Cationic Planar Chiral (η6-Arene)Mn(CO)3+ Complexes: Resolution, NMR Study in Chiral-Oriented Solvents, and Applications to the Enantioselective Synthesis of 4-Substituted Cyclohexenones and (η6-Phosphinoarene)Mn(CO)3+ Complexes
journal contributionposted on 13.09.2010, 00:00 by Antoine Eloi, Françoise Rose-Munch, Eric Rose, Ariane Pille, Philippe Lesot, Patrick Herson
An easy round-trip of (D)-(+)-camphor enolate to a racemic mixture of cationic (η6-arene)Mn(CO)3+ complexes is the base of the strategy adopted for the first resolution of such complexes. X-ray structures of one of the (η5-cyclohexadienyl)Mn(CO)3 diastereoisomers obtained after addition of the chiral auxiliary as well as of the corresponding enantiopure η6 cationic complex after rearomatization have been established. Proton-decoupled deuterium 2D NMR in chiral polypeptide liquid crystals proved to be an efficient tool for the determination of the enantiomeric purity of such planar chiral cationic η6 complexes. The potential of this unprecedented resolution is exemplified by enantioselective syntheses in organic and organometallic fields. Thus, starting from the enantiopure (η6-meta-halogenoanisole)Mn(CO)3+ complexes, enantiopure 2,4-disubstituted cyclohexenones were easily generated through a Mn-assisted dearomatization process, and the first examples of enantiopure η5- and η6-phosphino-substituted Mn complexes were obtained through lithiation/electrophilic quench sequence.