1,2-Bis(diphenylphosphino)ethane

1,2-Bis(diphenylphosphino)ethane (dppe) is an organophosphorus compound with the formula (Ph$26$PCH$24$)$2$ (Ph = phenyl). It is a common symmetrical bidentate ligand in coordination chemistry. It is a white solid that is soluble in organic solvents.

Preparation
The preparation of dppe entails the alkylation of NaP(C6H5)2 with 1,2-dichloroethane:
 * 2 NaP(C6H5)2 + ClCH2CH2Cl  ->  (C6H5)2PCH2CH2P(C6H5)2  +  2 NaCl

Reactions
The reduction of dppe by lithium give the disecondary phosphine:
 * (C6H5)2PCH2CH2P(C6H5)2 4 Li ->  Li(C6H5)PCH2CH2P(C6H5)Li  +  2 C6H5Li

Hydrolysis gives the bis(secondary phosphine).
 * Li(C6H5)PCH2CH2P(C6H5)Li + 2 H2O -> H(C6H5)PCH2CH2P(C6H5)H  +  2 LiOH
 * [[Image:HFeCl dppe 2.svg|thumb|left|The bis(dppe) complex [[Chlorobis(dppe)iron hydride|HFeCl(dppe)$2$]] is one of the most accessible transition metal hydrides.]]

Treatment of dppe with hydrogen peroxide pproduces the phosphine oxides (C6H5)2P(O)CH2CH2P(C6H5)2 and (C6H5)2P(O)CH2CH2P(O)(C6H5)2. Selective mono-oxidation of dppe can be achieved by benzylation followed by hydrolysis:
 * (C6H5)2PCH2CH2P(C6H5)2 + C6H5CH2Br -> (C6H5)2PCH2CH2P(C6H5)2(CH2C6H5)]Br
 * (C6H5)2PCH2CH2P(C6H5)2(CH2C6H5)]Br + NaOH ->  (C6H5)2PCH2CH2P(O)(C6H5)2  + C6H5CH3  +  NaBr

Hydrogenation of dppe gives the ligand bis(dicyclohexylphosphino)ethane.

Coordination complexes
Many coordination complexes of dppe are known, and some are used as homogeneous catalysts. Dppe is almost invariably chelating, although there are examples of monodentate (e.g., W(CO)$2$(dppe)) and of bridging behavior. The natural bite angle is 86°.

Related compounds

 * 1,2-Bis(dimethylphosphino)ethane
 * Bis(diphenylphosphino)methane