Alkylidene complexes of ruthenium containing N-heterocyclic carbene ligands; use as highly active, selective catalysts for olefin metathesis

A complex of ruthenium of the structural formula I,

• where X1 and X2 are identical or different and are each an anionic ligand,
• R1 and R2 are identical or different and are each hydrogen or a hydrocarbon group, where the hydrocarbon groups are identical or different and are selected independently from among straight-chain, branched, cyclic or noncyclic radicals from the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having up to 50 carbon atoms, alkynyl radicals having up to 50 carbon atoms, aryl radicals having from up to 30 carbon atoms and silyl radicals, or R1 and R2 form a ring,
• where one or more of the hydrogen atoms in the hydrocarbon or silyl groups or both the hydrocarbon and silyl group can be replaced independently by identical or different alkyl, aryl, alkenyl, alkynyl, metallocenyl, halogen, nitro, nitroso, hydroxy, alkoxy, aryloxy, amino, amido, carboxyl, carbonyl, thio or sulfonyl groups, the ligand L1 is an N-heterocyclic carbene of the formula II and the ligand L2 is an amine, imine, phosphine, phosphite, stibine, arsine, carbonyl compound, carboxyl compound, nitrile, alcohol, ether, thiol or thioether
• where R1, R2, R3 and R4 in formula II are identical or different and are each hydrogen or a hydrocarbon group,
• where the hydrocarbon groups comprise identical or different, cyclic, noncyclic, straight-chain or/and branched radicals selected from the group consisting of alkyl radicals having from 1 to 50 carbon atoms, alkenyl radicals having up to 50 carbon atoms, alkynyl radicals having up to 50 carbon atoms and aryl radicals having up to 30 carbon atoms, in which at least one hydrogen may be replaced by functional groups, and where one or both of R3 and R4 may be identical or different halogen, nitro, nitroso, alkoxy, aryloxy, amido, carboxyl, carbonyl, thio or sulfonyl groups.