Chiral Cobalt Research Articles

A Family of Twisted Chiral Engineered Inorganic Nanoarchitectures.

Chiral inorganic materials possess unique asymmetric properties that could significantly impact various fields. However, their practical application has been hindered by challenges in creating structurally robust chiral materials. We report the synthesis of well-defined chiral-shaped hollow cobalt oxide nanostructures, extendable to a family of chalcogenides including sulfide, selenide, and telluride through topological transformations. Taking chiral cobalt oxide nanostructures as a representative material, we demonstrate precise control over their chiral architectures, enabling fine-tuning of parameters, such as twist degrees, handedness, and compositions. These chiral nanostructures exhibit high spin selectivity effects that influence the electron transfer processes in catalytic reactions. Leveraging this spin-selective behavior, the chiral cobalt oxide nanoarchitectures demonstrate enhanced electrocatalytic performance in the oxygen evolution reaction compared to their achiral counterparts. Our findings not only expand the library of chiral inorganic materials but also advance the application of chiral effects in fields such as catalysis, spintronics, and beyond.

Cobalt-Catalyzed Enantioselective Alkenylation of Aldehydes.

Catalytic enantioselective alkenylation of aldehydes with easily accessible alkenyl halides promoted by a chiral cobalt complex derived from a newly developed tridentate bisoxazolinephosphine is presented. Such processes represent an unprecedented reaction pathway for cobalt catalysis and a general approach that enable rapid construction of highly diversified enantioenriched allylic alcohols containing a 1,1-, 1,2-disubstituted and trisubstituted alkene as well as axial stereogenicity in up to 99 % yield and 99 : 1 er without the need of preformation of alkenyl-metal reagents. DFT calculations revealed the origin of enantioselectivity.

Cobalt‐Catalyzed Enantioselective Alkenylation of Aldehydes

AbstractCatalytic enantioselective alkenylation of aldehydes with easily accessible alkenyl halides promoted by a chiral cobalt complex derived from a newly developed tridentate bisoxazolinephosphine is presented. Such processes represent an unprecedented reaction pathway for cobalt catalysis and a general approach that enable rapid construction of highly diversified enantioenriched allylic alcohols containing a 1,1‐, 1,2‐disubstituted and trisubstituted alkene as well as axial stereogenicity in up to 99 % yield and 99 : 1 er without the need of preformation of alkenyl–metal reagents. DFT calculations revealed the origin of enantioselectivity.

Chiral Transfer and Evolution in Cysteine Induced Cobalt Superstructures.

Chiral organic additives have unveiled the extraordinary capacity to form chiral inorganic superstructures, however, complex hierarchical structures have hindered the understanding of chiral transfer and growth mechanisms. This study introduces a simple hydrothermal synthesis method for constructing chiral cobalt superstructures with cysteine, demonstrating specific recognition of chiral molecules and outstanding electrocatalytic activity. The mild preparation conditions allow in situ tracking of chirality evolution in the chiral cobalt superstructure, offering unprecedented insights into the chiral transfer and amplification mechanism. The resulting superstructures exhibit a universal formation process applicable to other metal oxides, extending the understanding of chiral superstructure evolution. This work contributes not only to the fundamental understanding of chirality in self-assembled structures but also provides a versatile method for designing chiral inorganic nanomaterials with remarkable molecular recognition and electrocatalytic capabilities.

Reversal of enantioselectivity in cobalt(ii)-catalyzed asymmetric Michael–alkylation reactions: synthesis of spiro-cyclopropane-oxindoles

An asymmetric Michael–alkylation reaction with a reversal of enantioselectivity catalyzed by chiral cobalt complexes is reported, giving spiro-cyclopropane-oxindoles with a complete and controlled switch in stereoselectivity (up to 99% and −98% ee).

Cobalt(II)-Catalyzed Enantioselective Propargyl Claisen Rearrangement: Access to Allenyl-Substituted Quaternary β-Ketoesters.

Highly enantioselective propargyl Claisen rearrangement of O-propargyl β-ketoesters was achieved under 2.5 mol % of the chiral cobalt complex as the catalyst under mild reaction conditions. With Co(OTf)2 as the Lewis acid and C1-symmetric imidazoline-pyrroloimidazolone pyridine as the ligand, diverse chiral allenyl-substituted all-carbon quaternary β-ketoesters were obtained in good yields (up to 97% yield) and high enantioselectivities (up to 98% ee).

