1,1-Bismethane (dppm), is an organophosphorus compound with the formula CH2(PPh2)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 is attached to the central metals (the phosphorus) by bonds from two or more donor atoms.

Synthesis and reactivity

1,1-Bis(diphenylphosphino)methane was first prepared by the reaction of sodium diphenylphosphide (Ph2PNa) with dichloromethane:
Ph3P + 2 Na → Ph2PNa + NaPh
2NaPPh2 + CH2Cl2 → Ph2PCH2PPh2 + 2 NaCl

The methylene group (CH2) in dppm (and especially its complexes) are mildly acidic. The ligand can be oxidized to give the corresponding oxides and sulfides CH2[P(E)Ph2]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 MP2C. The ligand promotes the formation of bimetallic complexes that feature five-membered M2P2C rings. In this way, dppm promotes the formation of bimetallic complexes. One such example is the dipalladium chloride, Pd2Cl2(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 complex
A-frame complex
A-frame complexes are coordination compounds that contain two bridging bidentate ligands and a single atom bridge. They have the formula M22L2, where bd is a bidental ligand like dppm, and X and L are a wide variety of ligands...

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