Complexes of N-heterocyclic carbenes and the use thereof

N-Heterocyclic carbenes of the general formula (I)

• 7
• in which
• Z is a 1,2-ethanediyl or a 1,2-ethylenediyl radical and
• R1 and R2 are each, independently of one another, radicals of the general formula (II)
• CR5R6R7 (II)
• in which
• a) CR5R6R7 as a whole is a substituted or unsubstituted carbocyclic or heterocyclic radical or a substituted or unsubstituted carbopolycyclic or heteropolycyclic radical, or
• b) the radicals R5, R6 and R7 are each hydrogen or an organic radical,
• with the proviso both for a) and for b) that, of the three atoms of R5, R6 and R7 which are bonded to the carbon atom C, either
• all three are, in each case independently of one another, secondary, tertiary or quaternary carbon atoms, or
• two are, in each case independently of one another, secondary, tertiary or quaternary carbon atoms and, in the case where both of these two atoms are secondary, at least one thereof is bonded to a total of at least two tertiary or quaternary carbon atoms, and
• R3 and R4 are each independently hydrogen, C6-C12-aryl, C6-C12-arylalkyl or C1-C8-alkyl.

Salts of the general formula (X)

• 8
• in which
• Z is a 1,2 ethanediyl or a 1,2-ethenediyl radical and
• R1 and R2 are each, independently of one another, radicals of the general formula (II)
• CR5R6R7 (II)
• in which
• a) CR5R6R7 as a whole is a substituted or unsubstituted carbocyclic or heterocyclic radical or a substituted or unsubstituted carbopolycyclic or heteropolycyclic radical, or
• b) the radicals R5, R6 and R7 are each hydrogen or an organic radical,
• with the proviso both for a) and for b) that, of the three atoms of R5, R6 and R7 which are bonded to the carbon atom C, either
• all three are, in each case independently of one another, secondary, tertiary or quaternary carbon atoms, or
• two are, in each case independently of one another, secondary, tertiary or quaternary carbon atoms and, in the case where both of these two atoms are secondary, at least one thereof is bonded to a total of at least two tertiary or quaternary carbon atoms, and
• R3 and R4 are each independently hydrogen, C6-C12-aryl, C6-C12-arylalkyl or C1-C8-alkyl and
• An is the anion of an acid.

Nickel, palladium and platinum complexes which comprise as ligands at least one N-heterocyclic carbene of the general formula (I)

• 9
• in which
• Z is a 1,2-ethanediyl or a 1,2-ethylenediyl radical and
• R1 and R2 are each, independently of one another, radicals of the general formula (II)
• CR5R6R7 (II
• in which
• a) CR5R6R7 as a whole is a substituted or unsubstituted carbocyclic or heterocyclic radical or a substituted or unsubstituted carbopolycyclic or heteropolycyclic radical, or
• b) the radicals R5, R6 and R7 are each hydrogen or an organic radical,
• with the proviso both for a) and for b) that, of the three atoms of R5, R6 and R7 which are bonded to the carbon atom C, either
• all three are, in each case independently of one another, secondary, tertiary or quaternary carbon atoms, or
• two are, in each case independently of one another, secondary, tertiary or quaternary carbon atoms and, in the case where both of these two atoms are secondary, at least one thereof is bonded to a total of at least two tertiary or quaternary carbon atoms, and
• R3 and R4 are each independently hydrogen, C6-C12-aryl, C6-C12-arylalkyl or C1-C8-alkyl.

Process for preparing complexes of the general formula (VIII)

• [Pd(L)2] (VIII)
• in which the two ligands L are each, independently of one another, N-heterocyclic carbenes, characterized in that
• palladium complexes of the general formula (IX)
• [Pd(P)2] (IX)
• in which P is a monodentate phosphane ligand are reacted with an N-heterocyclic carbene in the presence of solvent.