Asymmetric Epoxidation of Alkenes Catalyzed by a Cobalt Complex.

Asymmetric epoxidation of alkenes catalyzed by nonheme chiral Mn-O and Fe-O catalysts has been well established, but chiral Co-O catalysts for the purpose remain virtually undeveloped due to the oxo wall. Herein is first reported a chiral cobalt complex to realize the enantioselective epoxidation of cyclic and acyclic trisubstituted alkenes by using PhIO as the oxidant in acetone, wherein the tetra-oxygen-based chiral N,N'-dioxide with sterically hindered amide subunits plays a crucial role in supporting the formation of the Co-O intermediate and enantioselective electrophilic oxygen transfer. Mechanistic studies, including HRMS measurements, UV-vis absorption spectroscopy, magnetic susceptibility, as well as DFT calculations, were carried out, confirming the formation of Co-O species as a quartet Co(III)-oxyl tautomer. The mechanism and the origin of enantioselectivity were also elucidated based on control experiments, nonlinear effects, kinetic studies, and DFT calculations.

Asymmetric Catalytic Ring-Expansion of 3-Methyleneazetidines with α-Diazo Pyrazoamides towards Proline-Derivatives.

We realized a highly efficient formal [1,2]-sigmatropic rearrangement of ammonium ylides generated from 3-methylene-azetidines and α-diazo pyrazoamides. The employ of readily available chiral cobalt(II) complex of chiral N,N'-dioxide enabled the ring-expansion of azetidines, affording a variety of quaternary prolineamide derivatives with excellent yield (up to 99 %) and enantioselectivity (up to 99 % ee) under mild reaction condition. For the rearrangement of ammonium ylides, the installation of a pyrazoamide group as a masked brick to build chiral scaffolds proved successful. The enantioselective ring expansion process was elucidated by DFT calculations.

Asymmetric Catalytic Ring‐Expansion of 3‐Methyleneazetidines with α‐Diazo Pyrazoamides towards Proline‐Derivatives

AbstractWe realized a highly efficient formal [1,2]‐sigmatropic rearrangement of ammonium ylides generated from 3‐methylene‐azetidines and α‐diazo pyrazoamides. The employ of readily available chiral cobalt(II) complex of chiral N,N′‐dioxide enabled the ring‐expansion of azetidines, affording a variety of quaternary prolineamide derivatives with excellent yield (up to 99 %) and enantioselectivity (up to 99 % ee) under mild reaction condition. For the rearrangement of ammonium ylides, the installation of a pyrazoamide group as a masked brick to build chiral scaffolds proved successful. The enantioselective ring expansion process was elucidated by DFT calculations.

Histidine-Mediated Synthesis of Chiral Cobalt Oxide Nanoparticles for Enantiomeric Discrimination and Quantification.

Chiral transition metal oxide nanoparticles (CTMOs) are attracting a lot of attention due to their fascinating properties. Nevertheless, elucidatingthe chirality induction mechanism often remains a major challenge. Herein, the synthesis of chiral cobalt oxide nanoparticles mediated by histidine (Co3 O4 @L-His and Co3 O4 @D-His for nanoparticles synthesized in the presence of L- and D-histidine, respectively) is investigated. Interestingly, these CTMOs exhibit remarkable and tunable chiroptical properties. Their analysis by x-ray photoelectron, Fourier transform infrared, and ultraviolet-visibleabsorption spectroscopy indicates that the ratio of Co2+ /Co3+ and their interactions with the imidazole groups of histidine are behind their chiral properties. In addition, the use of chiral Co3 O4 nanoparticles for the development of sensitive, rapid, and enantioselective circular dichroism-based sensors is demonstrated, allowing direct molecular detection and discrimination between cysteine or penicillamine enantiomers. The circular dichroism response of the chiral Co3 O4 exhibits a limit of detection and discrimination of cysteine and penicillamine enantiomers as low as 10µm. Theoretical calculations suggest that the ligand exchange and the coexistence of both species adsorbed on the oxide surface are responsible for the enantiomeric discrimination. This research will enrich the synthetic approaches to obtain CTMOs and enable the extension of the applications and the discovery of new chiroptical properties.

