Hydrogen Donors
A historically prominent transfer hydrogenation agent is diimide, which becomes oxidized to the very stable N2:
The diimide is generated from hydrazine. Two hydrocarbons that can serve as hydrogen donors are cyclohexene or cyclohexadiene. In this case an alkane is formed along with the formation of benzene. The driving force of the reaction being the gain of aromatic stabilization energy when benzene is formed. Pd can be used as a catalyst and a temperature of 100 °C is employed. One limitation of using transfer hydrogenation for the production of alkane is that it cannot be used to prepare methane as no unsaturated hydrocarbon contain only one carbon. More exotic transfer hydrogenations have been reported, including this intramolecular one:
Many reactions exist with alcohol as the hydrogen donor. Examples are the sodium metal mediated Birch reduction (arenes) and the Bouveault-Blanc reduction (esters). The combination of magnesium and methanol is used in alkene reductions, e.g. the synthesis of asenapine:
Read more about this topic: Transfer Hydrogenation
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