Ruthenium catalyst for olefin metathesis

A Novel Class of Ruthenium Catalysts for Olefin Metathesis, T. Weskamp,... 

W. C. SCHATTENMANN, M. SpiEGLER, et at, Angew. Chem. 1998, 110, 2631-2633 Angew. Chem. Int. Ed. 1998, 37, 2490-2493 (b) Highly Active Ruthenium Catalysts for Olefin Metathesis The Synergy of N-Heterocyclic Carbenes and Coordi-natively Labile Ligands, T. Weskamp,... 

J. Wolf, W. Stuer, C. Grunwald, H. Werner, P. Schwab, and M. Schulz, Ruthenium Trichloride, Tricyclohexylphosphane, 1-Alkynes, Magnesium, Hydrogen, and Water-Ingredients of an Efficient One-Pot Synthesis of Ruthenium Catalysts for Olefin Metathesis, Angew. Chem. Int. Ed. 37, 1124-1126 (1998). 

J. C. Conrad, D. Amoroso, P. Czechura, G. P. A. Yap, andD. E. Fogg, The First Highly Active, Halide-Free Ruthenium Catalyst for Olefin Metathesis, Organometallics 22, 3634-3636 (2003). 

Figure 333 Achiral and chiral ruthenium catalysts for olefin metathesis reactions.

Grubbs catalyst (Section 26.6) A widely used ruthenium catalyst for olefin metathesis that has the structure Cl2(Cy3P)2Ru=CHPh. 

Occhipinti G, Bjorsvik H-R, Jensen VR. Quantitative Structure-Activity Relationships of Ruthenium Catalysts for Olefin Metathesis. J Am Chem Soc. 2006 128(21) 6952-6964. 

Weskamp, T., Kohl, F.J., Herrmann, W.A., WHeterocyclic carbenes novel ruthenium-alkylidene complexes, J. Organomet Chem. 1999,582 362—365. Weskamp, T., Kohl, F.J., Hieringer, W., Gleich, D., Herrmann, W. A., Highly active ruthenium catalysts for olefin metathesis the synergy of 7V-heterocyclic carbenes and coordinatively labile ligands, Angew. Chem. Int. Edit. 1999, 38 2416-2419. 

Weskamp, T., Schattenmann, W.C., Spiegler, M., Herrmann, W.A., A novel class of ruthenium catalysts for olefin metathesis, Angew. Chem. Int. Edit 1998, 37 2490-2493. 

The mechanistic investigations presented in this section have stimulated research directed to the development of advanced ruthenium precatalysts for olefin metathesis. It was pointed out by Grubbs et al. that the utility of a catalyst is determined by the ratio of catalysis to the rate of decomposition [31]. The decomposition of ruthenium methylidene complexes, which attribute to approximately 95% of the turnover, proceeds monomolecularly, which explains the commonly observed problem that slowly reacting substrates require high catalyst loadings [31]. This problem has been addressed by the development of a novel class of ruthenium precatalysts, the so-called second-generation catalysts. 

Olefin-metathesis is a useful tool for the formation of unsaturated C-C bonds in organic synthesis.186 The most widely used catalysts for olefin metathesis include alkoxyl imido molybdenum complex (Schrock catalyst)187 and benzylidene ruthenium complex (Grubbs catalyst).188 The former is air- and moisture-sensitive and has some other drawbacks such as intolerance to many functional groups and impurities the latter has increased tolerance to water and many reactions have been used in aqueous solution without any loss of catalytic efficiency. 

Together with Schrock s molybdenum-imido compound 50 ° the ruthenium-phosphine complexes 51 and especially 52 developed by Grubbs " proved to be an outstanding achievement in the development of molecular catalysts for olefin metathesis reactions (Scheme 10). 

The in situ preparation of a ruthenium-alkylidene catalyst for olefin metathesis is the first step for extending this high-throughput approach toward other catalytic transformations and opens up the way to the screening of azolium salt libraries for olefin metathesis reactions. ... 

