Richard Schrock plenary lecture Olefin metathesis catalysts LinkedIn
I. Chain-extending. This brings together two olefins to make a longer chain molecule, an example being the CM of 1-octene with itself to produce 7-octadecene and ethylene gas.
However, their work did not address what happens between olefins.
In 1973 Grubbs found further evidence for this mechanism by isolating one such metallacycle not with tungsten but with by reaction of the dilithiobutane with cis-bis(triphenylphosphine)dichloroplatinum(II)
A large number of examples of using cross metathesis in total synthesis have been published. In a recent example, Nicolau’s group used cross metathesis in the total synthesis of an analog of the natural product Biyouyanagin A. A trisubstituted olefin (type III) was reacted with 5eq of 1,4-diacetoxybutene. The final product was produced with remarkable chemo- and stereoselectivity in 73% yield. No products arising from cross metathesis of any of the other double bonds present was observed. (J. Am. Chem. Soc. 2008, 130, 11114).
Grubbs wrote about his first ruthenium catalyst [
Early development and design of these catalysts highlighted 2 main systems, a Molybdenum-based one and a Ruthenium-based one. The Molybdenum system, mainly developed by Schrock and his group, is highly active to a broad range of substrate but has limited tolerance to certain functional groups and has high air and moisture sensitivity, making its use more limited. The Ruthenium system, mainly developed by Grubbs and his group, is less reactive than the Molybdenum system but is more tolerant to a variety of functional groups and is less air sensitive.
Synthesis of a Triazole-Linked C-Disaccharide as a Case Study
To prevent backbiting in this or other systems you must make sure your catalyst does not react with internal olefins!When the reaction is complete, there are two methods for cleaving the polymer from the metal center:
Green access to alkenes using catalytic olefination reaction
Metathesis Portal. First reported in 1955 by Anderson et al. using a Ti(II) catalyst, for the polymerization of norbornene, the metathesis reaction gained interests and popularity over the last decade. Further investigations in the mechanism of the transformation by Chauvin sparked the development of novel more well-defined metathesis catalysts. Independently, Grubbs and Schrock reported novel functional-group tolerant catalysts. This breakthrough in olefin metathesis was rewarded in 2005 by a Nobel Prize to Chauvin, Grubbs, and Schrock for their contributions. The development of this technology over the years, brought to the forefront the use of Molybdenum, Ruthenium, and Tungsten as metals for metathesis.
Olefin metathesis - ScienceDirect
In the presence of a strong base such as pyridine, the reagent is functionally equivalent to "Cp2Ti=CH2".These Ti-based catalysts are not nearly as active or tolerant of carbonyl functionalities as the later catalysts, but has shown that these Ti complexes undergo stoichiometric Wittig-like reactions with ketones, aldehydes and other carbonyls to form the corresponding methylene derivatives.
C&EN: COVER STORY - OLEFIN METATHESIS: THE EARLY DAYS
For example when R = tert-butyl, the complex reacts only with strained cyclic olefins, making it an ideal .These catalysts have a high tolerance for functionality, although they are air and water-sensitive.