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, X2, X3 and X4, 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.