A method comprising hydrogenating an ester in the presence of (i) a base, wherein the conjugate acid of the base has a pKa, determined in water at 25 °C, of from 6.4 to 14, (ii) hydrogen gas and (iii) a catalyst comprising a charged or neutral complex of formula (I): wherein: Mn is a manganese atom or a manganese ion in oxidation state (I) to (VII); R 1 and R 2 are each independently C 1-20 hydrocarbyl or heterocyclyl moieties, optionally substituted one or more times with a substituent selected from the group consisting of halo, aliphatic C 1-6 hydrocarbyl, trihalomethyl, aryl, heteroaryl, hydroxy, nitro, amino, alkoxy, alkylthio, carboxylate, sulfonate, phosphate, cyano, thio, formyl, ester, acyl, thioacyl, carbamido and sulfonamido; -Fc- denotes a ferrocene ( bis (η 5 -cyclopentadienyl)iron) moiety covalently bonded via adjacent carbon atoms of one of the two cyclopentadienyl moieties, and which may be optionally further substituted, in either cyclopentadienyl ring, one or more times with a substituent selected from the group consisting of halo, aliphatic C 1-6 hydrocarbyl, trihalomethyl, aryl, heteroaryl, hydroxy, nitro, amino, alkoxy, alkylthio, carboxylate, sulfonate, phosphate, cyano, thio, formyl, ester, acyl, thioacyl, carbamido and sulfonamido; -Z- is an alkylene linker of the formula -(CH 2 ) 1-6 - in which one or more of the hydrogen atoms of the alkylene may be independently substituted with an alkyl, aryl, heteroaryl, hydroxy, nitro, amino, alkoxy, alkylthio or thiol substituent; -N x is a nitrogen-containing amino, imino or heteroaryl moiety; and L 1 -L 3 constitute one, two or three ligands in which each of L 1 -L 3 independently represents a monodentate neutral or anionic ligand; or one of L 1 -L 3 represents a monodentate neutral or anionic ligand and the other two of L 1 -L 3 together represent a bidentate neutral or anionic ligand; or L 1 -L 3 together represent a tridentate neutral or anionic ligand, wherein, when the complex of formula (I) is charged, the catalyst comprises one or more additional counterions to balance the charge of the complex. Mn is a manganese atom or a manganese ion in oxidation state (I) to (VII); R 1 and R 2 are each independently C 1-20 hydrocarbyl or heterocyclyl moieties, optionally substituted one or more times with a substituent selected from the group consisting of halo, aliphatic C 1-6 hydrocarbyl, trihalomethyl, aryl, heteroaryl, hydroxy, nitro, amino, alkoxy, alkylthio, carboxylate, sulfonate, phosphate, cyano, thio, formyl, ester, acyl, thioacyl, carbamido and sulfonamido; -Fc- denotes a ferrocene ( bis (η 5 -cyclopentadienyl)iron) moiety covalently bonded via adjacent carbon atoms of one of the two cyclopentadienyl moieties, and which may be optionally further substituted, in either cyclopentadienyl ring, one or more times with a substituent selected from the group consisting of halo, aliphatic C 1-6 hydrocarbyl, trihalomethyl, aryl, heteroaryl, hydroxy, nitro, amino, alkoxy, alkylthio, carboxylate, sulfonate, phosphate, cyano, thio, formyl, ester, acyl, thioacyl, carbamido and sulfonamido; -Z- is an alkylene linker of the formula -(CH 2 ) 1-6 - in which one or more of the hydrogen atoms of the alkylene may be independently substituted with an alkyl, aryl, heteroaryl, hydroxy, nitro, amino, alkoxy, alkylthio or thiol substituent; -N x is a nitrogen-containing amino, imino or heteroaryl moiety; and L 1 -L 3 constitute one, two or three ligands in which each of L 1 -L 3 independently represents a monodentate neutral or anionic ligand; or one of L 1 -L 3 represents a monodentate neutral or anionic ligand and the other two of L 1 -L 3 together represent a bidentate neutral or anionic ligand; or L 1 -L 3 together represent a tridentate neutral or anionic ligand, wherein, when the complex of formula (I) is charged, the catalyst comprises one or more additional counterions to balance the charge of the complex. <EOS>