The invention relates to phosphacyclohexanes of general formulae I and II, wherein the following designations, among others, apply: R can represent hydrogen, C_1-100-alkyl, C_7-20-aralkyl, C_7-20-alkaryl, and C_6-12-aryl: R¹ to R¹⁰ can independently represent hydrogen, C_1-20-alkyl, C_7-20-aralkyl, C_7-20-alkaryl, and C_6-12-aryl: W, W can independently represent single bonds or bridges comprising 1 to 20 carbon atoms, which can form part of a cyclic or aromatic group and can be interrupted by heteroatoms. Said phosphacyclohexanes are used as ligands in transition metal complexes of transition metals belonging to groups VIII to X of the periodic table. ##STR1##