Nitrogen titanium complex having general formula (I) or (II), wherein: - R1 represents a hydrogen atom; or is selected from linear or branched C1-C20 alkyl groups, preferably C1-C15, optionally halogenated, cycloalkyl groups optionally substituted, aryl groups optionally substituted; - R2, R3, R4 and R5, identical or different, represent a hydrogen atom; or are selected from linear or branched C1-C20 alkyl groups, preferably C1-C15, optionally halogenated, cycloalkyl groups optionally substituted, aryl groups optionally substituted, nitro groups, hydroxyl groups, amino groups; - Y represents a NH-R6 group wherein R6 represents a hydrogen atom, or is selected from linear or branched C1-C20 alkyl groups, preferably C1-C15, optionally halogenated, cycloalkyl groups optionally substituted, aryl groups optionally substituted; or a N-R7 group wherein R7 is selected from linear or branched C1-C20 alkyl groups, preferably C1-C15, optionally halogenated, cycloalkyl groups optionally substituted, aryl groups optionally substituted; - X1, X 2, X 3 and X 4, identical or different, represent a halogen atom, such as, for example, chlorine, bromine, iodine, preferably chlorine; or are selected from linear or branched C1 -C20 alkyl groups, preferably C1-C15, -OCOR8 or -OR8 groups wherein R8 is selected from linear or branched C1-C20 alkyl groups, preferably C1-C15; or one of X1, X2 and X3 is selected from ethers, such as,for example, diethylether, tetrahydrofuran (THF), dimethoxyethane, preferably tetrahydrofuran (THF); - n is 1 in the case wherein Y represents a NH-R6 group wherein R6 has the same meanings reported above; or is 0 in the case wherein Y represents a N-R7 group wherein R7 has the same meanings reported above, or in the case wherein one of X1, X2 and X3 is selected from ethers; - R'1, R' 2, R'3, R'4, R'5, R'6 and R'7, identical or different, represent a hydrogen atom; or are selected from linear or branched C1-C20 alkyl groups, preferably C1-C15, optionally halogenated, cycloalkyl groups optionally substituted, aryl groups optionally substituted; - X'1 and X'2, identical or different, represent a halogen atom such as, for example, chlorine, bromine, iodine, preferably chlorine; or are selected from linear or branched C1-C20 alkyl groups, preferably C1-C15, -OCOR'8 groups or -OR'8 groups wherein R' 8 is selected from linear or branched C1-C20 alkyl groups, preferably C1-C15; - Y' is selected from ethers such as, for example,diethylether, tetrahydrofuran (THF), dimethoxyethane, preferably is tetrahydrofuran (THF); or Y' represents a group having general formula (III), wherein R'1, R' 2, R'3, R'4, R'5, R'6 and R'7, have the same meanings as reported above; - m is 0 or 1. Said nitrogen titanium complex having general formula (I) or (II) can be advantageously used in a catalytic system for the (co)polymerization of conjugated dienes.