Phosphane ligands of formula wherein X independently of Y represents a nitrogen atom or a C-R 2 group and Y independently of X represents a nitrogen atom or a C-R 9 group, R 1 for each of the two R 1 groups independently of the other represents a radical selected from the group C 1 -C 2 4-alkyl, C 3 -C 20 -cycloalkyl, which includes especially both monocyclic and also bi- and tri-cyclic cycloalkyl radicals, C 2 -C 13 -heteroaryl, wherein the number of hetero atoms, selected from the group N, O, S, may be from 1 to 2, wherein the two radicals R 1 may also be linked to one another, and wherein the above-mentioned radicals R 1 may themselves each be mono- or poly-substituted independently of one another by substituents selected from the group hydrogen, C 1 -C 20 -alkyl, C 2 -C 20 -alkenyl, C 3 -C 8 -cycloalkyl, C 2 -C 9 -heteroalkyl, C 5 -C 10 -aryl, C 2 -C 9 -heteroaryl, wherein the number of hetero atoms from the group N, O, S may be from 1 to 4, C 1 -C 20 -alkoxy, C 1 -C 10 -haloalkyl, hydroxy, amino of the forms NH-(C 1 -C 20 -alkyl), NH-(C 5 -C 10 -aryl), N (C 1 -C 20 -alkyl) 2, N(C 1 -C 20 -alkyl) (C 5 -C 10 -aryl), N(C 5 -C 10 -aryl) 2, N(C 1 -C 20 -alkyl/C 5 -C 10 -aryl 3) 3 +, NH-CO-C 1 -C 20 -alkyl, NH-CO-C 5 -C 10 -aryl, carboxylato of the forms COOH and COOQ (wherein Q represents either a monovalent cation or C 1 -C 8 -alkyl), C 1 -C 6 -acyloxy, sulfinato, sulfonato of the forms SO 3 H and SO 3 Q (wherein Q represents either a monovalent cation, C 1 -C 20 -alkyl or C 5 -C 10 -aryl), tri-C 1 -C 6 -alkylsilyl, wherein two of the mentioned substituents may also be bridged with one another, R 2 -R 9 represent a hydrogen, alkyl, alkenyl, cycloalkyl, aromatic or heteroaromatic aryl, O-alkyl, NH-alkyl, N-(alkyl) 2, O-(aryl), NH-(aryl), N-(alkyl)(aryl), O-CO-alkyl, O-CO-aryl, F, Si(alkyl) 3, CF 3, CN, CO 2 H COH, SO 3 H, CONH 2, CONH(alkyl), CON(alkyl) 2, SO 2 (alkyl), SO(alkyl), SO(aryl), SO 2 (aryl), SO 3 (alkyl), SO 3 (aryl), S-alkyl, S-aryl, NH-CO(alkyl), CO 2 (alkyl), CONH 2, CO(alkyl), NHCOH, NHCO 2 (alkyl), CO(aryl), CO 2 (aryl) radical, wherein two or more adjacent radicals, each independently of the other(s), may also be linked to one another so that a condensed ring system is present and wherein in R 2 to R 9 alkyl represents a hydrocarbon radical having from 1 to 20 carbon atoms which may in each case be linear or branched, alkenyl represents a mono- or polyunsaturated hydrocarbon radical having from 2 to 20 carbon atoms which may in each case be linear or branched, cycloalkyl represents a hydrocarbon having from 3 to 20 carbon atoms, aryl represents a 5- to 14-membered aromatic radical, wherein from one to four carbon atoms in the aryl radical may also be replaced by hetero atoms from the group nitrogen, oxygen and sulfur so that a 5- to 14-membered heteroaromatic radical is present, wherein the radicals R 2 to R 9 may also carry further substituents as defined for R 1. X independently of Y represents a nitrogen atom or a C-R 2 group and Y independently of X represents a nitrogen atom or a C-R 9 group, R 1 for each of the two R 1 groups independently of the other represents a radical selected from the group C 1 -C 2 4-alkyl, C 3 -C 20 -cycloalkyl, which includes especially both monocyclic and also bi- and tri-cyclic cycloalkyl radicals, C 2 -C 13 -heteroaryl, wherein the number of hetero atoms, selected from the group N, O, S, may be from 1 to 2, wherein the two radicals R 1 may also be linked to one another, and wherein the above-mentioned radicals R 1 may themselves each be mono- or poly-substituted independently of one another by substituents selected from the group hydrogen, C 1 -C 20 -alkyl, C 2 -C 20 -alkenyl, C 3 -C 8 -cycloalkyl, C 2 -C 9 -heteroalkyl, C 5 -C 10 -aryl, C 2 -C 9 -heteroaryl, wherein the number of hetero atoms from the group N, O, S may be from 1 to 4, C 1 -C 20 -alkoxy, C 1 -C 10 -haloalkyl, hydroxy, amino of the forms NH-(C 1 -C 20 -alkyl), NH-(C 5 -C 10 -aryl), N (C 1 -C 20 -alkyl) 2, N(C 1 -C 20 -alkyl) (C 5 -C 10 -aryl), N(C 5 -C 10 -aryl) 2, N(C 1 -C 20 -alkyl/C 5 -C 10 -aryl 3) 3 +, NH-CO-C 1 -C 20 -alkyl, NH-CO-C 5 -C 10 -aryl, carboxylato of the forms COOH and COOQ (wherein Q represents either a monovalent cation or C 1 -C 8 -alkyl), C 1 -C 6 -acyloxy, sulfinato, sulfonato of the forms SO 3 H and SO 3 Q (wherein Q represents either a monovalent cation, C 1 -C 20 -alkyl or C 5 -C 10 -aryl), tri-C 1 -C 6 -alkylsilyl, wherein two of the mentioned substituents may also be bridged with one another, R 2 -R 9 represent a hydrogen, alkyl, alkenyl, cycloalkyl, aromatic or heteroaromatic aryl, O-alkyl, NH-alkyl, N-(alkyl) 2, O-(aryl), NH-(aryl), N-(alkyl)(aryl), O-CO-alkyl, O-CO-aryl, F, Si(alkyl) 3, CF 3, CN, CO 2 H COH, SO 3 H, CONH 2, CONH(alkyl), CON(alkyl) 2, SO 2 (alkyl), SO(alkyl), SO(aryl), SO 2 (aryl), SO 3 (alkyl), SO 3 (aryl), S-alkyl, S-aryl, NH-CO(alkyl), CO 2 (alkyl), CONH 2, CO(alkyl), NHCOH, NHCO 2 (alkyl), CO(aryl), CO 2 (aryl) radical, wherein two or more adjacent radicals, each independently of the other(s), may also be linked to one another so that a condensed ring system is present and