Preparation of Enantiomerically Pure [3]Ferrocenophane‐Based Chelate Bis‐Phosphane Ligands and Their Use in Asymmetric Alternating Carbon Monoxide/Propene Copolymerization

Abstract

An intramolecular Mannich reaction (HNMe₂, TiCl₄) was used to convert 1,1'‐diacetylferrocene to the unsaturated amino[3]ferrocenophane 2. Subsequent hydrogenation gave 3. To obtain enantiomerically pure chelate P,P‐[3]ferrocenophane ligands the readily available pure dimethylamino[3]ferrocenophane enantiomers (R,R)‐3 and (S,S)‐3 each were treated with butyllithium followed by chlorodiphenylphosphane to yield the chelate P,N‐[3]ferrocenophanes (R,R,R_pl)‐10 and (S,S,S_pl)‐10, respectively. Their treatment with HPPh₂ in glacial acetic acid resulted in substitution of the –NMe₂ group by –PPh₂ with overall retention of configuration to yield (R,R,R_pl)‐11 and (S,S,S_pl)‐11, respectively (both characterized by X‐ray diffraction). Similarly, the reaction of (R,R,R_pl)‐10 or (S,S,S_pl)‐10 with dicyclohexylphosphane/HOAc yielded the pure (R,R,R_pl)‐12 and (S,S,S_pl)‐12 enantiomers, respectively. Both these compounds were also characterized by X‐ray crystal structure analyses. (R,R,R_pl)‐12 was employed in catalytic asymmetric hydrogenation and also in asymmetric alternating carbon monoxide/propene copolymerization. A catalyst that was generated in situ from the chelate P,P‐[3]ferrocenophane ligand and palladium acetate gave the CO/propene alternating copolymer with a good activity and high asymmetric induction. The catalyst derived from the reaction of (R,R,R_pl)‐11 with [Rh(cod)₂]BF₄ was employed in the enantioselective hydrogenation of dimethyl itaconate (DMI) (13, ca. 95 % ee, R‐configured product) and methyl α‐acetamidocinnamate (MAC) 14 (ca. 24 % ee, R‐configured product). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)