Bromoarene)Mn(CO) 3 þ complexes substituted by methoxy or silyl groups were easily prepared in good to excellent yields, and the molecular structure of [(η 6 -1-bromo-4-methoxybenzene)Mn(CO) 3 ] þ BF 4 has been determined by X-ray crystallography. Nucleophilic additions of LiAlH 4 or PhMgCl delivered the corresponding neutral (η 5 -bromocyclohexadienyl)Mn(CO) 3 complexes. Using ClCO 2 Et and DMF as electrophiles, bromide substitution was achieved by metal-halogen exchange reaction applied to the (η 5 -bromocyclohexadienyl)Mn(CO) 3 complexes and allows the regioselective functionalization of the η 5 -cyclohexadienyl ligand when the two substituents of the starting complex are not adjacent. Furthermore the synthesis of the first (η 5 -cyclohexadienyl)Mn(CO) 3 complexes substituted at one of the extremities of the π-system by a formyl group and the X-ray analysis of one of them emphasized the excellent agreement between the structural and energetic data obtained in the present work and the computed results already reported.

Reaction of hydrides with (η 5 -ketocyclohexadienyl)Mn(CO) 3 complexes yielded the corresponding alcohols as major products but also cyclohexadienes due to the addition of hydride to the C 2 carbon of the C 1 -C 5 π-system. This unexpected regioselectivity has been established by different labeling experiments. The structures of one of the starting keto-substituted (η 5 -cyclohexadienyl)Mn(CO) 3 complexes and its corresponding alcohol have been determined by X-ray crystallography.

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.