1,2-Diphenyl-1,2-ethylenediamine, DPEN, is an organic compound with the formula H<sub>2</sub>NCHPhCHPhNH<sub>2</sub>, where Ph is phenyl (C<sub>6</sub>H<sub>5</sub>). DPEN exists as three stereoisomers: meso and two enantiomers S,S- and R,R-. The chiral diastereomers are used in asymmetric hydrogenation. Both diastereomers are bidentate ligands.
1,2-Diphenyl-1,2-ethylenediamine can be prepared from benzil by reductive amination. DPEN can be obtained as both the chiral and meso diastereomers, depending on the relative stereochemistry of the two CHPhNH<sub>2</sub> subunits. The chiral diastereomer, which is of greater value, can be resolved into the R,R- and S,S- enantiomers using tartaric acid as the resolving agent. In methanol, the R,R enantiomer has a specific rotation of [ñ]<sub>23</sub> +106ñ1ð.
N-tosylated derivative, TsDPEN, is a ligand precursor for catalysts for asymmetric transfer hydrogenation. For example, (cymene)Ru(S,S-TsDPEN) catalyzes the hydrogenation of benzil into (R,R)-hydrobenzoin. In this reaction, formate serves as the source of H<sub>2</sub>:
This transformation is an example of desymmetrization, the symmetric molecule benzil is converted to the dissymmetric product.
DPEN is a key ingredients of Ryà Âji Noyori's 2nd generation ruthenium-based chiral hydration catalyst, for which he earned the Nobel Prize in Chemistry in 2001.