An oxo-nitrogenated vanadium complex having the general formula (I): in which: R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7, mutually identical or different, represent a hydrogen atom; or are selected from optionally halogenated, linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, optionally substituted cycloalkyl groups, optionally substituted aryl groups; X.sub.1 and X.sub.2, mutually identical or different, represent a halogen atom such as, for example, chlorine, bromine, iodine, preferably chlorine; or are selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, —OCOR.sub.8 groups or —OR.sub.8 groups in which R.sub.8 is selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups; Y is selected from ethers such as, for example, diethyl ether, tetrahydrofuran (THF), dimethoxyethane, preferably is tetrahydrofuran (THF); n is 0 or 1. Said oxo-nitrogenated vanadium complex having the general formula (I) may advantageously be used in a catalytic system for (co)polymerising conjugated dienes.

An oxo-nitrogenated vanadium complex having the general formula (I): in which: R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7, mutually identical or different, represent a hydrogen atom; or are selected from optionally halogenated, linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, optionally substituted cycloalkyl groups, optionally substituted aryl groups; X.sub.1 and X.sub.2, mutually identical or different, represent a halogen atom such as, for example, chlorine, bromine, iodine, preferably chlorine; or are selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, —OCOR.sub.8 groups or —OR.sub.8 groups in which R.sub.8 is selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups; Y is selected from ethers such as, for example, diethyl ether, tetrahydrofuran (THF), dimethoxyethane, preferably is tetrahydrofuran (THF); n is 0 or 1. Said oxo-nitrogenated vanadium complex having the general formula (I) may advantageously be used in a catalytic system for (co)polymerising conjugated dienes.

An oxo-nitrogenated vanadium complex having the general formula (I): in which: R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7, mutually identical or different, represent a hydrogen atom; or are selected from optionally halogenated, linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, optionally substituted cycloalkyl groups, optionally substituted aryl groups; X.sub.1 and X.sub.2, mutually identical or different, represent a halogen atom such as, for example, chlorine, bromine, iodine, preferably chlorine; or are selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, OCOR.sub.8 groups or OR.sub.8 groups in which R.sub.8 is selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups; Y is selected from ethers such as, for example, diethyl ether, tetrahydrofuran (THF), dimethoxyethane, preferably is tetrahydrofuran (THF); n is 0 or 1. Said oxo-nitrogenated vanadium complex having the general formula (I) may advantageously be used in a catalytic system for (co)polymerizing conjugated dienes.

An oxo-nitrogenated vanadium complex having the general formula (I): in which: R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7, mutually identical or different, represent a hydrogen atom; or are selected from optionally halogenated, linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, optionally substituted cycloalkyl groups, optionally substituted aryl groups; X.sub.1 and X.sub.2, mutually identical or different, represent a halogen atom such as, for example, chlorine, bromine, iodine, preferably chlorine; or are selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups, OCOR.sub.8 groups or OR.sub.8 groups in which R.sub.8 is selected from linear or branched C.sub.1-C.sub.20, preferably C.sub.1-C.sub.15, alkyl groups; Y is selected from ethers such as, for example, diethyl ether, tetrahydrofuran (THF), dimethoxyethane, preferably is tetrahydrofuran (THF); n is 0 or 1. Said oxo-nitrogenated vanadium complex having the general formula (I) may advantageously be used in a catalytic system for (co)polymerizing conjugated dienes.