The novel diamine(dppp)ruthenium(II) complexes 3L1–3L12 have been obtained by reaction of equimolar amounts of Cl2Ru(dppp)2 (2) with the diamines L1–L12 in excellent yields. Within a few minutes one of the diphosphine ligands was quantitatively exchanged by the corresponding diamine. X-ray structural investigations of 3L1, 3L2, and 3L8 show triclinic unit cells with the space groups P (3L1, 3L2) and P 1 (3L8). Whereas in solution all these complexes prefer a trans-RuCl2 configuration, in the solid state cis-(3L1, 3L2) and trans-isomers (3L8) were observed. With the exception of 3L5, 3L6, and 3L12 all mentioned ruthenium complexes are highly catalytically active in the hydrogenation of the α,β-unsaturated ketone trans-4-phenyl-3-butene-2-one. In most cases the conversions and selectivities toward the formation of the unsaturated alcohol trans-4-phenyl-3-butene-2-ol were >99% with high turnover frequencies (TOFs) under mild conditions.