Catalyst comprising a complex of a metal of subgroup VIII, on the basis of a phosphonite ligand and method for hydroformylation

A catalyst comprising at least one rhodium complex with a phosphonite ligand of formula I

• wherein
• R1 is a C3-C6-chain wherein the carbon atoms are connected through single bonds or through single bonds and from 1 to 3 double bonds, which chain is optionally fused with from 1 to 3 rings selected from the group consisting of aryl and hetaryl, wherein the rings are unsubstituted or carry from 1 to 3 substituents selected from the group consisting of alkyl, cycloalkyl, aryl, alkoxy, cycloalkyloxy, aryloxy, halogen, trifluoromethyl, nitro, cyano, carboxyl and NE1E2,
• E1 and E2 are identical or different and each is alkyl, cycloalkyl or aryl,
• m is 0 or 1, and
• the moieties
• and
• are identical or different and denote each a 5- to 8-membered heterocycle which is optionally fused with from 1 to 3 rings selected from the group consisting of cycloalkyl, aryl and hetaryl, wherein the rings are unsubstituted or carry from 1 to 3 substituents selected from the group consisting of alkyl, alkoxy, halogen, nitro, cyano and carboxyl,
• or a salt thereof.