1,3-Bis(diphenylphosphino)propane

1,3-Bis(diphenylphosphino)propane (dppp) is an organophosphorus compound with the formula Ph$2$P(CH$2$)$3$PPh$2$. The compound is a white solid that is soluble in organic solvents. It is slightly air-sensitive, degrading in air to the phosphine oxide. It is classified as a diphosphine ligand in coordination chemistry and homogeneous catalysis.

The diphosphine can be prepared by the reaction of lithium diphenylphosphide and 1,3-dichloropropane (Ph = C$6$H$5$):
 * 2 Ph$2$PLi + Cl(CH$2$)$3$Cl   →   Ph$2$P(CH$2$)$3$PPh$2$  +  2 LiCl

However, it can be synthesised via a much more controllable (and cheaper) route, via metal-halogen exchange and then metathesis:
 * Br(CH$2$)$3$Br + 2 $t$BuLi → Li(CH$2$)$3$Li + 2 $t$BuBr
 * Li(CH$2$)$3$Li + 2 PCl$3$ → Cl$2$P(CH$2$)$3$PCl$2$ + 2 LiCl
 * Cl$2$P(CH$2$)$3$PCl$2$ + 4 PhLi → Ph$2$P(CH$2$)$3$PPh$2$ + 4 LiCl

Coordination chemistry and use as co-catalyst
The diphosphine serves as a bidentate ligand forming six-membered C$3$P$2$M chelate ring with a natural bite angle of 91°. For example, the complex dichloro(1,3-bis(diphenylphosphino)propane)nickel is prepared by combining equimolar portions of the ligand and nickel(II) chloride hexahydrate. This nickel complex serves as a catalyst for the Kumada coupling reaction. Dppp is also used as a ligand for palladium(II) catalysts to co-polymerize carbon monoxide and ethylene to give polyketones. Dppp can sometimes be used in palladium-catalyzed arylation under Heck reaction conditions to control regioselectivity.