The role of functionalized phosphines in the hydrogenation of carboxylic acids in the presence of phosphine substituted hydrido ruthenium complexes

• Published in: Journal of organometallic chemistry 1999-06, Vol.582 (2), p.218-228
• Main Authors: Salvini, Antonella, Frediani, Piero, Bianchi, Mario, Piacenti, Franco, Pistolesi, Leonardo, Rosi, Luca
• Format: Article
• Language: English
• Subjects: Carboxylic acids; Catalytic activity; Functionalized phosphines; Hydrogenation
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/S0022-328X(99)00038-8

Hydrido ruthenium carbonyl complexes substituted by functionalized phosphines such as H 4Ru 4(CO) 8[P(CH 2OCOR) 3] 4 have been synthesized and tested as catalysts in the hydrogenation of carboxylic acids. These complexes are more active than those reported previously, containing trialkyl- or triarylphosphines. On the basis of their behavior, their different activity has been explained in terms of an involvement of the phosphine ligand in the catalytic cycle. The ester group present in the phosphine P(CH 2OCOR) 3 is hydrogenated to produce an alcohol (RCH 2OH) and a P(CH 2OH) group which, in turn, reacts with the free acid present in solution to restore the P(CH 2OCOR) group. This hypothesis has been confirmed by the reactivity of the possible intermediate H 4Ru 4(CO) 8[P(CH 2OH) 3] 4 with acetic acid. Another support to this statement is the almost equal catalytic activity, displayed by H 4Ru 4(CO) 8[P(CH 2OCOR) 3] 4 complexes, whatever the R group present, in the phosphine ligand, in the hydrogenation of carboxylic acids. These complexes, on the other hand, are less active than the corresponding tributylphosphine substituted ones in the hydrogenation of alkenes and ketones. Finally when the phosphine ligand is P(CH 2CH 2COOCH 3) 3 the ester group is not reduced and consequently the catalytic activity of this complex in the hydrogenation of carboxylic acids is very low.