Ferrocene enantioselective hydrogenation

Togni and co-workers have used the convergent methodology to link phosphine-containing chiral ferrocene ligands on the cyclophosphazene core to obtain dendrimeric structures of the type 37 (Fig. 21) (201). The reaction with the cyclophosphazene end occurs by the replacement of the P-Cl bond and by the formation of the P-0 bond. The dendrimers contain twelve and sixteen ferrocene moieties respectively. The phosphine units present can coordinate to Rh(I) to afford metallic dendrimers, which have been shown to be excellent catalysts for the enantioselective hydrogenation of dimethyl itaconate. The product... 

Enantioselective Hydrogenation of Alkenes with Ferrocene-Based Ligands... 

Marinetti [53] and Burk [54] reported the preparation of chiral l,l -bis(phos-phetano)ferrocenes (FerroTANE) independently, in which Et-FerroTANE demonstrated excellent enantioselectivity in the rhodium-catalyzed hydrogenation of itaconates. Zhang has reported a l,T-bis(phospholanyl)ferrocene hgand (f-KetalPhos) with ketal substituents at 3,4-positions [55], which proved an excellent ligand for the enantioselective hydrogenation of a-dehydroamino acid derivatives [56]. 

Chen WP, McCormack PJ, Mohammed K, Mbafor W, Roberts SM, Whittall J (2007) Stereoselective synthesis of ferrocene-based c2-symmetric diphosphine ligands application to the highly enantioselective hydrogenation of a-substituted cinnamic acids. Angew Chem Int Ed 46 4141 144... 

Fu has reported a planar-chiral bisphosphorus ligand 45 with a phosphaferrocene backbone. The ligand has provided enantioselectivity up to 96% ee in the hydrogenation of a-dehydroamino acid derivatives.99 Another planar-chiral ferrocene-based bisphosphorus ligand 46 has been reported by Kagan recently and enantioselectivity up to 95% ee has been obtained in the reduction of dimethyl itaconate.100... 

Ferrocene-based complexes have some potential for the enantioselective reduction of ketones, but compared to other ligand classes this is relatively limited [3]. Rh complexes of bppfa, bophoz and josiphos are among the most selective catalysts for the hydrogenation of a-functionalized ketones (Table 25.9 Fig. 25.18, 30-32). Ru complexes of walphos and ferrotane are quite effective for... 

Some excellent bisphosphonite ligands have also been developed. For example, Re-etzfs binaphthol-derived ferrocene-based bisphosphonite hgand L12 has demonstrated to have excellent reactivity and enantioselectivity in the rhodium-catalyzed hydrogenation of itaconates and a-dehydroamino acid derivatives [76]. Zanotti-Gerosa s bisphosphonite ligand L13 has also been successfully apphed to the asymmetric hydrogenation of a-dehydroamino acid derivatives with up to 99% ee [77]. 

Ferrocene-based aminophosphines are shown to be effective ligands in the Ru(II)- catalysed asymmetric hydrogenation of ketones. The enantioselectivity is mainly determined by the C-centred chirality of the ligands, but the planar chirality is also important, and (Rc,SFc)- or (Sc,Rfc)- is the matched combination of chiralities.334 Dimethyl oxalate is selectively hydrogenated to methyl glycolate with Ru(acac)3,... 

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