Abstract: A hydrogenation catalyst comprising (A) a transition metal compound in which a group having a heterocyclic skeleton is bonded to Ti, Zr or Hf through an oxygen atom or a nitrogen atom, a representative of which compound is bis(cyclopentadienyl)titanium bis(tetrahydrofurfuryloxy) and (B) an organic compound, halide or hydride of a metal of Groups I to III of the Periodic Table or comprising the constituent (A), the constituent (B) and (C) a polar, organic compound such as an alcohol, a carboxylic acid or the like. An olefinically unsaturated compound can be hydrogenated with a high efficiency by contacting the compound with hydrogen in the presence of the above catalyst in an inert, organic solvent. The above catalyst has a very high catalytic activity, is excellent in hydrogenation selectivity and thermal resistance, also excellent in storage stability and maintainability of catalytic activity and is hardly affected by the co-existing impurities.

Abstract: A catalyst composition comprising: (a) a bis(cyclopentadienyl) transition metal compound, (b) at least one polarized compound selected from the group consisting of carbonyl group-containing compounds and epoxy group containing compounds, and (c) an organic lithium compound. It has a high hydrogenation activity and is useful for hydrogenating olefinically unsaturated polymers for providing the olefinically unsaturated polymers with excellent characteristics as superior weatherability, good heat resistance, superb oxidation resistance, and the like.