers, and even Ru nanoparticles . The most common solution for this difficulty is the application of various additives, including: metallic mercury, quinones, chlorocatecholborane, or phenylphosphoric acids, however, none of them are universal. Recent developments in this field have shown that the application of specialized Ru‐complexes with either unsymmetrical NHC ligands or quinones built into the catalyst structure can significantly reduce the double bond migration during the metathesis reaction, providing selectivity levels ≥90 %.…”