Alkene metathesis catalysis

Carbenes are both reactive intermediates and ligands in catalysis. They occur as intermediates in the alkene metathesis reaction (Chapter 16) and the cyclopropanation of alkenes. As intermediates they carry hydrogen and carbon substituents and belong therefore to the class of Schrock carbenes. As ligands they contain nitrogen substituents and are clearly Fischer carbenes. They have received a great deal of attention in the last decade as ligands in catalytic metal complexes [58], but the structural motive was already explored in the early seventies [59],... 

In the field of alkene metathesis ruthenium-allenylidene precursors have made, since 1998, an important contribution to catalysis [12, 31, 32], for the formation of cycles and macrocycles via RCM, ROMP and acyclic diene metathesis (ADMET) polymerization. 

C. Bruneau, and P. H. Dixneuf, Metal Yinylidenes and Allenylidenes in Catalysis Applications in Anti-Markovnikov Additions to Terminal Alkynes and Alkene Metathesis, Angew. Chem. Int. Ed. 45, 2176-2203 (2006). 

Dimetallocycles have been discovered which exhibit high reactivity with respect to carbon-carbon bond-making and -breaking processes. They allow the synthesis of a variety of simple but important hydrocarbon ligands bridging a dinuclear metal centre. y-Carbene complexes are readily available by several routes and their reactions have implications for both alkyne polymerisation and alkene metathesis. A substantial chemistry of organic species co-ordinated at dinuclear metal centres is in prospect, with significance for metal surface chemistry and catalysis. 

Molybdenum compounds play a significant role in industrial catalysis, in particular, in alkene metathesis, ammoxi-dation, epoxidation, hydrodesulfinization, hydroformylation, and in chemical and photooxidation processes. Molybdenum is also an essential trace element encountered in a wide variety of enzymes. These enzymes are responsible for the growth and health of organisms, and the cycUc of nitrogen, sulfur, and carbon in the bio-geo-spheres. ... 

Red ReOs, which can be obtained by CO reduction of the heptaoxide at 175 280 °C, is a good electrical conductor with a metal-like temperatme dependence the d electron is clearly delocalized. It has octahedral Re and easily forms nonstoichiometric bronzes in which an alkali metal donates an electron to the metal-0x0 lattice and enters the stmetme as a cation. Supported ReOs is important in alkene metathesis catalysis. No Tc analog is known. Blue Re20s, brown Re02, and black Rc203 are also known. For Tc, the only lower oxide is TCO2. 

Alkene metathesis catalysis involves intermediates in which a transition metal is multiply bonded to carbon. These species are often referred to as nucleophilic caibenes when the carbon atom is negatively polarized. A more functional description is to name these compounds as alkylidene complexes, since they react to transfer an alkylidene moiety from a transition metid to a substrate carbon atom. Previous sections of this chapter have focused on a common example of this chemistry the process of metathesis that involves transition metal mediated interaction of carbon-carbon multiple bonds. 

In the field of homogeneous catalysis the metathesis of unsaturated hydrocarbons offers many intriguing possibilities for producing important intermediates and end products from alkenes and alkynes. Through major advances in catalyst design in recent years, metathesis has become an important synthetic route to be considered in chemical laboratories whenever a special organic product has to be obtained. In fine chemistry metathesis is a very valuable reaction for the synthesis of natural compounds. Metathetical polymerization has been accepted by the industry as a viable means for producing polymers. 

Chapter 26 Homogeneous catalysis alkene (olefin) metathesis 789... 

Metal vinylidenes and allenylidenes in catalysis of anti-Markovnikov additions to terminal alkynes and alkene metathesis, particularly with participation and/or formation of heterocycles 06AG(E)2176. 

S meril, D. Olivier-Bourbigou. H. Bruneau, C. Dixneuf, P.H. Alkene metathesis catalysis in ionic liquids with ruthenium allenylidene salts. Chem. Commun. 2002. 146-147. 

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