A Graphite Supported Chiral Catalyst

Abstract

Abstract. Partially graphitized carbons were functionalized by carboxylic groups which were esterified with 4-hydroxybenzaldehyde. A chiral diphosphine moiety, analogous to the DIOP framework, was then synthesized from the aldehyde function. The supported chiral diphosphine was transformed into a rhodium catalyst. Preliminary results of asymmetric hydrogenation or asymmetric hydrosilylation are described.

Modification of Carbon Nanofibres for the Immobilization of Metal Complexes: A Case Study with Rhodium and Anthranilic Acid

“…[15±17] Moreover, only few articles have been published regarding the immobilisation of metal complexes on carbon in general. Kagan et al [18] synthesised a chiral rhodium catalyst on partially graphitised carbon, while McCabe and Orchin [19] attached cobalt and tin complexes to bituminous coal. The inertness of CNFs and, to a lesser extent, of carbon in general makes immobilisation with these materials much more difficult than with polymers or oxidic supports, such as silica or alumina.…”

A Pioneering Career in Catalysis: Henri B. Kagan

“…Nevertheless, the enantioinductions obtained clearly demonstrated that graphite functionalized with a chiral diphosphine was developed for the first time. 17 Next to early ligand developments and their applications in asymmetric hydrogenation, the Kagan group studied the mechanism of the Rh-catalyzed reduction of (E,Z)-α-acylaminocinnamic acids 48 with important mechanistic implications and conclusions. The stereochemistry of various α-acylaminocinnamic acids was studied in the presence of the Rh-DIOP complex.…”

“…47 As part as his outstanding discoveries, Professor Kagan, in collaboration with R. Setton, was the first to develop the asymmetric hydrosilylation of ketones by a graphite-supported catalyst with configurations opposite to that observed for the less-enantioselective homogeneous hydrogenation. 47,17 He also carried out unprecedented studies on the Rh-DIOP-catalyzed hydrosilylation of imines, demonstrating that the reactions were at this time more efficient compared to the related ketones, 54 and found that the enantioinductions strongly depended on the nature of the silane used for the transformations. The process proceeded effectively under very mild conditions, generating enormous interest in this method.…”

“…Graphite was the support of choice in such studies, which included graphite bisulfate as a catalyst for Fischer esterification and aromatic nitration, antimony pentachloride-graphite for halogenation reactions, and xenon hexafluoride-graphite for fluorination reactions . After the discovery of 2,3- O -isopropylidene-2,3-dihydroxy-1,4-bis­(diphenylphosphino)­butane (DIOP), Kagan, Setton and co-workers immobilized a DIOP analog on oxidized graphite and studied the performance of the corresponding rhodium catalyst in enantioselective dehydroamino acid- hydrogenation …”

Hydrogenation

“…Thus a relatively rigid support that leads to isolated catalytic sites is the ideal. The latter is suggested by the fact that when diop is supported on graphite, and then treated with [Rh(cod)CI] 2 (reaction (25)) the resulting catalysts give lower optical yields than their homogeneous analogues and more important give products whose absolute configurations are exactly the opposite to those obtained using the corresponding homogeneous catalysts [150]. (24) This interpretation may be correct or it may be simplistic.…”