Tetrathia[7]helicene ([7]TH)-based complexes substituted at the thienyl ring ends by a ferrocenyl group (Fc) or by a (eta(5)-cyclohexadienyl)Mn(CO)(3) derivative have been prepared by Sonogashira coupling reactions starting from the mono- or diiodo [7]TH compounds. The molecular structure of one of the diferrocenyl [7]TH complexes was established by X-ray analysis. Electrochemical investigation on the Fc-[7]TH systems show that the Fc groups are significantly electron poorer with respect to Pc (Delta E degrees approximate to 0.15 V), due to the effective conjugation of the Fc redox moiety with the triple bond + helicene system, as also confirmed by spectroscopic data. Potential cycling around the second oxidation peak, assigned to the thiahelicene moiety, affords fast, regular growth of electrodeposited conducting films, provided that one terminal alpha-thiophene position be available for coupling; on the other hand, long alkyl chains hamper film formation. The conducting films feature a broad oxidation wave resulting from the merging of several redox peaks, having its onset at the Fc oxidation. Since conducting films obtained by electrooligomerization of parent tetrathiahelicene have their onset potentials 0.45 V more positive than the Fc redox sites in this studied Fc-[7]TH conjugates, the above continuity could point to some coupling between Fc redox centers and conjugated pi systems, favored by solid-state stacking.

Mono- and bidentate ligands (5-8, 15-18, 20, 29-31) have been synthesized in which the phosphinyl group substitutes a (eta(5)-cydohexadienyl)Mn(CO)(3) scaffold. In the case of one of the bidentate ligands, 15, the formation of the corresponding Pd complex was studied. The complex unexpectedly afforded two bimetallic complexes depending on the solvent of the reaction: the neutral complex 33 and the cationic complex 34, whose X-ray structures were established. The catalysts carrying the new ligands demonstrated high activity (99% conversion) in the palladium-catalyzed allylic substitution. The resolution of three of the ligands, 6, 8, and 15, was achieved, and the catalyst with the enantioenriched P-N ligand 15 delivered fairly good enantioselectivity in asymmetric allylic substitution.

Ferrocenyl-substituted (eta(5)-hydroxyalkylcyclohexadienyl)-tricarbonylmanganese complexes have been synthesized as well as the corresponding carbenium dinuclear complexes after dehydroxylation. Studies in solution and in the solid state of these zwitterionic species show not only the electronic influence of the positive charge on the eta(5)-Mn complex but also the participation of the two metal atoms in the stabilization of this charge. Catalytic tests show a high activity of these cations as Lewis acids in a typical Diels-Alder reaction.

The synthesis of phosphino derivatives built on a (eta(5)-cyclohexadienyl) Mn(CO)(3) scaffold is efficiently performed using either a lithiation/electrophile quench sequence or a Pd-catalyzed coupling reaction. The structure of one of them was established by X-ray analysis.

Heterobimetallic (di)benzoindenyl Re-Cr complexes have been prepared by a sequence starting from (8-bromobenzo[e]-indenyl)potassium. Reaction with pentacarbonylrhenium bromide affords tricarbonylrhenium complex 2, which has been modified to rhenium-chromium carbene complex 3. Its chromium-templated [3 + 2 + 1]benzannulation afforded the anti(Cr(CO)(3)-Re(CO)(3)) dibenzoindenyl complex 4 as the major product along with the syn diastereoisomer 5. The molecular structures of all heterobimetallic complexes were established by X-ray analyses.

Planar chiral arenetricarbonylchromium complexes have been intensively investigated and they have been applied as valuable building blocks for asymmetric synthesis and as ligands for asymmetric catalysis. In contrast, in the field of the isoelectronic cationic [(η(6)-arene)Mn(CO)(3)](+) complexes, until these last 10 years, very few studies were published involving nonracemic planar chiral cationic complexes and their potential applications, certainly because of the difficult access to enantiopure starting material. In 2009, however, the discovery of the first resolution of such compounds opened a new area for their application in the field of organic as well as of organometallic enantioselective syntheses. We felt it important to write a review on this subject to give an up-to-date summary of the methodologies used to prepare enantiomerically pure planar chiral neutral [(η(5)-cyclohexadienyl)Mn(CO)(3)] and cationic [(η(6)-arene)Mn(CO)(3)](+) complexes as well as their potential in enantioselective synthesis.

