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Alkene Reactions: Alkene Hydrogenation using H2 and Pd, Pt, or Ni

Metal catalysts such as palladium (Pd), platinum (Pt), or nickel (Ni) can be combined with hydrogen (H2) to react with alkenes to form alkanes:

Alkene Reactions: Alkene Hydrogenation using H2 and Pd, Pt, or Ni image3.png

The H2 and alkene are adsorbed onto the surface of the metal catalyst. This is not to say that bonding occurs but instead the H2 and alkene meet together on the surface of the metals and the reaction proceeds. The 2 hydrogen atoms that are added are added in syn fashion. In the example shown below, the red carbon will have stereochemistry after the reaction has occurred while the blue carbon will not due to the presence of 2 hydrogens on the blue carbon:

Syn Addition

Alkene Reactions: Alkene Hydrogenation using H2 and Pd, Pt, or Ni image1.png

No stereocenters

Alkene Reactions: Alkene Hydrogenation using H2 and Pd, Pt, or Ni image4.png

The reaction mechanism is depicted below:

Alkene Reactions: Alkene Hydrogenation using H2 and Pd, Pt, or Ni image2.png

In the first step, the H2 and alkene adsorb to the platinum, which catalyzes the reaction.

In the second step, the alkene bond is able to react with H2, resulting in a syn addition of hydrogen to each carbon atom and the dissolution of the double bond.

The reagent used for this reaction is H2 with a metal catalyst such as Pt, Pd, Ni, or Rh.