Schrock molybdenum-alkylidene complex

Ring-closing metathesis reaction of allenynes occurs at room temperature in the presence of a Schrock molybdenum-alkylidene complex to give ring-closed... 

Although numerous advantages are associated with the use of supercritical carbon dioxide (scC02) as an ecologically benign and user friendly reaction medium, systematic applications to metal-catalyzed processes are still rare. A notable exception is a recent report on the use of scC02 for the formation of industrially relevant polymers by ROMP and the eyelization of various dienes or enynes via RCM [7]. Both Schrock s molybdenum alkylidene complex 24 and the ruthe-... 

Murakami et al. reported a ring-closing metathesis reaction of allenynes using Schrock s molybdenum alkylidene complex [37]. Treatment of allenynes ISl with a catalytic amount of the complex 15 2 in toluene at rt gave cyclopentene derivatives 1 S3 in good yield. Two possible reaction mechanisms were proposed, one through a vinylidene complex 154 and the other through a carbene complex, but based on several mechanistic studies, they favored the vinylidene complex pathway, which is shown here (Scheme 5.42). 

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. 

Heppekausen J, Piirstner A. Rendering schrock-type molybdenum alkylidene complexes air stable user-friendly precatalysts for alkene metathesis. Angew Chem Int Ed. 2011 50(34) 7829-7832. 

In spite of its versatility, metathesis could not, until lately, be developed to its full synthetic potential because the traditional catalysts were ill-suited for application being relatively short-hved and susceptible to air, moisture, or side reactions. Schrock was the first to develop an entire family of tungsten-alkylidene and, more importantly, molybdenum-alkylidene complexes with very high activity and selectivity in olefin metathesis. Further on, Grubbs discovered ruthenium (Ru) catalysts which up to now are among the most tolerant of functional groups initiators. ... 

The proposed idea that metal alkyhdene complexes are be able to catalyze olefin metathesis was confirmed in 1980 [8] and consolidated in 1986 by Schrock with the development of the first well-characterized, highly active, neutral tungsten (Cl, Fig. 3) [9] and molybdenum (C2) [10] alkylidene complexes. These complexes were able to catalyze both the metathesis of different olefins and the ROMP of functionalized norbomene to polynorbomene with low polydispersities [11]. Moreover, these catalysts were used by Wagener and coworkers to perform the first quantitative ADMET polymerization [12] and copolymerization [13] of 1,5-hexadiene and 1,9-decadiene. However, the low stability of these catalysts in... 

Fig. 3 Olefin metathesis catalysts Schrock tungsten (Cl) and molybdenum (C2) alkylidene complexes, Grubbs first- (C3) and second-generation (C4) catalysts, Hoveyda-Grubbs second-generation catalyst (C5), and Grubbs third-generation catalyst (C6)...

Connon SJ, Blechert S. Recent developments in olefin crossmetathesis. Angew. Chem., Int. Ed. 2003 42 1900-1923. Schrock RR, Hoveyda AH. Molybdenum and mngsten imido alkylidene complexes as efficient olefin-metathesis catalysts. Angew. Chem. Int. Ed. 2003 42 4592-4633. 

The first metal alkylidene complexes for alkene metathesis with a defined molecular structure were the molybdenum-based complex 14 prepared by Schrock in 1990 and the ruthenium-based complex 15 synthesized by Grubbs in 1995. 

Schrock, R. R. Recent advances in olefin metathesis by molybdenum and tungsten imido alkylidene complexes. J. Mol. Catal. A Chemical... 

A significant development for the selective synthesis of alkenes makes use of alkene metathesis. Metathesis, as applied to two alkenes, refers to the transposition of the alkene carbon atoms, such that two new alkenes are formed (2.110). The reaction is catalysed by various transition-metal alkylidene (carbene) complexes, particularly those based on ruthenium or molybdenum. The ruthenium catalyst 84, developed by Grubbs, is the most popular, being more stable and more tolerant of many functional groups (although less reactive) than the Schrock molybdenum catalyst 85. More recently, ruthenium complexes such as 86, which have similar stability and resistance to oxygen and moisture as complex 84, have been found to be highly active metathesis catalysts. 

R.R. Schrock and A.H. Hoveyda (2003) Angewandte Chemie International Edition, vol. 42, p. 4592 - Molybdenum and tungsten imido alkylidene complexes as efficient olefin-metathesis catalysts . 

Schrock, R.R., Muidzek, J.S., Bazan, G.C., Robbins, J., Dimare, M., Oregan, M., Synthesis of molybdenum imido alkylidene complexes and some reactions involving acyclic olefins, J. Am. Chem. Soc. 1990, 112 3875-3886. 

Synthesis of the main family of Schrock s molybdenum-imido-alkylidene complexes... 

R.R. Schrock, A.H. Hoveyda - Molybdenum and Tungsten Imido Alkylidene Complexes as Efficient Olefin-Metathesis Catalysts,... 

Schrock, R. R., Murdzek, J. S., Bazan, G. C., Robbins, J., DiMare, M and O Regan, M B. Synthesis of Molybdenum Imido Alkylidene Complexes and Some Reactions Involving Acyclic Olefins. JAm Chem Soc 112, 3875-3886 (1990). 

Initial reports of cross-metathesis reactions using well-defined catalysts were limited to simple isolated examples the metathesis of ethyl or methyl oleate with dec-5-ene catalysed by tungsten alkylidenes [13,14] and the cross-metathesis of unsaturated ethers catalysed by a chromium carbene complex [15]. With the discovery of the well-defined molybdenum and ruthenium alkylidene catalysts 3 and 4,by Schrock [16] and Grubbs [17],respectively, the development of alkene metathesis as a tool for organic synthesis began in earnest. 

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