Alkene Metathesis and Related Reactions

1-undecanoate, allyltrimethylsilane, allyl bromide, and methyl oleate occur readily whereas a sluggish reaction was obtained with the corresponding heterogeneous catalysts prepared via NH4Re04 and NH4Re04/SnMe4 [11]. 

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Grubbs RH, Pine SH. 9.3—Alkene metathesis and related reactions. In Heming BMT, editor. Comprehensive organic synthesis. Oxford Pergamon 1991. p. 1115—27. 

R H. Grubbs, R. H. Pine, Alkene Metathesis and Related Reactions in Comprehensive Organic Synthesis. (Ed. B. M. Trost), Pergamon, New York, 1991,5, 1115-1127. 

Since that discovery there has been much interest in this photochemical reaction, which produces a catalyst working in mild conditions without an organometallic component [1-23]. The same catalyst induces the metathesis of acyclic alkenes [1-17] and the ringopening metathesis polymerisation (ROMP) of cyclic olefins studied recently by Sundararajan et al. [18, 22, 23], as well as the polymerisation of various substituted acetylenes investigated by Masuda et ai [13, 19]. I was first of all intrigued to know what intermediates are formed in the above photochemical reaction and which one is the true catalyst in metathesis and related reactions. 

Insights from Computational Studies on d° Metal-Catalyzed Alkene and Alkyne Metathesis and Related Reactions... 

Besides alkene or alkyne metathesis, a broad range of other non-metathetical reactions promoted by NHC Ru complexes was reported in the literature. " Some of them were discovered serendipitously, as they constituted side reactions in metathesis catalysis. Other were deliberately investigated and optimised. Despite the usefiilness of several of these processes, their significance has remained undervalued due to the huge appeal of olefin metathesis and related reactions. 

The general reaction equation for alkene metathesis in a simple system, cross-metathesis of two different disubstituted alkenes, is depicted in Scheme 1. In this reaction, a transition metal catalyst establishes equilibrium between the starting alkenes, the ( )- and (Z)-stereoisomers of all possible substituent combinations, and ethylene. Related reaction processes have also been reported for alkynes (aikyne metathesis) and for combinations of alkenes and alkynes (enyne metathesis). Aikyne metathesis is less well developed compared to alkene metathesis and enyne metathesis. This review has been organized according to the basic modes of metathesis depicted in Scheme 2. Alkene metathesis is the more developed process and numerous examples of all the variants have been reported. Aikyne metathesis is less well developed and three variants exist aikyne cross-metathesis, aikyne metathesis polymerization, and ring-closing aikyne metathesis. 

An impoftant series of catalytic reactions involve some of the intennediates and padiways discussed in previous chapters. Alk ie metathesis (Eq. 12.1), now gaining wide acceptance in organic and polymer synthesis, goes via metal cathene intermediates, Alkene polymerization, a key modem development in polymer synthesis, uses unsaturated alkyl complexes. This catalytic reaction allows an exceptional level of control over the molecular structure and therefore over the polymer properties. The water-gas shift and related reactions are of commercial importance in providing a simple route to H2 and to acetic acid. C—H activation refers to a class of catalytic reactions in which unactivated C-H bonds are broken. Finally, we look at some organometallic materials. 

Although the transformation of a primary alkyne into a vinylidene complex, 2, in presence of a number of transition metal systems is well reported [2, 3], only rare examples are known for the transformation of an alkene into a carbene complex [4, 5]. Given the increased role played by vinylidene and carbene complexes as key partners in metathesis reactions and related catalytic processes [6, 7], opening up new efficient and easy synthetic routes to such complexes is an important challenge. 

Ruthenium is not an effective catalyst in many catalytic reactions however, it is becoming one of the most novel and promising metals with respect to organic synthesis. The recent discovery of C-H bond activation reactions [38] and alkene metathesis reactions [54] catalyzed by ruthenium complexes has had a significant impact on organic chemistry as well as other chemically related fields, such as natural product synthesis, polymer science, and material sciences. Similarly, carbonylation reactions catalyzed by ruthenium complexes have also been extensively developed. Compared with other transition-metal-catalyzed carbonylation reactions, ruthenium complexes are known to catalyze a few carbonylation reactions, such as hydroformylation or the reductive carbonylation of nitro compounds. In the last 10 years, a number of new carbonylation reactions have been discovered, as described in this chapter. We ex-... 

Alkenylsilanes, mainly vinyl silanes and allyl silanes or related compounds, being widely used intermediates for organic synthesis can be efficiently prepared by several reactions catalyzed by transition-metal complexes, such as dehy-drogenative silylation of alkenes, hydrosilylation of alkynes, alkene metathesis, silylative coupling of alkenes with vinylsilanes, and coupling of alkynes with vinylsilanes [1-7]. Ruthenium complexes have been used for chemoselective, regioselective and stereoselective syntheses of unsaturated products. 

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