Polymer-supported metathesis catalysts

Metathesis catalysts including Gmbbs ruthenium catalyst (see Chap. 5) are hard to separate from the reaction products. Chemists therefore sought ways to overcome this problem by immobilizing the catalyst on various supports. Buchmeister recently reviewed various polymer-supported metathesis catalysts [54]. A few are reported here. Early, Grubbs described a phosphine-derivatized polystyrene-supported catalyst [55]... 

The First Polymer-supported Ru Catalyst for Olefin Metathesis... 

A chiral polymer-bound metathesis catalyst has been developed. The supported chiral complex 75d shows appreciable levels of reactivity and excellent enantios-electivity. " This complex 75d can be recycled and easily removed from unpurified mixtures. In the first and second cycles of the recycle experiment, almost the same reactivity has been shown. In the third cycle, high enantioselection and conversion are still obtained, but catalyst activity is notably diminished ... 

Grigg, R. and York, M. (2000) Bimetallic catalytic cascade ring-closing metathesis-intramolecular Heck reactions using a fluorous biphasic solvent system or a polymer-supported palladium catalyst. Tetrahedron Lett., 41, 7255-8. 

Only recently a selective crossed metathesis between terminal alkenes and terminal alkynes has been described using the same catalyst.6 Allyltrimethylsilane proved to be a suitable alkene component for this reaction. Therefore, the concept of immobilizing terminal olefins onto polymer-supported allylsilane was extended to the binding of terminal alkynes. A series of structurally diverse terminal alkynes was reacted with 1 in the presence of catalytic amounts of Ru.7 The resulting polymer-bound dienes 3 are subject to protodesilylation (1.5% TFA) via a conjugate mechanism resulting in the formation of products of type 6 (Table 13.3). Mixtures of E- and Z-isomers (E/Z = 8 1 -1 1) are formed. The identity of the dominating E-isomer was established by NOE analysis. 

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 7 7 Polymer-supported Otejin Metathesis Catalysts for Organic and Combinatorial Synthesis Tab. 11.3 Recycling of Ru complex (16) in the ring-closing metathesis of diene (17). 

Second Generation Recyclable Boomerang Polymer Supported Catalysts for Olefin Metathesis Application of Ardu-engo Carbene Complexes, M. Ahmed, T. Arnauld, a. G.M. Barrett, et at, Synlett 2000, 1007-1009. 

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

The First Polymer-Supported and Recyclable Chiral Catalyst for Enantioselec-tive Olefin Metathesis, K. C. Hultzsch,... 

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