Dimeric bisacylphosphines, oxides and sulfides

A compound of the formula I ##STR46## in which Z is oxygen or sulfur,

• n and m are independently of one another 0 or 1,
• R.sub.1, R.sub.2, R.sub.3 and R.sub.4 independently of one another are C.sub.1 -C.sub.20 alkyl, cyclopropyl, cyclopentyl, cyclohexyl, C.sub.2 -C.sub.8 alkenyl, phenyl which is unsubstituted or is substituted one to four times by C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.12 alkoxy, C.sub.1 -C.sub.6 alkylthio and/or halogen, naphthyl which is unsubstituted or is substituted one to four times by C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.12 alkoxy, C.sub.1 -C.sub.6 alkylthio and/or halogen, biphenyl which is unsubstituted or is substituted one to four times by C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.12 alkoxy, C.sub.1 -C.sub.6 alkylthio and/or halogen, or R.sub.1, R.sub.2, R.sub.3 and R.sub.4 independently of one another are a 5- or 6-membered heterocyclic ring which contains O, S or N, or R.sub.1 and R.sub.2 or/and R.sub.3 and R.sub.4 are linked to form a ring containing 4 to 10 carbon atoms which is unsubstituted or is substituted by 1 to 6 C.sub.1 -C.sub.4 alkyl groups,
• X is linear or branched C.sub.1 -C.sub.18 alkylene, is C.sub.2 -C.sub.18 alkylene which is interrupted one or more times by --O--, --S--, --NR.sub.5 --, --P(O)R.sub.6 -- or --SO.sub.2 --, or is C.sub.1 -C.sub.6 alkylene which is substituted by Cl, F, C.sub.1 -C.sub.4 alkoxy, COOR.sub.7, phenyl, C.sub.1 -C.sub.4 alkylphenyl, C.sub.1 -C.sub.4 alkylnaphthyl, phenyl-C.sub.1 -C.sub.4 alkyl, naphthyl-C.sub.1 -C.sub.4 alkyl, phenyl-C.sub.1 -C.sub.4 alkoxy, naphthyl-C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkoxy-C.sub.1 -C.sub.4 alkoxy and/or CN, or X is C.sub.2 -C.sub.8 alkylene which is substituted by one or two groups of the formula G ##STR47## or X is a group of the formula (II), ##STR48## in which a and b independently of one another are 0 or 1,
• the sum of d and f is 3 to 8, with neither d nor f being 0,
• or X is a group --CH.sub.2 --CH.dbd.CH--CH.sub.2 -- or --CH.sub.2 --C.tbd.C--CH.sub.2 --, or X is xylylene, ##STR49## or X is a group of the formula (XII), or (XIV), ##STR50## ##STR51## in which Z and G are as defined above and
• Y is a single bond, --CR.sub.8 R.sub.9 --, --O--, --NR.sub.5 --, --S--, --SO.sub.2 --, --(CH.sub.2).sub.p -- or --CH.dbd.CH--,
• p is a number from 2 to 12,
• R.sub.5 is hydrogen, C.sub.1 -C.sub.12 alkyl or phenyl,
• R.sub.6 is C.sub.1 -C.sub.4 alkyl or phenyl,
• R.sub.7 is C.sub.1 -C.sub.12 alkyl, C.sub.2 -C.sub.18 alkyl which is interrupted by one or more O atoms, or is benzyl, phenyl, cyclopentyl or cyclohexyl, and
• R.sub.8 is hydrogen, methyl or ethyl,
• R.sub.9 is hydrogen or C.sub.1 C.sub.4 alkyl, and
• R.sub.10 is hydrogen C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy or halogen.