Unusual Deactivation in the Asymmetric Hydrogenation of Itaconic Acid

Unusual deactivation in the asymmetric hydrogenation of itaconic acid

“…As previously highlighted [3], the hydrogenation kinetics of itaconic acid catalyzed by [Rh(DIPAMP)(MeOH) 2 ]BF 4 is dependent on substrate concentration: reaction rate decreases with increasing substrate concentration under otherwise identical conditions. Fig.…”

“…At room temperature the orange color of the solutions q Part II, for part I see Reference [3]. always fades away within a few minutes, indicating the conversion from complex (1) to the substrate complex (2) (Scheme 1).…”

“…However, when hydrogenation is carried out with the Rh-DIPAMP system we [3] and others [4] observed deactivation of the catalyst. A similar effect was reported when using a rhodium catalyst modified with the Me-DuPhos ligand, thus suggesting that such deactivation might be a common feature of Rh-diphosphane catalysts for this type of substrate [3]. So far the reason for deactivation of the catalyst during hydrogenation of itaconic acid was unknown.…”

“…The same type of complexes is probably formed between itaconic acid and Rh-diphosphane catalysts. However, from a solution of [Rh(DIPAMP)(MeOH) 2 ]BF 4 and itaconic acid we recently isolated an unusual Rh(III) alkyl complex (Scheme 1 (2)) (CCDC-690298) which is formed in a parallel running side reaction [3]. Due to the high stability of the terdentate coordination mode of the substrate to rhodium [7], the metal center is blocked and thus cannot participate in hydrogenation which explains the unusual behavior of the hydrogenation of itaconic acid promoted by the Rh-DIPAMP system [8].…”

Rhodium catalyzed hydrogenation reactions in aqueous micellar systems as green solvents

“…Dimethyl itaconate and itaconic acid are typical test substrates used to study enantioselective hydrogenation reactions. 23,24 Reaction rate and selectivity are compared with the results obtained from methanol as reference. Furthermore a suitable composition of a reaction medium for a continuous process will be formulated among others based on COSMO-RS (a quantum chemistry based a priori method to predict thermophysical data, see chapter 2.2) predictions of partition coefficients of reactants and products.…”