Catalyst, olefin metathesis

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... 

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... 

The formation of carbon-carbon bonds using olefin metathesis methodology is a powerful technique in fine organic synthesis and polymer chemistry. The increasing importance of these reactions is reflected by the numerous publications over the last few years. Many of these pubhcations deal with the design and apphca-tion of polymer-supported olefin metathesis catalysts with the aim to overcome the common drawbacks of the homogeneous catalysts low thermal stability and difficulties associated with their recovery from the reaction mixtures. The modem state of art in this important field is described in chapter 11 of this volume. 

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. 

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