778649-59-5Relevant articles and documents
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.
