An uncharged transition metal complex of formula wherein the symbols have the following meanings: M1 is Ru, Rh, Ir, Pt in any oxidation state possible for the respective metal atom; L is a monoanionic or dianionic ligand, which may be monodentate or bidentate; K is an uncharged monodentate or bidentate ligand; n is the number of carbene ligands, wherein n is at least 2 and the carbene ligands in the complex of the formula I can be identical or different; m is the number of ligands L, wherein m can be 0 or ≥1 and when m>1, the ligands L can be identical or different; o is the number of ligands K, wherein o can be 0 or ≥1 and when o>1 the ligands K can be identical or different; wherein the sum n+m+o is dependent on the oxidation state and coordination number of the metal atom and on the denticity of the ligands and also on the charge of the ligands, with the proviso that n is at least 2; Do 2 is a donor atom selected from the group consisting of C, N, P, O and S; s is 2 when Do 2 is C, is 1 when Do2 is N or P and is 0 when Do 2 is O or S; X is a spacer selected from the group consisting of silylene, alkylene, arylene, heteroarylene and alkenylene; p is 0 or 1; q is 0 or 1; Y 3 is hydrogen or an alkyl, aryl, heteroaryl or alkenyl radical; or wherein Do 2', q', s', R 3', R 1', R 2', X' and p' are each, independently of one another, as defined for Do 2, q, s, R 3, R 1, R 2, X and p; R 1, R 2 are each, independently of one another, hydrogen or alkyl, aryl, heteroaryl or alkenyl radicals, or R 1 and R 2 together form a bridge having a total of from three to five atoms of which one or two atoms may be heteroatoms and the remaining atoms are carbon atoms, so that the group forms a five- to seven-membered ring which may contain, in addition to the existing double bond, one further double bond or in the case of a six- or seven-membered ring two further double bonds and may be substituted by alkyl or aryl groups, or the ring is fused-on to further rings, which may contain at least one heteroatom; R 3 is hydrogen or an alkyl, aryl, heteroaryl or alkenyl radical; Y 1, Y 2 together form a bridge between the nitrogen atoms N which has at least two atoms of which at least one is a carbon atom, wherein the bridge may be saturated or unsaturated and the two atoms may be substituted or unsubstituted, wherein in case the bridge has two carbon atoms and is satutared at least one of the two carbon atoms is substituted, characterized in that the group in at least one of the at least 2 carben ligands has the formula c wherein the symbols have the following meanings: R 10 is alkyl, aryl, heteroaryl or alkenyl or 2 radicals R 10 together form a fused-on ring, which may contain at least one heteroatom, or R10 is a radical which acts as a donor or acceptor; v is 0 to 4, and when v is 0 the four carbon atoms of the aryl radical in the formula c which may be substituted by R 10 bear hydrogen atoms; Y 3 is a hydrogen atom or an alkyl, aryl, heteroaryl or alkenyl radical; or wherein Do 2', q', s', R 3', R 1', R 2', X' and p' are each, independently of one another, as defined for Do 2, q, s, R 3, R 1, R 2, X and p. M1 is Ru, Rh, Ir, Pt in any oxidation state possible for the respective metal atom; L is a monoanionic or dianionic ligand, which may be monodentate or bidentate; K is an uncharged monodentate or bidentate ligand; n is the number of carbene ligands, wherein n is at least 2 and the carbene ligands in the complex of the formula I can be identical or different; m is the number of ligands L, wherein m can be 0 or ≥1 and when m>1, the ligands L can be identical or different; o is the number of ligands K, wherein o can be 0 or ≥1 and when o>1 the ligands K can be identical or different; Do 2 is a donor atom selected from the group consisting of C, N, P, O and S; s is 2 when Do 2 is C, is 1 when Do2 is N or P and is 0 when Do 2 is O or S; X is a spacer selected from the group consisting of silylene, alkylene, arylene, heteroarylene and alkenylene; p is 0 or 1; q is 0 or 1; Y 3 is hydrogen or an alkyl, aryl, heteroaryl or alkenyl radical; or wherein Do 2', q', s', R 3', R 1', R 2', X' and p' are each, independently of one another, as defined for Do 2, q, s, R 3, R 1, R 2, X and p; R 1, R 2 are each, independently of one another, hydrogen or alkyl, aryl, heteroaryl or alkenyl radicals, or R 1 and R 2 together form a bridge having a total of from three to five atoms of which one or two atoms may be heteroatoms and the remaining atoms are carbon atoms, so that the group forms a five- to seven-membered ring which may contain, in addition to the existing double bond, one further double bond or in the case of a six- or seven-membered ring two further double bonds and may be substituted by alkyl or aryl groups, or the ring is fused-on to further rings, which may contain at least one heteroatom; R 3 is hydrogen or an alkyl, aryl, heteroaryl or alkenyl radical; Y 1, Y 2 together form a bridge between the nitrogen atoms N which has at least two atoms of which at least one is a carbon atom, wherein the bridge may be saturated or unsaturated and the two atoms may be substituted or unsubstituted, wherein in case the bridge has two carbon atoms and is satutared at least one of the two carbon atoms is substituted, R 10 is alkyl, aryl, heteroaryl or alkenyl or 2 radicals R 10 together form a fused-on ring, which may contain at least one heteroatom, or R10 is a radical which acts as a donor or acceptor; v is 0 to 4, and when v is 0 the four carbon atoms of the aryl radical in the formula c which may be substituted by R 10 bear hydrogen atoms; Y 3 is a hydrogen atom or an alkyl, aryl, heteroaryl or alkenyl radical; or