A process for the preparation of a catalyst having the following formula: wherein X 1 denotes an anionic ligand; L 1 is a neutral electron donor ligand; R' and R" together form a benzylidene moiety; S 1 to S 4 may be the same or different and are defined as for the compound of formula shown below; A is heteroaryl, substituted or unsubstituted alkyl, heteroalkyl or cycloalkyl. B is hydrogen, C 1 -C 20 alkyl, C 1 -C 20 heteroalkyl aryl or heteroaryl, wherein each non-hydrogen group may be optionally substituted with one or more moieties selected from the group consisting of C 1 -C 10 alkyl and aryl; R o1, R o2, R m1, R m2 and R p are each selected from the group consisting of hydrogen, C 1 -C 20 alkyl, C 1 -C 20 heteroalkyl C 1 -C 20 alkoxy, aryl, aryloxy, heteroaryl, heterocyclolalkyl, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate and halogen, thioether, ketone, aldehyde, ester, ether, amine, amide, nitro, carboxylic acid, the non-hydrogen groups optionally substituted with one or more moieties selected from the group consisting of C 1 -C 20 alkyl, C 1 -C 20 alkoxy and aryl, wherein R o1, R o2, R m1, R m2 and R p can be joined to form a fused cyclic aliphatic or aromatic ring optionally substituted with one or more moieties selected from the group consisting of C 1 -C 20 alkyl, C 1 -C 20 heteroalkyl, C 1 -C 20 alkoxy, aryl, aryloxy, heteroaryl, heterocycloalkyl, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate and halogen, thioether, ketone, aldehyde, ester, ether, amine, amide, nitro, carboxylic acid, the non-hydrogen groups optionally substituted with one or more moieties selected from the group consisting of C 1 -C 20 alkyl, C 1 -C 20 alkoxy and aryl, comprising the following. steps: (i) reacting a compound of the formula wherein PL 1 and PL 2 denote a phosphine ligand, X 1 and X 2 denote an anionic ligand and R' and R" are as defined above, with a precursor of a non-phosphine ligand L 1 as defined above to obtain a compound of the formula wherein L 1, PL 2, X 1,X 2, R' and R" are as defined above, and (ii) reacting the compound of formula with a compound of the formula wherein A and B are as defined above and wherein S 1 to S 4 are substituents which are selected such that the compound of the formula has a pK a ≥ 6.2, in the presence of a weak base having a pK b in the range of 3.5 - 7.0. X 1 denotes an anionic ligand; L 1 is a neutral electron donor ligand; R' and R" together form a benzylidene moiety; S 1 to S 4 may be the same or different and are defined as for the compound of formula shown below; A is heteroaryl, substituted or unsubstituted alkyl, heteroalkyl or cycloalkyl. B is hydrogen, C 1 -C 20 alkyl, C 1 -C 20 heteroalkyl aryl or heteroaryl, wherein each non-hydrogen group may be optionally substituted with one or more moieties selected from the group consisting of C 1 -C 10 alkyl and aryl; R o1, R o2, R m1, R m2 and R p are each selected from the group consisting of hydrogen, C 1 -C 20 alkyl, C 1 -C 20 heteroalkyl C 1 -C 20 alkoxy, aryl, aryloxy, heteroaryl, heterocyclolalkyl, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate and halogen, thioether, ketone, aldehyde, ester, ether, amine, amide, nitro, carboxylic acid, the non-hydrogen groups optionally substituted with one or more moieties selected from the group consisting of C 1 -C 20 alkyl, C 1 -C 20 alkoxy and aryl, wherein R o1, R o2, R m1, R m2 and R p can be joined to form a fused cyclic aliphatic or aromatic ring optionally substituted with one or more moieties selected from the group consisting of C 1 -C 20 alkyl, C 1 -C 20 heteroalkyl, C 1 -C 20 alkoxy, aryl, aryloxy, heteroaryl, heterocycloalkyl, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate and halogen, thioether, ketone, aldehyde, ester, ether, amine, amide, nitro, carboxylic acid, the non-hydrogen groups optionally substituted with one or more moieties selected from the group consisting of C 1 -C 20 alkyl, C 1 -C 20 alkoxy and aryl, comprising the following. steps: (i) reacting a compound of the formula wherein PL 1 and PL 2 denote a phosphine ligand, X 1 and X 2 denote an anionic ligand and R' and R" are as defined above, with a precursor of a non-phosphine ligand L 1 as defined above to obtain a compound of the formula wherein L 1, PL 2, X 1,X 2, R' and R" are as defined above, and (ii) reacting the compound of formula with a compound of the formula wherein A and B are as defined above and wherein S 1 to S 4 are substituents which are selected such that the compound of the formula has a pK a ≥ 6.2, in the presence of a weak base having a pK b in the range of 3.5 - 7.0. (i) reacting a compound of the formula wherein PL 1 and PL 2 denote a phosphine ligand, X 1 and X 2 denote an anionic ligand and R' and R" are as defined above, with a precursor of a non-phosphine ligand L 1 as defined above to obtain a compound of the formula wherein L 1, PL 2, X 1,X 2, R' and R" are as defined above, and (ii) reacting the compound of formula with a compound of the formula wherein A and B are as defined above and wherein S 1 to S 4 are substituents which are selected such that the compound of the formula has a pK a ≥ 6.2, in the presence of a weak base having a pK b in the range of 3.5 - 7.0.