An [(eta(6)-1,2,4,5-tetramethylbenzene)Mn(CO)(3)](+) BF4- complex treated with hydride gives a neutral (eta(5)-1,2,4,5-tetramethylcyclohexadienyl)Mn(CO)(3) complex whose X-ray analysis is described. Functionalization of the latter complex at a "benzylic" position using a lithiation/electrophilic quench sequence affords two regioisomers of which the major one corresponds to the functionalization at the C9 carbon. Theoretical computations show that the regioselectivity of lithiation is governed by the stability of the carbanion and thus by its conjugation.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

First Suzuki-Miyaura coupling reactions applied to (η(5)-chloro-cyclohexadienyl)Mn(CO)3 complexes are described and lead to the syntheses of (η(5)-aryl-cyclohexadienyl)Mn(CO)3 and of cationic (η(6)-arene)Mn(CO)3 complexes after rearomatization. The structures of two of the new complexes have been investigated by X-ray diffraction study.

Pentacarbonyl{methoxy-[1-(eta(5)-4-methoxy-6-phenylcyclohexadienyl)tricarbonylmanganese]carbene}chromium (5) accessible from (eta(5)-1-bromo-4-methoxy-6-phenylcyclohexadienyl)tricarbonylmanganese (4) and Cr(CO)(6) undergoes a chromium-templated benzannulation with 3-hexyne to give monometallic Cr complex 12 in 60% yield. The key feature of this reaction is the participation of a conjugated double bond of the eta(5)-cyclohexadienyl-Mn moiety in the [3+2+1] benzannulation reaction. The X-ray structure of complex 12 reveals a syn position of the phenyl group with respect to the Cr tripod, supporting the participation of the Mn moiety in the benzannulation process.

The synthesis of phosphino derivatives built on a (η5-cyclohexadienyl)Mn(CO)3 scaffold is efficiently performed using either a lithiation/electrophile quench sequence or a Pd-catalyzed coupling reaction. The structure of one of them was established by X-ray analysis.

Methoxy(benzo[h]quinolinyl)carbene chromium 2, accessible from benzo[h]quinoline in a two-step protocol, undergoes a chromium-templated benzannulation by 3-hexyne to give (dibenzo[f,h]quinoline)tri...

AbstractThe tricarbonyl‐chromium and ‐manganese groups are known to easily coordinate arene rings to form η6‐arene complexes. The electrophilic nature of the tricarbonyl metal fragments makes the arene electron‐deficient and renders it susceptible to nucleophilic attack. It is for these reasons that a new trend has emerged, the study of the chemistry of (η5‐cyclohexadienyl)Mn(CO)3complexes which are easily obtained by addition of a nucleophile to the arene ring. In the last ten years, the discovery of new methods of functionalization involving Pd cross‐coupling and lithiation reactions has greatly expanded the scope of the (η5‐cyclohexadienyl)Mn(CO)3complexes and consequently represents a key step in the development of the arene manganese chemistry since [(η6‐arene)Mn(CO)3]+complexes can be easily obtained by rearomatization of the corresponding (η5‐cyclohexadienyl)Mn derivatives. The present review aims to describe the situation for the synthesis and the reactivity of η6‐arene‐Mn complexes as well as that of η5‐cyclohexadienyl‐Mn complexes to highlight the recent breakthrough in their chemistry. The main reactivities described for η5Mn complexes correspond to nucleophilic addition, lithiation/electrophilic quench, lithium/halogen exchange and Pd catalyzed reactions. These types of reactions can be efficiently compared with those well studied in η6arenetricarbonylchromium complexes. All these recent developments in the functionalization of η5‐ and η6‐Mn complexes described in this chapter clearly open a revival period for this type of complexes which are starting to emerge as a valuable and versatile class of compounds more environmentally friendly than their Cr analogs.

The tricarbonyl‐chromium and ‐manganese groups are known to easily coordinate arene rings to form η 6 ‐arene complexes. The electrophilic nature of the tricarbonyl metal fragments makes the arene electron‐deficient and renders it susceptible to nucleophilic attack. It is for these reasons that a new trend has emerged, the study of the chemistry of (η 5 ‐cyclohexadienyl)Mn(CO) 3 complexes which are easily obtained by addition of a nucleophile to the arene ring. In the last ten years, the discovery of new methods of functionalization involving Pd cross‐coupling and lithiation reactions has greatly expanded the scope of the (η 5 ‐cyclohexadienyl)Mn(CO) 3 complexes and consequently represents a key step in the development of the arene manganese chemistry since [(η 6 ‐arene)Mn(CO) 3 ] + complexes can be easily obtained by rearomatization of the corresponding (η 5 ‐cyclohexadienyl)Mn derivatives. The present review aims to describe the situation for the synthesis and the reactivity of η 6 ‐arene‐Mn complexes as well as that of η 5 ‐cyclohexadienyl‐Mn complexes to highlight the recent breakthrough in their chemistry. The main reactivities described for η 5 Mn complexes correspond to nucleophilic addition, lithiation/electrophilic quench, lithium/halogen exchange and Pd catalyzed reactions. These types of reactions can be efficiently compared with those well studied in η 6 arenetricarbonylchromium complexes. All these recent developments in the functionalization of η 5 ‐ and η 6 ‐Mn complexes described in this chapter clearly open a revival period for this type of complexes which are starting to emerge as a valuable and versatile class of compounds more environmentally friendly than their Cr analogs.

