Vanadium phosphinic complex having general formula (I) or (II): V(X)M3P̂WFys-nMO V(X)3[(R3)2P(R4)P(R3)2] (ID wherein: X represents an anion selected from halogens such as, for example, chlorine, bromine, iodine, preferably chlorine; or is selected from the following groups: thiocyanate, isocyanate, sulfate, acid sulfate, phosphate, acid phosphate, carboxylate, dicarboxylate; Ri, identical or different among them, represent a hydrogen atom, or an allyl group (CH2=CH—CH2-); or are selected from alkyl groups CrC2o, preferably CrĈ, linear or branched, optionally halogenated, optionally substituted cycloalkyl groups; —n is an integer ranging from 0 to 3; R2, identical or different among them, are selected from optionally substituted aryl groups; R3, identical or different among them, represent a hydrogen atom, or an allyl group (CH2=CH—CH2-); or are selected from alkyl groups C1-C2o, preferably CrĈ, linear or branched, optionally halogenated, optionally substituted cycloalkyl groups, optionally substituted aryl groups; R4 represents a group —NR5 wherein R5 represents a hydrogen atom, or is selected from C1-C20 alkyl groups, preferably CrC15, linear or branched; or R4 represents an alkylene group —(CH2) p- wherein p represents an integer ranging from 1 to 5; provided that in the general formula (I), in case n is equal to 1 and Ri is methyl, R2 is different from phenyl. Said phosphinic vanadium complex having general formula (I) or (II) can be advantageously used in a catalytic system for the (co)polymerization of conjugated dienes.