The invention relates to the preparation and use as catalysts of diphosphines of the formula (I)
1
in which
R is C
6
-C
14
-aryl or C
4
-C
13
-heteroaryl containing 1 to 3 heteroatoms selected from the group consisting of nitrogen, oxygen, and sulfur, wherein the aryl and heteroaryl radicals may optionally be substituted by halogen, C
1
-C
6
-alkyl, C
1
-C
6
-alkoxy, and/or trimethylsilyl, and
R
1
to R
4
, independently of one another, are each hydrogen, C
1
-C
10
-alkyl, C
1
-C
10
-alkoxy, F, Cl, or Br.