Abstract: The processability of a polybutadiene with a high content of 1,4-cis-structure is improved by means of the addition of PCl.sub.3 before the polymerization reaction is quenched and when Mooney viscosity of polybutadiene has reached a prefixed value, preferably lower than, or equal to 30; the polymerization of butadiene is carried out in a solution in an aliphatic or cycloaliphatic solvent, in the presence of a catalytic system based on rare earths, preferably a neodymium-based catalytic system.

Abstract: A method is disclosed for preparing complexes of metals of the VIII Group of the Periodic Table, useful as hydrogenation catalysts. The method, as a single-step process, comprises reacting a polymeric complex containing V Group elements and VIII Group metal compounds directly with a metal atom which is directly bound to the V group element in the presence of a reducing substance. The reducing substance is selected among alkali metal and alkaline earth metal hydrides, mixed alkaline-III group element hydrides, organic metallic compounds of III Group metals, alkali metal and alkaline earth metal alkyls, Grignard compounds.