An investigation has been made of the liquid-phase hydrogenation of 1-heptyne on P-complexes of palladium(II) with 1,5,3,7-diazadiphosphocyclo-octanes and 1,3,5-diazaphosphosinanes in ethanol and benzene. The dependence of the activity and selectivity of the reaction on the substituents at the nitrogen atoms in the complex and on the solvent has been established.