Diphosphine of formula I R1R2P—H2C—Ar—CH2PR1R2  (I) are prepared by a process that comprises a) reacting a dimethyl compound of formula II H3C—Ar—CH3  (II) with a base and an N-substituted aminophosphorous halide to form bis(aminophosphinomethyl) compound of the formula III R3R4P—H2C—Ar—CH2—PR3R4  (III) b) reacting the compound of formula III with HCl to form bis(dichlorophosphinomethyl) compound of formula IV Cl2P—H2C—Ar—CH2—PCl2  (IV) and c) reacting the compound of formula IV with an organometallic reagent to give the product compound of formula I, wherein groups R1 and R2 are each, independently of one another, a substituted or unsubstituted aromatic, heteroaromatic or aliphatic hydrocarbon group and may have a covalent bond connecting them and Ar is a substituted or unsubstituted aromatic or heteroaromatic hydrocarbon group an R3 and R4 are each, independently of one another, an N-substituted alkylamino or arylamino group.