C&EN: COVER STORY - OLEFIN METATHESIS: THE EARLY DAYS
The paper analyzes the kinetics of olefin metathesis and addresses whether the reaction of a cyclic alkene with an acyclic alkene should give three products or just one.
23/12/2002 · OLEFIN METATHESIS: THE EARLY DAYS ..
Olefin metathesis involves the exchange of two alkylidene groups to generate two new olefins from one or more starting alkenes. Cleavage of the carbon-carbon double bond is accompanied by the formation of two new carbon-carbon double bonds. This reaction was first observed in 1931, investigated by Du Pont and other manufacturers in the 1950's, and finally defined by Calderon in 1967. Partly due to its relevance to petrochemical industry, olefin metathesis reactions have been investigated extensively. Four general classes of reactions have emerged: cross metathesis, an intermolecular reaction of two alkenes; ring-opening metathesis polymerization (ROMP), in which a cyclic alkene opens to form a polyolefin; ring-opening metathesis (ROM), the opening of a cyclic alkene to form a diene; and ring-closing metathesis (RCM), in which reaction of a diene affords a cyclic alkene and a small olefinic byproduct. RCM is the focus of this article (Eq. 1).
However, metathesis can occur between any two olefins and/or dienes as long as there is a pair of double bonds.
The equilibrium metathesis reactions for the C4 fraction are shown in Table 1.
Formation of tetrasubstituted C-C double bonds via …
Phosphonates containing two or more double bonds cyclize in the presence of catalyst 2. The vinyl group reacts preferentially to form a five- rather than a seven-membered ring (Eq. 14).
Olefin Metathesis Polymerization - pslc
Unsaturated lactams are a biochemically important class of heterocycles that can be prepared via ring-closing metathesis. Catalyst 1 is effective in the preparation of five- or six-membered lactams, but crotonamides must be used as unsubstituted α,β-unsaturated amides coordinate to molybdenum, preventing reaction (Eq. 16).
Ring-closing metathesis - Organic Reactions Wiki
The first was from Ernst Otto Fischer at the University of Munich, Germany, about a new type of metal-carbon bond exemplified in the metal carbene (methylmethoxycarbene)pentacarbonyl tungsten--(CO)5W=C(CH3)(OCH3) [
Catalytic Double-Bond Metathesis without the Transition Metal
In the operating system with ethylene (ie, conventional metathesis), if there is 1-butene present the catalyst system typically employs a co-catalyst that provides double bond isomerisation activity.
depending on which double bond of the diene system is ..
Unsubstituted α,β-unsaturated esters can likewise coordinate to the metal center and prevent reaction. Including a Lewis acid such as titanium(IV) isopropoxide in the reaction mixture does not interfere with metathesis and prevents coordination to the catalytic metal, enabling reactions of acrylates (Eq. 17).
long as there is a pair of double bonds
While it is commonly believed that ethylene is required for the metathesis reaction and that isobutylene should be minimised, this is not correct.