455948-11-5Relevant 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)
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.
Synthesis, structure, and activity of enhanced initiators for olefin metathesis
Love, Jennifer A.,Sanford, Melanie S.,Day, Michael W.,Grubbs, Robert H.
, p. 10103 - 10109 (2003)
A series of ruthenium olefin metathesis catalysts of the general structure (H2IMes)(PR3)(Cl)2-Ru=CHPh (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) ylidene) have been prepared; these complexes are readily accessible in two steps from commercially available (H2IMes)(PCY3)(Cl)2Ru=CHPh. Their phosphine dissociation rate constants (k1), relative rates of phosphine reassociation, and relative reaction rates in ring-opening metathesis polymerization (ROMP) and ring-closing metathesis (RCM) have been investigated. The rates of phosphine dissociation (initiation) from these complexes increase with decreasing phosphine donor strength. Complexes containing a triarylphosphine exhibit dramatically improved initiation relative to (H 2IMes)(PCy3)(Cl)2Ru=CHPh. Conversely, phosphine reassociation shows no direct correlation with phosphine electronics. In general, increased phosphine dissociation leads to faster olefin metathesis reaction rates, which is of direct significance to both organic and polymer metathesis processes.
Solvents for ring-closing metathesis reactions
Adjiman, Claire S.,Clarke, Adam J.,Cooper, Gregory,Taylor, Paul C.
, p. 2806 - 2808 (2009/02/04)
A study of the influence of eight diverse solvents on a Grubbs II-catalysed ring-closing metathesis (RCM) reaction reveals a complex dependence of the different reaction steps on the solvent and suggests acetic acid as a useful solvent for RCM reactions. The Royal Society of Chemistry.
