Hydrovinylation

In organic chemistry, hydrovinylation is the formal insertion of an alkene into the C-H bond of ethylene (H₂C=CH₂):

CH₂=CHR + CH₂=CH₂ → CH₃−CHR−CH=CH₂

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:

$\mathrm{P}\mathrm{h}\mathrm{C}\mathrm{H}=\mathrm{C}\mathrm{H}{\phantom{A}}_2+\mathrm{C}\mathrm{H}{\phantom{A}}_2=\mathrm{C}\mathrm{H}{\phantom{A}}_2⟶\mathrm{H}-\mathrm{C}\mathrm{H}{\phantom{A}}_2-\mathrm{C}\mathrm{H}(\mathrm{P}\mathrm{h})-\mathrm{C}\mathrm{H}=\mathrm{C}\mathrm{H}{\phantom{A}}_2$

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). 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 and cobalt.

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.

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.

File:Figure 1. General scheme of a Murai reaction.png

A Murai reaction (X = directing group, typically X = O).

When catalyzed by palladium carboxylates, a key step is electrophilic aromatic substitution to give a Pd(II) aryl intermediate. Gold behaves similarly. Hydropyridination is a similar reaction, but entails addition of a pyridyl-H bond to alkenes and alkynes.

See also

• Vinylation, the process of affixing a vinyl group