The synthesis of Cr(CO) 3 -complexed aromatic nitrones 2 is reported. These new planar-chiral complexes were fully characterized in solution by 1 H and 13 C NMR, IR and cyclic voltammetry. Moreover, structural data were obtained from X-ray structures of nitrones 2b, 2d, 2e and 2f. These analyses converge to give evidence of a favoured anti conformation of ortho-substituted nitrones, with an unusual N-O···H aryl intramolecular interaction forming a six-membered ring. The reactivity of these chiral nitrones in SmI 2 -induced pinacol-type reactions was investigated. The reductive cross-coupling of nitrones 2a-d with carbonyl compounds proved to be highly chemo- and diastereoselective and afforded precursors of enantioenriched β-amino alcohols in excellent yields.

An easy round-trip of (D)-(+)-camphor enolate to a racemic mixture of cationic (eta(6)-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 (eta(5)-cyclohexadienyl)Mn(CO)(3) diastereoisomers obtained after addition of the chiral auxiliary as well as of the corresponding enantiopure eta(6) cationic complex after rear-omatization 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 eta(6) complexes. The potential of this unprecedented resolution is exemplified by enantioselective syntheses in organic and organometallic fields. Thus, starting from the enantiopure (eta(6)-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 eta(5)- and eta(6)-phosphino-substituted Mn complexes were obtained through lithiation/electrophilic quench sequence.

[(η6-Pentamethylbenzene)Mn(CO)3]+BF4− 1 and [(η6-1,2,4,5-tetramethylbenzene)Mn(CO)3]+BF4− 2 complexes were prepared and reacted with nucleophiles to provide neutral exo-substituted (η5-polymethylcyclohexadienyl)Mn(CO)3 complexes 3−6. To study the regioselectivity of the deprotonation at a “benzylic” position of (η5-methylcyclohexadienyl)Mn(CO)3 complexes, compounds 3−6 were submitted to a lithiation/electrophilic quench sequence, and functionalized complexes 9−18 were obtained in good yields and with a total regioselectivity. A second sequence gave rise to the formation of unprecedented bifunctionalized (η5-1,2,4,5-tetramethylcyclohexadienyl)Mn(CO)3 and (η5-pentamethylcyclohexadienyl)Mn(CO)3 complexes 19−22.

(eta(5)-1-Hydroxyalkylcyclohexadienyl)tricarbonylmanganese complexes 3a and 3h have been prepared, and their rearomatization delivered compounds 5 and 6, the first benzylic alcohol derivatives coordinated to the cationic Mn(CO)(3) tripod. The structure of 5 has been determined by X-ray crystallography. 1-Hydroxyalkyl 3a, 7, 8, 2-hydroxyalkyl 19, 20, and 3-hydroxyalkyl 25, 26 (eta(5)-cyclohexadienyl)tricarbonylmanganese complexes have been synthesized and studied toward trifluoroacetylation of the hydroxy group when submitted to the action of NEt3 and (CF3CO)(2)O. Only the 2-hydroxyalkyl-substituted complexes eclipsed by a Mn-CO bond of the Mn(CO)(3) tripod gave the expected trifluoroacetate derivatives 21 and 22. For the 1-hydroxyalkyl-substituted complexes, elimination of the trifluoroacetoxy group took place followed by decoordination of the Mn(CO)(3) moiety and trifluoroacetylation, giving rise to trifluoromethyltrienones 10, 11, and 12, whose stuctures were established by X-ray analysis. For 3-hydroxyalkyl-substituted complexes, elimination of the trifluoroticetoxy group also occurred, yielding free arenes 27 and 28 by decoordination of the Mn(CO)(3) entity.

This contribution describes the first resolution of cationic (eta(6)-arene)Mn(CO)(3) complexes through addition of d-(+)-camphor enolate, isomerization of the stereogenic center, and separation and recrystallization of the corresponding eta(5) diastereoisomers followed by rearomatization and elimination of the chiral auxiliary. This general unprecedented chiral nucleophile addition/elimination (eta(6)-eta(5))/(eta(5)-eta(6)) "round trip" sequence uses a cheap, commercially available chiral nucleophile. As it is compatible with the presence of halide and alkoxy groups, a huge number of applications are envisaged. Some of them, such as the synthesis of enantiopure substituted cyclohexenones, are reported in the present work.