Enantioselective C–C and C–heteroatom bond forming reactions using chiral ferrocene catalysts

Enantioselective Palladium(II)-Catalyzed Desymmetrizative Coupling of 7-Azabenzonorbornadienes with Alkynylanilines

A PdII -catalyzed, domino enantioselective desymmetrizative coupling of 7-azabenzonorbornadienes with alkynylanilines is disclosed herein. This operationally simple transformation generates three covalent bonds and two contiguous stereocenters with excellent enantio- and diastereo-selectivity. The resulting functionalized indole-dihydronaphthalene-amine conjugates served as an appealing platform to streamline the diversity-oriented synthesis (DOS) of other valuable enantioenriched compounds. DFT calculations revealed that the two stabilizing non-covalent interactions contributed to the observed enantioselectivity.

Conceptual advances in nucleophilic organophosphine-promoted transformations

Catalysis by trivalent nucleophilic organophosphines has emerged as an essential tool in organic synthesis. Several new organic transformations promoted by phosphines substantiate and complement the existing synthetic chemistry tools. Mere design of the substrate and reagent combinations has introduced new modes of reactivity patterns, which are otherwise difficult to achieve. These design considerations have led to the rapid build-up of complex molecular entities and laid a solid foundation to synthesise bioactive natural products and pharmaceuticals. This article presents an overview of some of the conceptual advances, including our contributions to nucleophilic organophosphine chemistry. The scope, limitations, mechanistic insights, and applications of these metal-free transformations are discussed elaborately.

Synthesis of Ferrocene 1,3-Derivatives by Distal C-H Activation

The third position of cyclopentadienyl ring of a monosubstituted ferrocene has remained as an inaccessible chemical space for direct functionalization. Until recently, functionalizing the C(3)-position while bypassing the predominantly active C(2)-position is the most challenging task. Herein, we report a distal C-H functionalization of monosubstituted ferrocenes using an easily removable directing group with precise site-selectivity, under a PdII / mono-N-protected amino-acid ligand catalytic system. The robust synthetic protocol leads to the synthesis of ferrocene 1,3-derivatives with broad scope in olefins while functionalizing ferrocenyl methylamine in moderate to good yields via a highly strained ferrocene appended 12-membered palladacycle intermediate.

Introduction of Ferrocene as a Facilitator for the Construction of Supramolecular Polymers

Proper monomer design is the key to enhancing the strength of noncovalent interactions between the molecules toward the efficient formation of supramolecular polymers (SPs). We have designed and synthesized 1,n'-disubstituted ferrocene-azobenzene-long alkyl chains, Fc(CONH-Azo-TDP)₂ , to afford SPs with a high probability. The design exploits the ''molecular ball-bearing'' property of the ferrocene core, which allows two azobenzene arms to rotate in the planes of cyclopentadienyl rings, generating the most suitable molecular conformation required for SP formation. This ferrocene monomer formed a supergel consisting of SPs supported by strong intermolecular (H-bonding and π-π stacking) interactions and higher enthalpy gain than the reference molecules, where the central ferrocene core was replaced by flexible aliphatic as well as rigid benzene linkers. The molecular conformation involved in SPs, the strength of noncovalent interactions, and the process of supramolecular polymerization were investigated through NMR, UV-Vis, XRD and TEM studies. The results demonstrate that ferrocene may act as a good modulator for constructing efficient SPs.

Advanced Application of Planar Chiral Heterocyclic Ferrocenes

This manuscript is reviewing the superior catalytic activity and selectivity of ferrocene ligands in a wide range of reactions: reduction of ketones, hydrogenation of olefins, hydroboration, cycloaddition, enantioselective synthesis of biaryls, Tsuji–Trost allylation. Moreover, the correlation between a ligand structure and its catalytic activity is discussed in this review.

Planar-chiral 1,1'-diaminoferrocenes

Planar-chiral homologues of 1,1'-diaminoferrocene, which bear a single additional substituent adjacent to one of the amino groups, are prepared as racemic mixtures in a few steps and in good yields from ferrocene. Various substituents relevant to steric shielding, coordination and further functionalisation are used, giving access to ferrocene-based planar-chiral diimines and diamines as well as stable N-heterocyclic carbenes and tetrylenes by transformations analogous to procedures established for 1,1'-diaminoferrocene.

Diastereoselective Double C-H Functionalization of Chiral Ferrocenes with Heteroaromatics

Diastereoselective double C-H heteroarylation of chiral ferrocenes provides valuable compounds with multiple functionalities using mild reaction conditions and simple reagents. Pd-Complexes with chiral mono-protected amino acids afforded corresponding heteroarylated ferrocenyl amines in good yields and high diastereomeric purities. In this way, a variety of indole, thiophene, pyrrole, or furan substituents were introduced to the ferrocene moiety. Furthermore, a range of relevant functional groups, for example ketone, ester, chloro, nitro, or silyl, are tolerated by this method. An alternative combination of amino acid and ferrocenyl amine configurations was leveraged to provide the complementary diastereomeric products. The products of C-H heteroarylation can be transformed into corresponding phosphines. Absolute configurations of CH-activation products were confirmed by the combination of X-ray crystallographic analysis and CD spectroscopy. ¹⁹ F NMR kinetic study and DFT calculations provided insights into the reaction mechanism and reasons governing stereoinduction.

