Ionic olefin metathesis

To date a number of reactions have been carried out in ionic liquids [for examples, see Dell Anna et al. J Chem Soc, Chem Commun 434 2002 Nara, Harjani and Salunkhe Tetrahedron Lett 43 1127 2002 Semeril et al. J Chem Soc Chem Commun 146 2002 Buijsman, van Vuuren and Sterrenburg Org Lett 3 3785 2007]. These include Diels-Alder reactions, transition-metal mediated catalysis, e.g. Heck and Suzuki coupling reactions, and olefin metathesis reactions. An example of ionic liquid acceleration of reactions carried out on solid phase is given by Revell and Ganesan [Org Lett 4 3071 2002]. 

In addition to the applications reported in detail above, a number of other transition metal-catalyzed reactions in ionic liquids have been carried out with some success in recent years, illustrating the broad versatility of the methodology. Butadiene telomerization [34], olefin metathesis [110], carbonylation [111], allylic alkylation [112] and substitution [113], and Trost-Tsuji-coupling [114] are other examples of high value for synthetic chemists. 

Such cases are not uncommon, but full quantitative treatments are rare, since often relatively large amounts of Y must be added to obtain measurable effects. Complications may then arise from the effects of the added Y on the nature of the medium (see Chapters 2 and 3). These are particularly notable when Y and I are charged, as is often the case. Under those circumstances, maintenance of the constant ionic strength of the medium with a known non-participating ionic species is essential. The classic case of common ion depression in solvolysis of benzhydryl chloride is dealt with in Chapter 2. A more recent example of this kind of treatment with neutral reactants occurs in the elucidation of the mechanism of olefin metathesis [20], catalysed by the ruthenium methylidene 9, Scheme 9.6. With ca. 5% of 9, disappearance of diene 10 was clearly not first order. However, reactions run in the presence of large excesses of phosphine 11 were much slower and showed first-order kinetics. The plot of kQ K against 1/ [ 11 ] was linear, consistent with dissociation of 9 to yield an active catalytic species prior to engagement with the diene, with k t [11] 3 > fc2[diene]. Because first-order kinetics were observed under these conditions, determination of order with respect to the catalytic species (as well as the diene) was simplified, and an outline for the mechanism could be constructed (see also Chapter 12 for more detailed consideration of catalysed olefin metathesis). 

Olefin isomerization, with Claisen rearrangement, 1, 365 Olefin metathesis with alkyllead, 9, 415 in aqueous media, 1, 834 ESI—MS studies, 1, 812 in high-throughput catalyst discovery, 1, 365 in ionic liquids, 1, 869 for polymerization characteristics, 1, 149 Grubbs catalysts, 1, 151 Schrock catalysis, 1, 150... 

CHAPTER 8 Ionic Addition of HX to an Alkene 332 Free-Radical Addition of HBr to Alkenes 334 Acid-Catalyzed Hydration of an Alkene 338 Oxymercuration of an Alkene 340 Hydroboration of an Alkene 345 Addition of Halogens to Alkenes 350 Formation of Halohydrins 352 Epoxidation of Alkenes 360 Acid-Catalyzed Opening of Epoxides 362 Olefin Metathesis 376... 

As in many other areas of catalysis in ionic liquids, the research of the past years in ionic liquid supported olefin metathesis has been dominated by demonstrating the general feasibility in this reaction medium. With the development of the task-specific complexes new prospects have been opened and the improved recyclability of these compounds relative to the common metathesis catalysts is impressive. Apart from more active and stable catalysts, the development of enantioselective catalysts and of continuous processes are likely to be the next goals. 

Yao, Q., Zhang, Y. Olefin metathesis in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate using a recyclable Ru catalyst Remarkable effect of a designer ionic tag. Angew. Chem., Int. Ed. Engl. 2003,42, 3395-3398. 

Sledz P, Mauduit M, Grela K (2008) Olefin metathesis in ionic liquids. Chem Soc Rev 37 2433-2442... 

Buijsman RC, vem Vuuren E, Sterrenburg JG (2001) Ruthenium-catalyzed olefin metathesis in ionic liquids. Org Lett 3 3785-3787... 

Audic N, Clavier H, Mauduit M, Giiillemin JC (2003) An ionic liquid-supported ruthenium carbene complex a robust and recyclable catalyst for ring-closing olefin metathesis in ionic liquids. J Am Chem Soc 125 9248-49... 

Wakamatsu H, Saito Y, Masubuchi M, Fujita R (2008) Synthesis of imidazoUum-tagged ruthenium carbene complex remarkable activity and reusability in regard to olefin metathesis in ionic liquids. Synlett 1805-1808... 

EPR spectroscopy has been applied by Kucherov and coworkers to study the nature of the catalyticaUy active species in [W +(Mo"+) - ionic liquids - olefin] metathesis systems [77]. In this study the key role of isolated paramagnetic complexes of W + and Mo + ions in the catalytic metathesis of 1-hexene could be demonstrated. It... 

Wu B, Wen J, Zhang J, Li J, Xiang YZ, Yu XQ (2009) One-pot Van Leusen synthesis of 4,5-disubstituted oxazoles in ionic liquids. Synlett 3(137) 500-504 Wakamatsu H, Saito Y, Masubuchi M, Fujita R (2008) Synthesis of imidazolium-tagged ruthenium carbene complex remarkable activity and reusability in regard to olefin metathesis in ionic liquids. Synlett 2008 1805-1808... 

Capitalizing on our efforts aimed at developing more environment friendly olefin metathesis processes, we have describe recently synthesis of new air-stable pyridinium containing Ru catalysts 15 for which the ionic tag is anchored to the styrenyl-ether benzylidene fragment (Figure 8). 

Abstract Olefin metathesis has found a tremendous number of application in the past 25 years. Immobilisation of olefin metathesis (pre)catalysts in room temperature ionic liquids (RTILs) offers the opportunity to recover and reuse the catalyst and also to reduce the level of ruthenium (Ru) contaminants in the products. 

Keywords olefin metathesis, ruthenium catalysts, ionic liquids, catalyst recycling. 

Olefin metathesis in ionic liquids 2.1 What are Ionic liquids ... 

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