Compound of formula: in which: X, X' are chlorine; R 1 and R 2 are independently a hydrogen, a C 1 to C 6 alkyl, a C 1 to C 6 perhaloalkyl, an aldehyde, a nitrile, a cyclohexyl, a C n H 2n Y or C n F 2n Y radical with n between 1 and 6 and Y an ionic marker, or a radical of formula: it being possible for R 1 to be chosen in addition from the group consisting of C 6 F 5, pNO 2 C 6 H 4 and a radical of formula (Ia): R 3 is a C 1 to C 6 alkyl or a C 5 or C 6 cycloalkyl or a C 5 or C 6 aryl; R 4, R 5, R 6, R 7, R 8, R 9, R 10 and R 11 are independently a hydrogen, a C 1 to C 6 alkyl, a C 1 to C 6 perhaloalkyl or a C 5 or C 6 aryl, it being possible for R 9, R 10 and R 11 to form a heterocycle; X 1 is an anion: halogen, tetrafluoroborate ([BF 4] -), [tetrakis(3,5-bis(trifluoromethyl)phenyl)borate] ([BARF] -), hexafluorophosphate ([PF 6] -), hexafluoroantimonate ([SbF 6] -), hexafluoroarsenate ([AsF 6] -) or trifluoromethylsulphonate ([(CF 3) 2 N] -); it being possible for R 1 and R 2 to form, with the N and the C to which they are attached, a heterocycle of formula: hal being a halogen and R 12 being a hydrogen, a C 1 to C 6 alkyl, a C 5 or C 6 cycloalkyl or a C 5 or C 6 aryl; L is a ligand of formula 7a or 7b: in which: n 1 = 0, 1, 2 or 3; R 14, R 15, R 16, R 17, R 18 and R 19 are independently a C 1 to C 6 alkyl, a C 3 to C 20 cycloalkyl, a C 2 to C 20 alkenyl, a naphthyl, an anthracene or a phenyl, it being possible for the said phenyl to be substituted by up to 5 groups chosen from C 1 to C 6 alkyls, C 1 to C 6 alkoxyls and halogens and it being possible for R 16 and R 17 to form a 3-, 4-, 5-, 6- or 7-membered ring; or L is PCy 3, Cy being cyclohexyl. X, X' are chlorine; R 1 and R 2 are independently a hydrogen, a C 1 to C 6 alkyl, a C 1 to C 6 perhaloalkyl, an aldehyde, a nitrile, a cyclohexyl, a C n H 2n Y or C n F 2n Y radical with n between 1 and 6 and Y an ionic marker, or a radical of formula: it being possible for R 1 to be chosen in addition from the group consisting of C 6 F 5, pNO 2 C 6 H 4 and a radical of formula (Ia): R 3 is a C 1 to C 6 alkyl or a C 5 or C 6 cycloalkyl or a C 5 or C 6 aryl; R 4, R 5, R 6, R 7, R 8, R 9, R 10 and R 11 are independently a hydrogen, a C 1 to C 6 alkyl, a C 1 to C 6 perhaloalkyl or a C 5 or C 6 aryl, it being possible for R 9, R 10 and R 11 to form a heterocycle; X 1 is an anion: halogen, tetrafluoroborate ([BF 4] -), [tetrakis(3,5-bis(trifluoromethyl)phenyl)borate] ([BARF] -), hexafluorophosphate ([PF 6] -), hexafluoroantimonate ([SbF 6] -), hexafluoroarsenate ([AsF 6] -) or trifluoromethylsulphonate ([(CF 3) 2 N] -); it being possible for R 1 and R 2 to form, with the N and the C to which they are attached, a heterocycle of formula: hal being a halogen and R 12 being a hydrogen, a C 1 to C 6 alkyl, a C 5 or C 6 cycloalkyl or a C 5 or C 6 aryl; L is a ligand of formula 7a or 7b: in which: n 1 = 0, 1, 2 or 3; R 14, R 15, R 16, R 17, R 18 and R 19 are independently a C 1 to C 6 alkyl, a C 3 to C 20 cycloalkyl, a C 2 to C 20 alkenyl, a naphthyl, an anthracene or a phenyl, it being possible for the said phenyl to be substituted by up to 5 groups chosen from C 1 to C 6 alkyls, C 1 to C 6 alkoxyls and halogens and it being possible for R 16 and R 17 to form a 3-, 4-, 5-, 6- or 7-membered ring; or L is PCy 3, Cy being cyclohexyl. n 1 = 0, 1, 2 or 3; R 14, R 15, R 16, R 17, R 18 and R 19 are independently a C 1 to C 6 alkyl, a C 3 to C 20 cycloalkyl, a C 2 to C 20 alkenyl, a naphthyl, an anthracene or a phenyl, it being possible for the said phenyl to be substituted by up to 5 groups chosen from C 1 to C 6 alkyls, C 1 to C 6 alkoxyls and halogens and it being possible for R 16 and R 17 to form a 3-, 4-, 5-, 6- or 7-membered ring; or L is PCy 3, Cy being cyclohexyl.