Chiral cobalt(ii) complex-promoted asymmetric para-Claisen rearrangement of allyl α-naphthol ethers

A highly enantioselective para-Claisen rearrangement of allyl α-naphthol ethers is realized by a chiral cobalt(ii)/N,N′-dioxide complex catalyst.

Asymmetric synthesis of complex tricyclo[3.2.2.0]nonenes from racemic norcaradienes: kinetic resolution via Diels-Alder reaction.

Herein, the enantioselective synthesis of complex tricyclo[3.2.2.0]nonenes through the Diels-Alder reaction is reported. Utilizing racemic norcaradienes prepared from the visible-light-mediated dearomative cyclopropanation of m-xylene as dienes and enone derivatives as dienophiles, the overall process represents a kinetic asymmetric transformation in the presence of a chiral cobalt(ii) complex of chiral N,N'-dioxide. High diastereo- and enantioselectivity could be obtained in most cycloaddition processes and part racemization of norcaradiene is observed. The topographic steric maps of the catalysts were collected to rationalize the relationship between reactivity and enantioselectivity with the catalysts.

New anionic cobalt(III) complexes enable enantioselective synthesis of spiro-fused oxazoline and iodoacetal derivatives.

Anionic salicylimine-based cobalt (III) complexes featuring chiral ligands derived from isoleucine amino acids were used as efficient bifunctional phase-transfer catalysts for electrophilic iodination of enol ethers. The Brønsted acids of these complexes enabled the enantioselective asymmetric iodocyclization of enol ethers, furnishing spiro-fused oxazoline derivatives in high yields with up to 90:10 er. In addition, chiral cobalt (III) complexes catalyze the asymmetric intermolecular iodoacetalization of enol ethers with various alcohols to afford 3-iodoacetal derivatives in high yields with up to 92:8 er.

Six-Pointed Star Chiral Cobalt Superstructures with Strong Antibacterial Activity.

Chiral inorganic nanomaterials have shown promise as a potential means of combating bacteria due to their high levels of biocompatibility, easy surface modification, and excellent optical properties. In this study, a diverse range of chiral hierarchical nanomaterials are prepared from Co2+ and L/D-Tartaric acid (Tar) ligands. By combining the ligands in different ratios, chiral Co superstructures (Co SS) are obtained with different morphologies, including chiral nanoflowers, chiral nanohanamaki, a chiral six-pointed star, a chiral fan shape, and a chiral fusiform shape. It is found that the chiral six-pointed star structures exhibit chiroptical activity across a broad range of wavelengths from 300 to 1300nm and that the g-factor is as high as 0.033 with superparamagnetic properties. Under the action of electromagnetic fields, the chiral six-pointed star Co SS shows excellent killing ability against Gram-positive Staphylococcus aureus (ATCC 25923). Compared to L-Co SS, D-Co SS shows stronger levels of antibacterial ability. It is found that the levels of reactive oxygen species generated by D-Co SS are 1.59-fold higher than L-Co SS which is attributed to chiral-induced spin selectivity effects. These findings are of significance for the further development of chiral materials with antibacterial properties.

Front Cover Picture: Insight into the Stereocontrol of DNA Polymerase‐Catalysed Reaction by Chiral Cobalt Complexes (Adv. Synth. Catal. 16/2022)

Front Cover Picture: Insight into the Stereocontrol of DNA Polymerase‐Catalysed Reaction by Chiral Cobalt Complexes (Adv. Synth. Catal. 16/2022)

Insight into the Stereocontrol of DNA Polymerase‐Catalysed Reaction by Chiral Cobalt Complexes

AbstractEnantiomers of chiral substances typically have distinct biological activities, thus, the explorations of biochemical processes at the enantiomeric level has very high significance. This study investigated DNA polymerase–catalyzed reaction modulated by various types of chiral cobalt complexes. The experimental data showed that polymerase reactions were inhibited or accelerated in the presence of K[Co(edta)] ⋅ 2H2O or [Co(en)3]I3 ⋅ H2O. More importantly, the stereocontrol of bioreactivity was found to be different for the enantiomers, which was reflected in their ability to bind to the polymerase reaction system. The docking simulation illustrated that the acceleration or inhibition of polymerase reaction could be correlated with diverse electrostatic energy induced by the attached metal chelates, whereas the different stereocontrol of bioreactivity for the enantiomers was attributed to a discrepancy of Van der Waals interactions between the enantiomer and polymerase catalytic sites.magnified image

Family of Well-Defined Chiral-at-Cobalt(III) Complexes as Metal-Templated Hydrogen-Bond-Donor Catalysts: Effect of Chirality at the Metal Center on the Stereochemical Outcome of the Reaction.

