Method for the isomerisation of transition metal complexes containing cyclometallated, carbene ligands

A process for converting a compound C1 of the formula I in a mer isomer form

• into an isomeric compound C2 of the formula I in a fac isomer form, where the variables have the following meanings:
• n is 2 or 3;
• M is Pd or Pt, in each case in the formal oxidation state +II, when n is 2;
• and is Ru, Os, Co, Rh or Ir, in each case in the formal oxidation state +III, when n is 3;
• Do is a donor atom selected from the group consisting of N and P;
• r is 1 when Do is N or P;
• Y1, Y2 are each, independently of one another, hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, alkyloxy, aryloxy, alkylthio, arylthio, alkylcarbonyl, arylcarbonyl, carboxyl, alkyloxycarbonyl, aryloxycarbonyl, hydroxysulfonyl, alkyloxysulfonyl, aryloxysulfonyl, halogen, CN, CHO, NO2 or NO,
• or
• Y1 and Y2 together with the carbon atoms to which they are bound form a six-membered aromatic ring which may comprise one or two nitrogen atoms and may optionally be fused with a further, optionally fused and optionally heteroatom-comprising ring;
• Y3 is alkyl, alkenyl, alkynyl, aryl or heteroaryl;
• A is a bridge having three or four atoms of which one or two atoms may be heteroatoms and the remaining atoms are carbon atoms, so that the group
• forms a five- or six-membered heteroaromatic ring or benzene ring which may optionally be substituted by substituents selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, heteroaryl, alkyloxy, aryloxy, alkylthio, arylthio, alkylcarbonyl, arylcarbonyl, carboxyl, alkyloxycarbonyl, aryloxycarbonyl, hydroxysulfonyl, alkyloxysulfonyl, aryloxysulfonyl, halogen, CN, CHO, NO2 and NO and may optionally be fused with a further, optionally heteroatom-comprising ring which may likewise be fused and substituted by substituents selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, heteroaryl, alkyloxy, aryloxy, alkylthio, arylthio, alkylcarbonyl, arylcarbonyl, carboxyl, alkyloxycarbonyl, aryloxycarbonyl, hydroxysulfonyl, alkyloxysulfonyl, aryloxysulfonyl, halogen, CN, CHO, NO2 and NO;
• which comprises allowing a Brönsted acid or a mixture of Brönsted acids to act on C1 in the presence of a solvent or solvent mixture at a temperature of from 0° C. to the boiling point of the solvent or the solvent mixture, with the proviso that
• a) the formation of C2 from C1 occurs under the conditions of the process and
• b) when both C1 and C2 are present as a mixture prior to the Brönsted acid acting on C1, the respective isomer ratios of C′ and C2 are different before and after the Brönsted acid acts on C1.