Diphenylethylenediamine
# Diphenylethylenediamine

1,2-Diphenyl-1,2-ethylenediamine, DPEN, is an organic compound with the formula $H_2NCHPhCHPhNH_2,$ where Ph is phenyl $(C_6H_5).$ 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.

## Preparation and optical resolution

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 $CHPhNH_2$ 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 $[α]_{23}$ +106±1°.

## Asymmetric catalysis

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 $H_2:$

    PhC(O)C(O)Ph + 2 $H_2$ → PhCH(OH)CH(OH)Ph (R,R isomer)

This transformation is an example of desymmetrization, the symmetric molecule benzil is converted to the dissymmetric product.

DPEN is a key ingredients of Ryōji Noyori's 2nd generation ruthenium-based chiral hydration catalyst, for which he earned the Nobel Prize in Chemistry in 2001.

