533934-20-2Relevant academic research and scientific papers
Allenyl esters as quenching agents for ruthenium olefin metathesis catalysts
Roy, Animesh,Silvestri, Maximilian A.,Hall, Robert A.,Lepore, Salvatore D.
supporting information, p. 106 - 108 (2016/12/23)
In the attempt to synthesize substituted allenyl esters through a metathesis coupling of unsubstituted allenyl esters and alkenes using a variety of ruthenium catalysts, it was discovered that allenyl esters themselves cleanly arrested the activity of the catalysts. Further studies suggests possible utility of allene esters as general quenching agents for metathesis reactions. To explore this idea, several representative olefin metathesis reactions, including ring closing, were successfully terminated by the addition of simple allenyl esters for more convenient purification.
Decomposition of a Phosphine-Free Metathesis Catalyst by Amines and Other Bronsted Bases: Metallacyclobutane Deprotonation as a Major Deactivation Pathway
Ireland, Benjamin J.,Dobigny, Bernadette T.,Fogg, Deryn E.
, p. 4690 - 4698 (2015/08/18)
Reactions are described of the second-generation Hoveyda catalyst HII with amines, pyridine, and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), in the presence and absence of olefin substrates. These nitrogen bases have a profoundly negative impact on metathesis yields, but in most cases, they are innocuous toward the precatalyst. HII adducts were formed by primary and secondary amines (n-butylamine, sec-butylamine, benzylamine, pyrrolidine, morpholine), pyridine, and DBU at room temperature. No reaction was evident for NEt3, even at 60 °C. On longer reaction at RT, unencumbered primary amines abstract the benzylidene ligand from HII. With 10 equiv of NH2nBu, this process was complete in 12 h, affording NHnBu(CH2Ar) (Ar = o-C6H4-OiPr) and [RuCl(H2IMes)(NH2nBu)4]Cl. For benzylamine, benzylidene abstraction occurred over days at RT. No such reaction was observed for sec-butylamine, secondary amines, NEt3, pyridine, or DBU. All of these bases, however, strongly inhibited metathesis of styrene by HII, with a general trend toward more deleterious effects with higher Bronsted basicity. Studies at 10 mol % of HII and 10 equiv of DBU, NEt3, and pyrrolidine (60 °C, C6D6) indicated that the primary mechanism for decomposition involved base-induced deprotonation of the metallacyclobutane intermediate, rather than the Lewis base-mediated decomposition pathways previously established for the Grubbs catalysts. In the corresponding metathesis of ethylene, this decomposition process is rapid even at RT, highlighting the vulnerability of the less substituted metallacyclobutane.
Ortho- and para-substituted Hoveyda-Grubbs carbenes. An improved synthesis of highly efficient metathesis initiators
Bujok, Robert,Bieniek, Michal,Masnyk, Marek,Michrowska, Anna,Sarosiek, Agata,Stepowska, Halszka,Arlt, Dieter,Grela, Karol
, p. 6894 - 6896 (2007/10/03)
A novel highly efficient and general route to various 3- and 5-substituted 2-alkoxystyrenes, required for the preparation of Hoveyda-Grubbs catalysts, is described.
CHELATING CARBENE LIGAND PRECURSORS AND THEIR USE IN THE SYNTHESIS OF METATHESIS CATALYSTS
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, (2008/06/13)
Chelating ligand precursors for the preparation of olefin metathesis catalysts are disclosed. The resulting catalysts are air stable monomeric species capable of promoting various metathesis reactions efficiently, which can be recovered from the reaction mixture and reused. Internal olefin compounds, specifically beta-substituted styrenes, are used as ligand precursors. Compared to terminal olefin compounds such as unsubstituted styrenes, the beta-substituted styrenes are easier and less costly to prepare, and more stable since they are less prone to spontaneous polymerization. Methods of preparing chelating-carbene metathesis catalysts without the use of CuCl are disclosed. This eliminates the need for CuCl by replacing it with organic acids, mineral acids, mild oxidants or even water, resulting in high yields of Hoveyda-type metathesis catalysts. The invention provides an efficient method for preparing chelating-carbene metathesis catalysts by reacting a suitable ruthenium complex in high concentrations of the ligand precursors followed by crystallization from an organic solvent.