Asymmetric Synthesis and Chiroptical Properties of Enantiopure Helical Ferrocenes

An enantiopure helical ferrocene ( R_p)-5 with five ortho-condensed aromatic rings was synthesized using a PtCl₂-catalyzed cycloisomerization of planar-chiral 2-ethynyl-1-(4-phenanthrenyl)ferrocene ( R_p)-6f, prepared in 3 steps from known enantiopure sulfinyl ferrocenyl boronic acid ( S_S, S_p)-7, as the source of planar chirality. This pentacyclic helical ferrocene showed a very high optical rotation value and strong circular dichroism (CD) signals.

Copper-catalyzed synthesis of 2-aminopyridylbenzoxazoles via domino reactions of intermolecular N-arylation and intramolecular O-arylation

A simple and general approach to nitrogen-containing heterocycles via copper-catalyzed domino reaction has been developed, and the corresponding 2-aminopyridylbenzoxazole derivatives were obtained in good to excellent yields using the readily available starting materials. This method possesses unique step economy features, and is of high tolerance towards various functional groups in the substrates.

Planar-Chiral Ferrocene-Based N-Heterocyclic Carbene Ligands

In the last few decades, N-heterocyclic carbene (NHC) ligands, characterized by attractive features, have increased their presence in transition-metal catalysis. However, chiral NHC ligands still require further design enhancement to realize far more exciting synthetic applications. This review documents advances in chiral NHC ligands, focusing on planar-chiral ferrocene-based NHCs. As the basic shape of most classes of NHC rings is planar, it seems rational to employ a planar-chiral element in the design of chiral NHC ligands.

Chiral triazolylidene-Pd-PEPPSI: synthesis, characterization, and application in asymmetric Suzuki–Miyaura cross-coupling

A novel triazolylidene-Pd-PEPPSI with ferrocene-based planar chirality has been synthesized, characterized, and applied to the asymmetric Suzuki–Miyaura cross-coupling.

Stacking of cyclopentadienyl organometallic sandwich and half-sandwich compounds. Strong interactions of sandwiches at large offsets

73% of stacking of Cp sandwiches in the CSD is at large offsets, since these interactions are relatively strong. Much weaker stacking between Cp half-sandwiches is surprising 60% of all stacks, due to more simultaneous interactions.

Intramolecular Direct C-H Arylation via a Metallocenic Radical Pathway: Stereospecific Approach to Planar-Chiral Ferrocenes

Transition metal-free synthesis of planar-chiral 1,2-fused ferrocenes via intramolecular direct C-H bond arylation was achieved. The C-H arylation reactions promoted by a catalytic amount of 1,10-phenanthroline highlighted a unique planar-chiral metallocenic radical intermediate, generated from iodoferrocenes via a single-electron transfer process.

Mild access to planar-chiral ortho-condensed aromatic ferrocenes via gold(i)-catalyzed cycloisomerization of ortho-alkynylaryl ferrocenes

An asymmetric gold(i)-catalyzed intramolecular hydroarylation of aquiral 2-alkynylaryl ferrocenes provides (R_p) planar-chiral ortho-condensed aromatic ferrocenes in high yield and enantioselectivity.

Ferrocene-containing non-interlocked molecular machines

Ferrocene is chemically robust and readily functionalized which enables its facile incorporation into more complex molecular systems. This coupled with ferrocene's reversible redox properties and ability to function as a “molecular ball bearing” has led to the use of ferrocene as a component in wide range of non-interlocked synthetic molecular machine systems.

Ferrocene-based polyethyleneimines for burning rate catalysts

Synthesis, electrochemical behavior, burning rate catalytic performance, and burning rate catalytic and migration mechanism of ferrocene-based polyethyleneimines.

Copper(i) halide clusters based upon ferrocenylchalcogenoether ligands: donors, halides and semi-rigidity effects on the geometry and catalytic activity

Six copper(i) clusters based on ferrocenylchalcogenoethers with different nuclearities and geometries were prepared. Telluroether-based cluster 2 effectively catalyzes the C–N cross-coupling reaction.

Low-migratory ionic ferrocene-based burning rate catalysts with high combustion catalytic efficiency

1-(Ferrocenylmethyl)alkylimidazolium-based ionic compounds with low-migration, high thermal stability and catalytic activity in the thermal degradation of ammonium perchlorate were synthesized and characterized.