Palladium-Catalyzed Chloride Substitution of η⁵-(Chlorocyclohexadienyl)Mn(CO)₃Complexes:  An Access to Novel η⁶-(Arene)Mn(CO)₃⁺Cations

Abstract

Functionalization of η5-(chlorocyclohexadienyl)Mn(CO)3 complexes was achieved by palladium-catalyzed reactions using Pd2(dba)3 in the presence of AsPh3. Arylation, carbonylation, and substitution by alkyne-, alkene-, and heteroatom-based nucleophiles were performed, giving rise to functionalized η5 complexes whose structures have been investigated by NMR and X-ray studies. These η5 complexes are valuable precursors upon exo-hydride abstraction, of the corresponding η6 cations, substituted by resonance-withdrawing groups, whose conformations in solution and in the solid state have been studied.

Lithiation/Electrophilic Quench of [(η5‐Cyclohexadienyl)Mn(CO)3]: Versatile Functionalization and Resolution of Planar Chirality in the Organomanganese Series

“…The first cine and tele nucleophilic substitutions of [(η 5 ‐cyclohexadienyl)Mn(CO) 3 ] complexes were developed in 1996 by treatment with hydrides and a proton source,5 and their mechanism was shown to be very close to the cine and tele aromatic nucleophilic substitution (SN Ar ) described for [(η 6 ‐arene)Cr(CO) 3 ] complexes 3d. The discovery of Pd cross‐coupling reactions in the η 5 ‐cyclohexadienyl–Mn series6 enabled ready access to a large variety of substituted η 5 complexes bearing double or triple bonds, aryl, or keto groups linked to the π system. This latter work established that the presence of the tricarbonyl–Mn fragment dramatically activates the carbon–halogen bonds in η 5 ‐cyclohexadienyl–Mn complexes in the same way the tricarbonyl–Cr entity does in η 6 ‐arene–Cr complexes, for which Pd‐catalyzed reactions have been well documented for many years 7.…”

“…Herein, the procedure does not affect the substituents of the starting material, and consequently when a chlorine atom is present, as in 2 , 3 , or 4 , it remains available for subsequent functionalization. This new approach is therefore complementary to the Pd‐catalyzed method developed in this series a few years ago 6. Finally, more strategically important products with wide scope for further transformation were formed by reaction with tributyltin chloride, 1,2‐diiodoethane, or dimethylformamide (DMF; Table 2 entries 4–6, respectively), thus introducing tributylstannyl, iodo, and formyl groups (resulting in complexes 12 – 14 , respectively) adjacent to the methoxy group.…”

“…The [(η 5 ‐cyclohexadienyl)Mn(CO) 3 ] complexes 1 – 4 (Scheme 2) used as starting materials in this study were readily obtained by nucleophilic addition of PhMgCl onto the corresponding [(η 6 ‐arene)Mn(CO) 3 ] + complexes 6. 8 Chloro‐ and/or methoxy‐substituted arenes were used for their good ortho ‐directing properties in the lithiation step,9 either as a result of an inductive electron‐withdrawing effect (Cl) or a lithium coordination (OMe) 2d…”

“…These results show that the reaction is efficient for the introduction of alkyl, benzylic alcohol, and ester groups (Table 2, entries 1–3, respectively). It should be pointed out that we also introduced ester groups into [(η 5 ‐chlorocyclohexadienyl)Mn(CO) 3 ] complexes by using the CCl reactivity towards Pd‐catalyzed coupling reactions under a CO atmosphere 6. Herein, the procedure does not affect the substituents of the starting material, and consequently when a chlorine atom is present, as in 2 , 3 , or 4 , it remains available for subsequent functionalization.…”

Réactivité des complexes (η5-cyclohexadiényl)Mn(CO)3 substitués par des groupes électroattracteurs vis-à-vis d'hydrures

“…Ce complexe est préparé conformément à la procédure dével-oppée au laboratoire [6]. Après addition de LiAlH 4 sur le complexe cationique 4, le complexe 5 se forme avec 54% de rendement correspondant à l'attaque régiosé-lective de l'hydrure en ortho du chlore (Schéma 3) [5a].…”