Franco Piacenti

Homogeneous catalytic hydrogenation of free carboxylic acids in the presence of cluster ruthenium carbonyl hydrides

Abstract Saturated monocarboxylic acids up to C 6 , several bicarboxylic acids and some of the corresponding anhydrides are hydrogenated in the homogeneous phase with H 4 Ru 4 (CO) 8 (PBu 3 ) 4 as catalyst to give the corresponding alcohols (present among the reaction products as esters) or lactones at 100–200°C under a pressure of 100–200 atm of hydrogen. Anhydrides react at temperatures lower than those needed for acids. Esters are not reduced. Only δ-valerolactone is hydrogenated to 1,5-pentanediol. Ruthenium carbonyl carboxylates have been recovered at the end of the reaction and appear to be catalytically active intermediates.

Phosphine-substituted ruthenium carbonyl carboxylates

Abstract The behaviour of the [Ru2(CO)4(CH3COO)2]n/tributylphosphine/acetic acid system has been investigated as a function of reaction conditions and molar ratios of reactants. Tricyclohexylphosphine and triethylphosphite were also used as ligands and investigation was extended to the related oxalic, malonic, succinic, glutaric and adipic acid derivatives. These derivatives were isolated and characterized in view of their possible role as catalysts in the homogeneous hydrogenation of carboxylic acids in the presence of phosphine- or phosphite-substituted ruthenium carbonyl derivatives.

Structure and catalytic activity of phosphine-substituted ruthenium carbonyl carboxylates

Abstract The structures of the [{Ru(CO) 2 (μ-OOCCH 3 )L} 2 ] with L = P n Bu 3 , P t Bu 3 or P i Pr 3 have been determined and their catalytic activity tested in the hydrogenation of internal and terminal olefins, of the carbonyl double bond and of both free and esterified carboxylic groups. There is a correlation between the PRuRuP torsion angle and the catalytic activity of the complex.

Homogeneous catalytic hydrogenation dicarboxylic acid esters. II

Abstract Hydrogenation of dimethyl oxalate in the presence of Ru(CO)2(CH3CO-O)2(PBu3)2 gives methyl glycolate and subsequently ethylene glycol. The formation of the glycol is favoured by hydroxylated solvents.

Homogeneous catalytic hydrogenation of dicarboxylic acid esters

Abstract Esters of dicarboxylic acids are hydrogenated in the homogeneous phase in the presence of H4Ru4(CO)8(PBu3)4. The corresponding hydroxy esters are the main products from oxalic and malonic esters. Dimethyl succinate gives γ-butyrolactone, while glutaric esters do not react. Only the ortho isomer of the phthalic esters reacts, giving phthalide and methyl benzoate. Both electronic and steric factors affect the course of this reaction.

Homogeneous catalytic hydrogenation of the esters of bicarboxylic acids: Part III. Ethylene glycol from dimethyl oxalate

Abstract Dimethyl oxalate may readily be hydrogenated in the presence of Ru(CO) 2 (CH 3 COO) 2 (PBu 3 ) 2 to methyl glycolate, which is subsequently reduced at a much slower rate to ethylene glycol. The reduction to ethylene glycol is favourably affected by a high hydrogen pressure and the pre-treatment of the catalytic system with a hydroxylated reactant such as methyl glycolate or ethylene glycol itself. The catalytic system under reaction conditions seems to evolve towards less reactive species. Under optimum conditions a 95% conversion of dimethyl oxalate to the corresponding glycol has been achieved.

Selective reduction of dimethyl oxalate by ruthenium carbonyl carboxylates in homogeneous phase Part IV

Abstract Ethylene glycol may be obtained selectively from dimethyl oxalate by hydrogenation in homogeneous phase in the presence of Ru 2 (CO) 4 (CH 3 COO) 2 (P t Pr 3 ) 2 . In order to avoid decomposition of the substrate the hydrogenation must be carried out at 120 °C to completely convert the oxalic diester and then at 180 °C to hydrogenate the intermediate methyl glycolate.

Asymmetric synthesis by chiral ruthenium complexes: XI. Asymmetric hydrogenation of tiglic acid in the presence of phosphine substituted ruthenium carbonyl carboxylates☆

Abstract The enantioface-discriminating hydrogenation of tiglic acid in the presence of (−)-DIOP substituted carbonyl carboxylato complexes of ruthenium has been investigated in order to identify the factors affecting the stereoselectivity of this reaction. The carboxylato ligand present in the catalytic intermediate does not seem to make a significant contribution to the stereoselectivity of this process. The stereoselectivity seems to be associated with the presence of the optically active phosphine. The catalytic system develops during the reaction through intermediates having a higher enantioface-discriminating activity than the initial and the final ruthenium complexes.

Asymmetric synthesis by chiral ruthenium complexes : III. Regioselectivity and asymmetric induction in catalytic hydrogenation of α,β-unsaturated dicarboxylic acids

Abstract The homogeneous catalytic hydrogenation of citraconic and mesaconic acids in the presence of H4Ru4(CO)8[(—)-DIOP]2 gives, in addition to (—)(S)-methylsuccinic acid, a mixture of λ-lactones in ratios which depend on the substrate and the reaction temperature. An exceptionally high regioselectivity is obtained in the hydrogenation at 120°C of the more hindered carboxyl group of mesaconic acid.

Cluster ruthenium hydrogenation catalysts

Abstract Tetraruthenium dodecacarbonyl tetrahydride and some of its phosphine-substituted derivatives have been tested as homogeneous hydrogenation catalysts. The hydrogenation of cyclohexanone in the presence of H 4 Ru 4 (CO) 12 is first order with respect to the catalyst concentration, the substrate concentration and the partial pressure of hydrogen. The ruthenium cluster is recovered unchanged at the end of the reaction.