1,2-Bis(diphenylphosphino)ethane

1,2-Bis(diphenylphosphino)ethane (dppe) is an organophosphorus compound with the formula (Ph_2PCH_2)_2 (Ph = phenyl). It is a commonly used bidentate ligand in coordination chemistry. It is a white solid that is soluble in organic solvents. The preparation of dppe is by the alkylation of NaPPh_2: P(C_6H_5)_3 + 2 Na → NaP(C_6H_5)_2 + NaC_6H_5 NaP(C_6H_5)_2, which is readily air-oxidized, is treated with 1,2-dichloroethane (ClCH_2CH_2Cl) to give dppe: 2 NaP(C_6H_5)_2 + ClCH_2CH_2Cl → (C_6H_5)_2PCH_2CH_2P(C_6H_5)_2 + 2 NaCl The reduction of dppe by lithium to give PhHP(CH_2)_2PHPh has been reported. Ph_2P(CH_2)_2PPh_2 + 4 Li → PhLiP(CH_2)_2PLiPh + 2 PhLi Hydrolysis gives the bis(secondary phosphine): PhLiP(CH_2)_2PLiPh + 2 PhLi + 4H_2O → PhHP(CH_2)_2PHPh + 4 LiOH + 2 C_6H_6 Treatment of dppe with conventional oxidants such as hydrogen peroxide (H_2O_2), aqueous bromine (Br_2), etc., produces dppeO in low yield (e.g., 13%) as a result of non-selective oxidation. Selective mono-oxidation of dppe can be achieved by reaction with PhCH_2Br to give dppeO. Hydrogenation of dppe gives the ligand bis(dicyclohexylphosphino)ethane. 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)_5(dppe)) and of bridging behavior. The natural bite angle is 86°.