Process for preparing diphosphines

A process for preparing diphosphines of the formula I

• R1R2P—H2C—Ar—CH2PR1R2 (I)
• which comprises
• a) reacting dimethyl compounds of the formula II,
• H3C—Ar—CH3 (II)
• with a base and an N-substituted aminophosphorus halide to form bis(aminophosphinomethyl) compounds of the formula III
• R3R4P—H2C—Ar—CH2—PR3R4 (III)
• b) reacting the compounds of the formula III obtained in this way with HCl to form bis(dichlorophosphinomethyl) compounds of the formula IV
• Cl2P—H2C—Ar—CH2—PCl2 (IV)
• and c) reacting the compounds of the formula IV obtained in this way with organometallic reagents to give the target compounds of the formula I, where R1 and R2 are each, independently of one another, a substituted or unsubstituted aromatic, heteroaromatic or aliphatic hydrocarbon radical and may have a covalent bond connecting them and Ar is a substituted or unsubstituted aromatic or heteroaromatic hydrocarbon radical and R3 and R4 are each, independently of one another, an N-substituted alkylamino or arylamino radical.