The invention relates to a compound of formula (I)

##STR00001## where R.sup.1 and R.sup.3 are each a heteroaryl radical having five ring atoms, R.sup.2 and R.sup.4 are each independently selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, (C.sub.6-C.sub.20)-aryl; R.sup.1 and R.sup.3 may each independently be substituted by one or more substituents selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl-(C.sub.6-C.sub.20)-aryl, O(C.sub.3-C.sub.12)-cycloalkyl, S(C.sub.1-C.sub.12)-alkyl, S(C.sub.3-C.sub.12)-cycloalkyl, COO(C.sub.1-C.sub.12)-alkyl, COO(C.sub.3-C.sub.12)-cycloalkyl, CONH(C.sub.1-C.sub.12)-alkyl, CONH(C.sub.3-C.sub.12)-cycloalkyl, CO(C.sub.1-C.sub.12)-alkyl, CO(C.sub.3-C.sub.12)-cycloalkyl, N[(C.sub.1-C.sub.12)-alkyl].sub.2, (C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.6-C.sub.20)-aryl-O(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl, (C.sub.3-C.sub.20)-heteroaryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl-O(C.sub.1-C.sub.12)-alkyl, COOH, OH, SO.sub.3H, NH.sub.2, halogen; and R.sup.2 and R.sup.4, if they are (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl or (C.sub.6-C.sub.20)-aryl, may each independently be substituted by one or more substituents selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl-(C.sub.6-C.sub.20)-aryl, O(C.sub.3-C.sub.12)-cycloalkyl, S(C.sub.1-C.sub.12)-alkyl, S(C.sub.3-C.sub.12)-cycloalkyl, COO(C.sub.1-C.sub.12)-alkyl, COO(C.sub.3-C.sub.12)-cycloalkyl, CONH(C.sub.1-C.sub.12)-alkyl, CONH(C.sub.3-C.sub.12)-cycloalkyl, CO(C.sub.1-C.sub.12)-alkyl, CO(C.sub.3-C.sub.12)-cycloalkyl, N[(C.sub.1-C.sub.12)-alkyl].sub.2, (C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.6-C.sub.20)-aryl-O(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl, (C.sub.3-C.sub.20)-heteroaryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl-O(C.sub.1-C.sub.12)-alkyl, COOH, OH, SO.sub.3H, NH.sub.2, halogen; excluding the compounds of the formulae (1) and (2)

##STR00002##

The invention further relates to precursors for preparation of the compound according to the invention, to Pd complexes comprising the compound according to the invention and to the use thereof in alkoxycarbonylation.

The invention relates to a compound of formula (I)

##STR00001## where R.sup.1, R.sup.2, R.sup.3, R.sup.4 are each independently selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, (C.sub.6-C.sub.20)-aryl, (C.sub.3-C.sub.20)-heteroaryl; at least one of the R.sup.1, R.sup.2, R.sup.3, R.sup.4 radicals is a (C.sub.6-C.sub.20)-heteroaryl radical having at least six ring atoms; and R.sup.1, R.sup.2, R.sup.3, R.sup.4, if they are (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, (C.sub.6-C.sub.20)-aryl, (C.sub.3-C.sub.20)-heteroaryl or (C.sub.6-C.sub.20)-heteroaryl, may each independently be substituted by one or more substituents selected from (C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.12)-cycloalkyl, (C.sub.3-C.sub.12)-heterocycloalkyl, O(C.sub.1-C.sub.12)-alkyl, O(C.sub.1-C.sub.12)-alkyl-(C.sub.6-C.sub.20)-aryl, O(C.sub.3-C.sub.12)-cycloalkyl, S(C.sub.1-C.sub.12)-alkyl, S(C.sub.3-C.sub.12)-cycloalkyl, COO(C.sub.1-C.sub.12)-alkyl, COO(C.sub.3-C.sub.12)-cycloalkyl, CONH(C.sub.1-C.sub.12)-alkyl, CONH(C.sub.3-C.sub.12)-cycloalkyl, CO(C.sub.1-C.sub.12)-alkyl, CO(C.sub.3-C.sub.12)-cycloalkyl, N[(C.sub.1-C.sub.12)-alkyl].sub.2, (C.sub.6-C.sub.20)-aryl, (C.sub.6-C.sub.20)-aryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.6-C.sub.20)-aryl-O(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl, (C.sub.3-C.sub.20)-heteroaryl-(C.sub.1-C.sub.12)-alkyl, (C.sub.3-C.sub.20)-heteroaryl-O(C.sub.1-C.sub.12)-alkyl, COOH, OH, SO.sub.3H, NH.sub.2, halogen.

The invention further relates to precursors for preparation of the compound according to the invention, to Pd complexes comprising the compound according to the invention and to the use thereof in alkoxycarbonylation.

Alkoxylation reactions are performed in the presence of a phosphonium catalyst having the structure P.sup.+(XR.sup.1R.sup.2R.sup.3)A.sup.1 wherein R.sup.1 is a group having an unsubstituted or inertly substituted aromatic five-member ring having a direct bond between an atom of the aromatic five-member ring and the phosphorus atom, and each R.sup.2 is independently a group having an unsubstituted or inertly substituted, optionally heteroatomic, aromatic five- or six-member ring having a direct bond between a carbon atom of the optionally heteroatomic aromatic five- or six-member ring and the phosphorus atom. X is selected from fluorine, chlorine, bromine, iodine, C.sub.1-12 perfluoroalkyl, C.sub.1-12 alkyl, aryloxy and C.sub.1-12 alkoxy, and A is a weakly coordinating anion.