A ruthenium complex of the formula 1: wherein: L is a neutral ligand; X 1 and X 2 independently represent an anionic ligand; R 1, R 2, R a, R b, R c, R d independently represent a hydrogen atom, a halogen atom, C 1 -C 25 alkyl, C 1 -C 25 perfluoroalkyl, C 3 -C 7 cycloalkyl, C 2 -C 25 alkenyl, C 3 -C 25 cycloalkenyl, C 2 -C 25 alkynyl, C 3 -C 25 cycloalkynyl, C 1 -C 25 alkoxy, C 5 -C 24 aryl, C 5 -C 20 heteroaryl, 3-12-membered heterocyclyl, ether (-OR'), thioether (-SR'), nitro (-NO 2), cyano (-CN), carboxy and ester (-COOR'), amido (-CONR'R"), sulphono (-SO 2 R'), sulphonamido (-SO 2 NR'R"), formyl and keto (-COR'), wherein R' and R" independently represent a hydrogen atom, C 1 -C 5 alkyl, C 1 -C 5 perfluoroalkyl, C 5 -C 24 aryl, C 5 -C 24 heteroaryl, C 5 -C 24 perfluoroaryl; Z independently represents a formyl and keto (-COR Z '), carboxy and ester (-COOR Z '), thioester (-CSOR Z '), nitro (-NO 2), amido (-CONR Z 'R Z "), sulphono (-SO 2 R Z '), sulphonamido (-SO 2 NR Z 'R Z "), -CR Z 'R Z "COR Z ', -CR Z 'R Z "COOR Z ', - CR Z 'R Z "CONR Z 'R Z ", -CR Z 'R Z "SO 2 R Z ', -CR Z 'R Z "SO 2 NR Z 'R Z "; wherein R Z ' and R Z " independently represent a hydrogen atom, C 1 -C 5 alkyl, C 1 -C 5 perfluoroalkyl, C 5 -C 24 aryl, C 5 -C 24 heteroaryl, C 5 -C 24 perfluoroaryl; the anionic ligands X 1, X 2 independently represent a halogen atom, -CN, -SCN, -OR 4, -SR 4, -O(C=O)R 4, -O(SO 2)R 4, -OP R 2 4, -OSiR 3 4, where R 4 is C 1 -C 12 alkyl, C 3 -C 12 cycloalkyl, C 2 -C 12 alkenyl, or C 5 -C 20 aryl, being optionally substituted with at least one C 1 -C 12 alkyl, C 1 -C 12 perhaloalkyl, C 1 -C 12 alkoxy or a halogen atom; and also the neutral ligand L is selected independently from the group comprising so called N-heterocyclic carbene ligands represented by the formula 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j, 2k, 2l, 2m, 2n, 2o or 2p: wherein: each R 50, R 60, R 70 and R 80 independently represents C 1 -C 12 alkyl, C 3 -C 12 cycloalkyl, C 2 -C 12 alkenyl, C 5 -C 20 aryl, or C 5 -C 20 heteroaryl, being optionally substituted with at least one C 1 -C 12 alkyl, C 1 -C 12 perhaloalkyl, C 1 -C 12 alkoxy or a halogen atom; each R 5, R 6, R 7, R 8, R 9 and R 10 independently represents a hydrogen atom, C 1 -C 12 alkyl, C 3 -C 12 cycloalkyl, C 2 -C 12 alkenyl, C 5 -C 20 aryl, or C 5 -C 20 heteroaryl, being optionally substituted with at least one C 1 -C 12 alkyl, C 1 -C 12 perhaloalkyl, C 1 -C 12 alkoxy or a halogen atom; and any substituents selected from the group comprising R 5, R 6, R 7, R 8, R 9 and R 10 as well as R 50, R 60, R 70 and R 80 may optionally bind each other to form a cyclic or macrocyclic system. L is a neutral ligand; X 1 and X 2 independently represent an anionic ligand; R 1, R 2, R a, R b, R c, R d independently represent a hydrogen atom, a halogen atom, C 1 -C 25 alkyl, C 1 -C 25 perfluoroalkyl, C 3 -C 7 cycloalkyl, C 2 -C 25 alkenyl, C 3 -C 25 cycloalkenyl, C 2 -C 25 alkynyl, C 3 -C 25 cycloalkynyl, C 1 -C 25 alkoxy, C 5 -C 24 aryl, C 5 -C 20 heteroaryl, 3-12-membered heterocyclyl, ether (-OR'), thioether (-SR'), nitro (-NO 2), cyano (-CN), carboxy and ester (-COOR'), amido (-CONR'R"), sulphono (-SO 2 R'), sulphonamido (-SO 2 NR'R"), formyl and keto (-COR'), wherein R' and R" independently represent a hydrogen atom, C 1 -C 5 alkyl, C 1 -C 5 perfluoroalkyl, C 5 -C 24 aryl, C 5 -C 24 heteroaryl, C 5 -C 24 perfluoroaryl; Z independently represents a formyl and keto (-COR Z '), carboxy and ester (-COOR Z '), thioester (-CSOR Z '), nitro (-NO 2), amido (-CONR Z 'R Z "), sulphono (-SO 2 R Z '), sulphonamido (-SO 2 NR Z 'R Z "), -CR Z 'R Z "COR Z ', -CR Z 'R Z "COOR Z ', - CR Z 'R Z "CONR Z 'R Z ", -CR Z 'R Z "SO 2 R Z ', -CR Z 'R Z "SO 2 NR Z 'R Z "; wherein R Z ' and R Z " independently represent a hydrogen atom, C 1 -C 5 alkyl, C 1 -C 5 perfluoroalkyl, C 5 -C 24 aryl, C 5 -C 24 heteroaryl, C 5 -C 24 perfluoroaryl; the anionic ligands X 1, X 2 independently represent a halogen atom, -CN, -SCN, -OR 4, -SR 4, -O(C=O)R 4, -O(SO 2)R 4, -OP R 2 4, -OSiR 3 4, where R 4 is C 1 -C 12 alkyl, C 3 -C 12 cycloalkyl, C 2 -C 12 alkenyl, or C 5 -C 20 aryl, being optionally substituted with at least one C 1 -C 12 alkyl, C 1 -C 12 perhaloalkyl, C 1 -C 12 alkoxy or a halogen atom; and also the neutral ligand L is selected independently from the group comprising so called N-heterocyclic carbene ligands represented by the formula 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j, 2k, 2l, 2m, 2n, 2o or 2p: each R 50, R 60, R 70 and R 80 independently represents C 1 -C 12 alkyl, C 3 -C 12 cycloalkyl, C 2 -C 12 alkenyl, C 5 -C 20 aryl, or C 5 -C 20 heteroaryl, being optionally substituted with at least one C 1 -C 12 alkyl, C 1 -C 12 perhaloalkyl, C 1 -C 12 alkoxy or a halogen atom; each R 5, R 6, R 7, R 8, R 9 and R 10 independently represents a hydrogen atom, C 1 -C 12 alkyl, C 3 -C 12 cycloalkyl, C 2 -C 12 alkenyl, C 5 -C 20 aryl, or C 5 -C 20 heteroaryl, being optionally substituted with at least one C 1 -C 12 alkyl, C 1 -C 12 perhaloalkyl, C 1 -C 12 alkoxy or a halogen atom; and any substituents selected from the group comprising R 5, R 6, R 7, R 8, R 9 and R 10 as well as R 50, R 60, R 70 and R 80 may optionally bind each other to form a cyclic or macrocyclic system.