Bisimine compounds of the formula (I) where the symbols have the following meanings: A is a nonmetal selected from among N, S, O and P, R1 is a radical of the formula NR5R6, R2 is a radical of the formula NR5R6 or NR7R8, alkyl, aryl or cycloalkyl, R5 and R6 together with the N atom form a 5-, 6- or 7-membered ring in which one or more of the —CH— or —CH2— groups may be replaced by suitable heteroatom groups and which may be saturated or unsaturated and unsubstituted or substituted or be fused with further carbacyclic or heterocarbacyclic 5- or 6-membered rings which may in turn be saturated or unsaturated and substituted or unsubstituted, and R7 and R8 are, independently of one another, alkyl, aryl or cycloalkyl radicals, and R3, R4 are, independently of one another, H or alkyl, aryl or cycloalkyl radicals, and n is 1 or 2, are used to prepare bisimidinato complexes which can be used in the polymerization of unsaturated compounds.