The invention relates to phosphacyclohexanes of general formulae I and II, wherein the following designations, among others, apply: R can represent hydrogen, C1-100-alkyl, C7-20-aralkyl, C7-20-alkaryl, and C6-12-aryl: R1 to R10 can independently represent hydrogen, C1-20-alkyl, C7-20-aralkyl, C7-20-alkaryl, and C6-12-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.