Olefins olefin-metathesis catalyst

The outstanding performances of five-membered NHC ligands in organometallic chemistry and catalysis prompted Grubbs and co-workers to develop a novel stable four-membered NHC [64]. Following their interest in developing new ruthenium olefin metathesis catalysts, they synthesised and fully characterised complex 51 to study the impact of the architecturally unique NHC ligand on the activity of the Ru-based catalyst [65] (Fig. 3.20). In the RCM of 1 at 40°C in CH Cl with 51 (5 mol% catalyst), the reaction reached completion within 20 min, whereas less than 10 min are required for standard catalysts 14 and 16. It should be noted that catalysts 14 and 16 are able to complete the RCM of 1 with only 1 mol% catalyst at 30°C. 

Ruthenium-Based Second Generation Olefin Metathesis Catalysts and Their Application... 

An alternative approach has been formulated by Katz and co-workers (28). They consider the latent cis specificity in reactions of c/ s-olefins with metathesis catalysts to be quite high, based on their results with a catalyst having very low Lewis acidity. They further propose that the frequently observed lack of stereospecificity is mainly the consequence of cationic processes inherent in the metathesis step which mask stereospecificity. 

Imidazole-containing reagents have found useful applications in a variety of organic transformations. A second generation of ruthenium-based olefin metathesis catalysts... 

Quite recently, ruthenium carbene complexes more typically known as olefin metathesis catalysts have been shown to act as alkyne hydrosilylation catalysts.78,79 7Vzz r-addition is the major product with trialkylsilanes, even in a single example with an internal alkyne.78 This result represents one of the very few examples of fra r-hydrosilylation of internal alkynes. 

Poly (acetylenes) [16], There are several catalysts available for polymerization of substituted acetylenes. Whereas Ziegler-Natta catalysts are quite effective for polymerization of acetylene itself and simple alkylacetylenes, they are not active towards other substituted acetylenes, e.g. phenylacetylenes. Olefin-metathesis catalysts (Masuda, 1985 Masuda and Higashimura, 1984, 1986) and Rh(i) catalysts (Furlani et al., 1986 Tabata, 1987) are often employed. In our experience, however, many persistent radicals and typical nitrogen-containing functional groups serve as good poisons for these catalysts. Therefore, radical centres have to be introduced after construction of the polymer skeletons. Fortunately, the polymers obtained with these catalysts are often soluble in one or other organic solvent. For example, methyl p-ethynylbenzoate can be polymerized to a brick-coloured amorph- See the Appendix on p. 245 of suffixes to structural formula numbers. 

Despagnet-Ayoub E, Ritter T (2006) N-Heterocyclic Carbenes as Ligands for Olefin Metathesis Catalysts. 2f 193-218... 

Polymer-supported Olefin Metathesis Catalysts for Organic and Combinatorial Synthesis... 

I 11 Polymer-supported Olefin Metathesis Catalysts for Organic and Combinatorial Synthesis Tab. 11.6 Catalytic olefin metathesis with Ru complex (41). ... 

The Syntheses and Activities of Polystyrene-Supported Olefin Metathesis Catalysts Based on Cl2(PCy3)2Ru = CH-CH=CPh2, S.T. Nguyen, R.H. Grubbs, J. Organomet. Chem. 1995, 497, 195-200. 

Well-Defined Ruthenium Olefin Metathesis Catalysts Mechanism and Activity, ... 

Synthesis and Activity of a New Generation of Ruthenium-Based Olefin Metathesis Catalysts Coordinated with 1,3-Dime-sityl-4,5-dihydroimidazol-2-ylidene Ligands, M. Scholl, S. Ding, C.W. Lee, et al, Org. Lett. 1999, 7, 953-956. 

Recent mechanistic work has shown that 16 e Ru methylene complexes (such as bisphosphine 11) are slow to re-enter the catalytic cycle. Their reluctance to initiate can result in competitive decomposition see Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts, M.S. Sanford, J.A. Love, R.H. Grubbs,/. 

Synthesis and Application of a Permanently Immobilized Olefin Metathesis Catalyst, S.C. Schurer, S. Gessler, N. Buschmann, et al, Angew. Chem. 2000,... 

Simply Assembled and Recyclable Polymer-Supported Olefin Metathesis Catalysts, L. Jafarpour, S.P. Nolan, Org. Lett. 2000, 2, 4075-4078. 

Immobilization of Olefin Metathesis Catalysts on Monolithic Sol-Gel. Practical, Efficient, and Easily Recyclable Catalysts for Organic and Combinatorial Synthesis, J.S. Kingsbury, S. B. Garber,... 

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