Hydrovinylation
In organic chemistry, hydrovinylation is the formal insertion of an alkene into the C-H bond of ethylene (Template:Chem2):
The more general reaction, hydroalkenylation, is the formal insertion of an alkene into the C-H bond of any terminal alkene. The reaction is catalyzed by metal complexes. A representative reaction is the conversion of styrene and ethylene to 3-phenybutene:[1]
Ethylene dimerization
The dimerization of ethylene which gives 1-butene is another example of a hydrovinylation. In the Dimersol and Alphabutol Processes, alkenes are dimerized for the production of gasoline and for comonomers such as 1-butene. These processes operate at several refineries across the world at the scales of about 400,000 tons/year (2006 report).[2] 1-Butene is amenable to isomerization to 2-butenes, which is used in olefin conversion technology to give propylene.
In organic synthesis
The addition can be done highly regio- and stereoselectively, although the choices of metal, ligands, and counterions often play very important role. Many metals have also been demonstrated to form active catalysts, including nickel[3][4][5] and cobalt.[6][7][8]
In a stoichiometric version of a hydrovinylation reaction, nucleophiles add to an electrophilic transition metal alkene complex, forming a C-C bond. The resulting metal alkyl undergoes beta-hydride elimination, liberating the vinylated product.[9]
Hydroarylation
Hydroarylation is again a special case of hydrovinylation. Hydroarylation has been demonstrated for alkyne and alkene substrates. An early example was provided by the Murai reaction, which involves the insertion of alkenes into a C-H bond of acetophenone. The keto group directs the regiochemistry, stabilizing an aryl intermediate.[10]
When catalyzed by palladium carboxylates, a key step is electrophilic aromatic substitution to give a Pd(II) aryl intermediate.[11] Gold behaves similarly.[12] Hydropyridination is a similar reaction, but entails addition of a pyridyl-H bond to alkenes and alkynes.[13]
See also
- Vinylation, the process of affixing a vinyl group
References
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