is the preferred solvent the mole ratio of the catalyst component to each other is important in obtaining the improved hydrogenation rates when one hydrogenates cyclopentadiene to form cyclopentene the mole ratio of the trialkylaluminum compound or organolithium to the soluble nickel compound must be within a range of from 7 1 to 11 1 to obtain improved hydrogenation rates over those disclosed in german pat no 2 327 230 as noted in the german patent the mole ratio of the pyridine to the nickel compound should be within the range of 1 1 to 2 5 1 with a more preferred ratio of about 2 1 the practice of this invention is further illustrated by reference to the following examples which are intended to be representative rather than restrictive of the scope of the invention unless otherwise indicated all parts and percentages are by weight a typical procedure of the practice of the invention is employed wherein 1 3 millimoles mm of pyridine as a one molar solution in toluene are added to 0 65 mm of nickel octanoate as a 0 1 molar solution in toluene under nitrogen after mixing these two materials for about 5 minutes 4 55 mm of triethylaluminum as a two molar solution in toluene are added under nitrogen and the mixture stirred for at least two.