Bis(diphenylphosphino)methane
# Bis(diphenylphosphino)methane

1,1-Bis(diphenylphosphino)methane (dppm), is an organophosphorus compound with the formula $CH_2(PPh_2)_2.$ Dppm, a white, crystalline powder, is used in inorganic and organometallic chemistry as a ligand. It is more specifically a chelating ligand because it is a ligand that can bond to metals with two phosphorus donor atoms. The natural bite angle is 73°.

## Synthesis and reactivity

1,1-Bis(diphenylphosphino)methane was first prepared by the reaction of sodium diphenylphosphide $(Ph_2PNa)$ with dichloromethane:

    $Ph_3P$ + 2 Na → $Ph_2PNa$ + NaPh
    $2NaPPh_2$ + $CH_2Cl_2$ → $Ph_2PCH_2PPh_2$ + 2 NaCl

The methylene group $(CH_2)$ in dppm (and especially its complexes) is mildly acidic. The ligand can be oxidized to give the corresponding oxides and sulfides $CH_2[P(E)Ph_2]_2$ (E = O, S). The methylene group is even more acidic in these derivatives.

## Coordination chemistry

As a chelating ligand, 1,1-bis(diphenylphosphino)methane forms a four-membered ring with the constituents $MP_2C.$ The ligand promotes the formation of bimetallic complexes that feature five-membered $M_2P_2C$ rings. In this way, dppm promotes the formation of bimetallic complexes. One such example is the dipalladium chloride, $Pd_2Cl_2(dppm)_2.$ In this complex, the oxidation state for the Pd centres are I. Bis(diphenylphosphino)methane gives rise to a family of coordination compounds known as A-frame complexes.

