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: wherein: Mn is a manganese atom or a manganese ion in oxidation state to; 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 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 to; 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 is charged, the catalyst comprises one or more additional counterions to balance the charge of the complex.