Process for the preparation of (co) polymers of conjugated dienes which comprises polymerizing at least one conjugated diene in the presence of a catalytic system comprising at least one oxo-nitrogenated complex of cobalt having general formula (I), wherein: R.sub.1 and R.sub.2, equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, optionally halogenated; cycloalkyl groups optionally substituted; aryl groups optionally substituted; Y represents an oxygen atom; or a group NR.sub.3 wherein R.sub.3 represents a hydrogen atom, or it is selected from linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups, optionally halogenated, cycloalkyl groups optionally substituted-; aryl groups optionally substituted; or, when Y represents a group NR.sub.3, R.sub.2 and R.sub.3 can be optionally bound to each other to form, together with the other atoms to which they are bound, a cycle containing from 3 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally substituted with linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups, said cycle optionally containing heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; X.sub.1 and X.sub.2, equal to or different from each other, represent a halogen atom such as, for example, chlorine, bromine, iodine; or they are selected from linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups, OCOR.sub.4 groups or OR.sub.4 groups wherein R.sub.4 is selected from linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups. ##STR00001##

Process for the preparation of (co) polymers of conjugated dienes which comprises polymerizing at least one conjugated diene in the presence of a catalytic system comprising at least one oxo-nitrogenated complex of cobalt having general formula (I), wherein: R.sub.1 and R.sub.2, equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, optionally halogenated; cycloalkyl groups optionally substituted; aryl groups optionally substituted; Y represents an oxygen atom; or a group NR.sub.3 wherein R.sub.3 represents a hydrogen atom, or it is selected from linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups, optionally halogenated, cycloalkyl groups optionally substituted-; aryl groups optionally substituted; or, when Y represents a group NR.sub.3, R.sub.2 and R.sub.3 can be optionally bound to each other to form, together with the other atoms to which they are bound, a cycle containing from 3 to 6 carbon atoms, saturated, unsaturated, or aromatic, optionally substituted with linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups, said cycle optionally containing heteroatoms such as, for example, oxygen, sulfur, nitrogen, silicon, phosphorous, selenium; X.sub.1 and X.sub.2, equal to or different from each other, represent a halogen atom such as, for example, chlorine, bromine, iodine; or they are selected from linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups, OCOR.sub.4 groups or OR.sub.4 groups wherein R.sub.4 is selected from linear or branched C.sub.1-C.sub.20 preferably C.sub.1-C.sub.15, alkyl groups. ##STR00001##