Phosphabenzene compounds of the formula (I) where the radicals R1 to R13 are, independently of one another, hydrogen, COOM, SO3M, NR3X, NR2, OR, COOR or SR (where M=hydrogen, NH4 or alkali metal, X=anion, R=hydrogen or C1-C6-alkyl), or C1-C12-alkyl, C6-C12-aryl, C7-C12-aralkyl, C7-C12-alkaryl or C3-C6-heteroaromatics, where the alkyl, aryl, alkaryl and aralkyl radicals may bear the abovementioned radicals as substituents and two or more of the radicals may be joined to form aliphatic or fused-on rings, where at least one of the radicals R4 and R8 and at least one of the radicals R9 and R13 is not hydrogen, can be used for preparing hydroformylation catalysts.