Manganese-catalysed hydrogenation of esters

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);
• R1 and R2 are independently selected from C1-6alkyl, C3-6cycloalkyl, phenyl, naphthyl, and furanyl, wherein the phenyl, naphthyl, and furanyl are each optionally substituted one or more times with a substituent selected from the group consisting of fluoro, chloro, C1-6 alkyl, trifluoromethyl, and C1-6 alkoxy;
• -Fc- denotes a ferrocene (bis(η5-cyclopentadienyl) iron) moiety covalently bonded via adjacent carbon atoms of one of the two cyclopentadienyl moieties;
• —Z— is —(CH2)—, —(CHR3)— or —(CH2)2—, wherein R3 is an C1-6alkyl substituent or phenyl optionally substituted one or more times with C1-6alkyl and/or halo;
• —Nx is selected from the group consisting of pyridyl, quinolinyl, isoquinolinyl, pyrimidinyl, oxazolyl, isooxazolyl, imidazolyl, pyrazolyl, quinoxalinyl, pyridazinyl, triazolyl, triazinyl, imidazolidinyl and oxadiazolyl, each of which is optionally substituted one or more times with one or more substituents independently selected from the group consisting of C1-6alkyloxy, amino, halo, C1-6alkyl, and aryl;
• and
• L3 is selected from the group consisting of carbon monoxide, nitrogen monoxide, amines, ethers, thioethers, sulfoxides, nitriles, isocyanides, phosphorus-containing ligands based on either phosphorus (III) or phosphorus (V), water, halides, alkoxides, anions of carboxylic, sulfonic and phosphoric acids, amido ligands, thiolates, phosphides, cyanide, thiocyanate, isothiocyanate, and enolate ions,
• L1 and L2 are each a carbon monoxide 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.