Title Alkylidene Complexes of Ruthenium Containing A-Heterocyclic Carbene Ligands Use as Highly Active, Selective Catalysts for Olefin Metathesis... 

With the discovery of ruthenium carbene complexes as highly effective catalysts for olefin metathesis under mild reaction conditions [233,234], the scope of ring-opening metathesis polymerization could be extended to include functionalized and sensitive monomers. The resulting (soluble) polymers have been used as supports for simple synthetic transformations [235-237]. Insoluble polymers have been prepared by ringopening metathesis copolymerization of norbornene with l,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene. These polymers have been used as supports for ruthenium carbene complexes [238]. 

The first introduction of NHC ligands to ruthenium complexes for olefin metathesis catalysts was reported by Hermann et al. in 1998 [58]. These derivatives exhibit two unsaturated NHC ligands (20) and show little improvement in activity when compared to the parent bis(phosphine) complex 1 (Fig. 2). Due to the stronger a-donor ability of NHCs compared to phosphines, catalyst initiation by dissociation of one NHC is disfavored. Subsequently, the synthesis of phosphine-NHC complex 2 that contains a bulkier NHC ligand was reported by different research groups [2-5]. This complex... 

A family of phosphine-free ruthenium-based olefin metathesis catalysts has been developed over the last few years. First, work done independently by Hoveyda and Blechert resulted in the H2Mes isopropoxybenzylidene (4b), a highly active air-stable ruthenium (pre)catalyst for olefin metathesis (Scheme 4). Hoveyda described (4b) as a recyclable monomeric catalyst also with high activity for ring-opening, ring-closure, and cross metathesis that tolerates... 

One of the most widely used catalysts for olefin metathesis is the ruthenium complex shown. It is called Grubb s catalyst and abbreviated Cl2(PCy3)2Ru=CHC6H5. 

Ruthenium-carbene complexes of the type [RuCl2(=CHRXPR 3)2] are extraordinarily useful catalysts for olefin metathesis. Furthermore, they have unique properties, e.g. high tolerance towards atmospheric oxygen, functional groups and moisture. 

Richard Schrock investigated the properties of some of the first catalysts for olefin metathesis. His work included catalysts prepared from tantalum, titanium, and molybdenum. The catalysts predominandy in use today, however, are ruthenium catalysts developed by Robert Grubbs. His so-called first generation and second generation catalysts are shown here. 

Only development of ruthenium-based catalysts has allowed tolerance to a singular functional group to operate without requiring experiments to be conducted under an inert atmosphere [5]. They can be used with substrates that carry an alcohol, a carboxylic acid, or an aldehyde, but can be rendered inactive in the presence of structurally exposed amines and phosphines. The reverse is true for molybdenum-based catalysts, but they are generally more active than ruthenium catalysts, and demand preparation and handling under an inert atmosphere [1]. Table 5.1 is a summary of the functional-group tolerance of some general catalysts for olefin metathesis [8]. 

Poater A, Ragone F, Correa A, Cavallo L. Comparison of different ruthenium-alkylidene bonds in the activation step with N-heterocyclic carbene Ru-catalysts for olefins metathesis. Dalton Trans. 2011 40 11066-11069. 

Furstner, A., Guth, O., Duffels, A., Seidel, G., Liebl, M., Gabor, B., Mynott, R., Indenylidene complexes of ruthenium optimized synthesis, structure elucidation, and performance as catalysts for olefin metathesis—application to the synthesis of the ADE-ring system of Nakadomarin A, Chem. Eur. J. 2001, 7 4811-4820. 

Ruthenium s supremacy in the carbene chemistry of Group 8 elements is a direct consequence of the tremendous interest raised by NHC-Ru complexes as catalysts for olefin metathesis. Indeed, the synergy of a late transition metal tolerant of a wide variety of functional groups, together with a class of ligands whose physical and chemical properties are easily modulated to tailor the activity, selectivity, stability, water-solubility, recoverability, or latency of the resulting catalytic species, translated into an unprecedented success story of modern synthetic chemistry. Yet, the ability of ruthenium complexes to promote carbon-carbon bond formation goes well beyond... 

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