Grubbs-Hoveyda ruthenium

A Grubbs-type ruthenium complex and a Hoveyda ruthenium complex were compared under similar conditions for recycled activity. Both the reference catalysts showed a large drop in metathesis activity in the subsequent tests. For example, a Grubbs-type ruthenium alkylidene catalyst showed a drop of nearly 50% conversion in the second run. 

Epimerization of vinylcyclopropanes by Grubbs I-type ruthenium catalysts (28) has been explored.33 The reaction can also be effected by the Grubbs-Hoveyda catalyst (29) provided that an additional phosphine is added. Mechanistic studies (experimental and theoretical) suggest that the epimerization goes through a ruthenacyclopentene intermediate (30). 

Chiral silver complexes bearing bidentate NHC ligands (24) have been synthesized. They are used in alkene metathesis and allylic alkylation reactions high diastereos- (g) electivity is observed induced by the chiral backbone on the prochiral biphenyl.27 Ruthenium-based complexes obtained from transmetalation with a Grubbs-Hoveyda complex exhibited high activities and enantioselectivities in ring-opening metathesis/ ... 

The simpler architecture is the 1,1 -biphenyl scaffold, likewise introduced by Hoveyda and coworkers [19]. The synthesis of the imidazolium salt starts with a chiral diamine and a substituted, achiral biphenyl [82-84], Subsequent introduction of a Mes substituent on the remaining primary amino end and ring closure reaction yields the chiral saturated imidazolium salt after hydrolysation of the methoxy group to liberate the phenolic hydroxy group (see Figure 4.22). Reaction with silver(I) oxide and carbene transfer to a Grubbs (Hoveyda) catalyst sets up the ruthenium catalyst complex. 

Olefin metathesis reaction that reorganizes carbon-carbon double bonds provides fundamentally new strategies for natural product synthesis and polymer chemistry. Hilvert and coworkers built up an artificial metalloenzyme by covalently tethering a Grubbs-Hoveyda-type Ru complex to a protein scaffold [78]. An /V-heterocyclic carbene (NHC) ligand, which has been reported as a suitable ligand for a number of water-soluble ruthenium-based metathesis catalysts, was derivatized with an electrophilic bromoacetamide. The Ru carbene complex (27 in Figure 10.16) was then attached by site-selective alkylation of the cysteine... 

For a review of asymmetric Mo-catalyzed metathesis, see Catalytic Asymmetric Olefin Metathesis, A. H. Hoveyda, R. R. ScHROCK, Chem. Eur. J. 2001, 7, 945-950 for reports on chiral Ru-based complexes, see (b) Enantioselective Ruthenium-Catalyzed Ring-Qosing Metathesis, T.J. Sei-DERS, D.W. Ward, R.H. Grubbs, Org. Lett. 2001, 3, 3225-3228 (c) A Recyclable Chiral Ru Catalyst for Enantioselective Olefin Metathesis. Efficient Catalytic Asymmetric Ring-Opening/Cross Metathesis In Air, J. J. Van Veldhuizen, S. B. 

The most widely used catalysts for RCM are Grubbs ruthenium catalyst 9 and its second generation analogue 10, as well as first and second generation Hoveyda-Grubbs catalysts 11 and 12 (Fig. 6) [38]. The latter have superior stability and reactivity, expanding the applicability of the method considerably. Schrock molybdenum catalyst 13 has also been described for macrocy-clization [38]. 

Furthermore Grubbs et al. have published water-soluble as well as chiral ruthenium alkylidene complexes based on 16 for ARCM and AROM, whereas Schrock, Hoveyda and coworkers have synthesized a variety of asymmetric molybdenum alkylidene complexes, e.g. (5)-17 17,27 addition Hoveyda et al. have synthesized the achiral ruthenium complex 18 and the chiral complex 19 for ARCM and AROM. 

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