A family of well-defined Λ- and Δ-diastereomeric octahedral cationic chiral-at-cobalt complexes were obtained by a simple two-step reaction of (R,R)-1,2-diaminocyclohexane, (R,R)-1,2-diphenylethylenediamine, or (S)-2-(aminomethyl)pyrrolidine and substituted salicylaldehydes with a cobalt(III) salt. It was observed for the first time that the use of an excess of cobalt(III) salt provides both the enantiopure Λ and Δ forms of the corresponding cobalt(III) complexes 1 and 2 in a ratio of diastereomers ranging from 1:1.6 to >20:1 (Λ/Δ) and in 31-95% combined yields. The obtained complexes were robust, air- and bench-stable, soluble in most of organic solvents, and insoluble in water. Through variation of the substituents in the phenyl ring of the salicylaldehyde moiety, it was shown that both steric and electronic effects of substituents have a significant impact on the formation of Λ and Δ isomers. Next, the efficacies of the enantiopure metal-templated complexes 1-3 were investigated in three benchmark asymmetric reactions in order to compare their catalytic activity. The chiral cobalt(III) complexes 1-3 were tested as enantioselective hydrogen-bond-donor catalysts in such important reactions as the Michael addition of the O'Donnell substrate to methyl acrylate, epoxidation of chalcone, and trimethylsilylcyanation of benzaldehyde. It was clearly demonstrated that the chirality at the cobalt center has an impact on the stereochemical outcome of the reactions. In particular, the Λ(R,R)-1 and Δ(R,R)-1 complexes acted as "pseudoenantiomeric" catalysts in the epoxidation and trimethylsilylcyanoation reactions, providing both enantiomers of the products with up to 57% enantiomeric excess.

Cobalt-Catalyzed Desymmetric Isomerization of Exocyclic Olefins.

Chiral cyclic olefins, 1-methylcyclohexenes, are versatile building blocks for the synthesis of pharmaceuticals and natural products. Despite the prevalence of these structural motifs, the development of efficient synthetic methods remains an unmet challenge. Herein we report a novel desymmetric isomerization of exocyclic olefins using a series of newly designed chiral cobalt catalysts, which enables a straightforward construction of chiral 1-methylcyclohexenes with diversified functionalities. The synthetic utility of this methodology is highlighted by a concise and enantioselective synthesis of a natural product, β-bisabolene. The versatility of the reaction products is further demonstrated by multifarious derivatizations.

A homochiral coordination polymer of cobalt(II) and L-serine.

A one-dimensional chiral cobalt(II) coordination polymer, namely, catena-poly[[[(S)-2-amino-3-hydroxypropanoato-κ2N,O1]cobalt(II)]-μ-(S)-2-amino-3-hydroxypropanoato-κ4O1,O3:N,O1'], [Co(C3H6NO3)2]n or Δ-[Co(L-Ser-κ2N,O)2]n (L-Ser= L-serine) (1), has been synthesized and characterized using elemental and thermal analyses, IR spectroscopy and single-crystal and powder X-ray diffraction techniques. The asymmetric unit of 1 consists of two serine anions which are coordinated to a Co2+ ion to give three chelate rings. These extend the structure into a helical chain with pendant chelate rings which participate in interchain hydrogen bonding. The ability of 1 to undergo transmetallation was evaluated. Among a range of divalent metal ions, only copper(II) partially replaced cobalt(II).

Cobalt-Catalyzed Radical Hydroamination of Alkenes with N-Fluorobenzenesulfonimides.

An efficient and general radical hydroamination of alkenes using Co(salen) as catalyst, N-fluorobenzenesulfonimide (NFSI) and its analogues as both nitrogen source and oxidant was successfully disclosed. A variety of alkenes, including aliphatic alkenes, styrenes, α, β-unsaturated esters, amides, acids, as well as enones, were all compatible to provide desired amination products. Mechanistic experiments suggest that the reaction underwent a metal-hydride-mediated hydrogen atom transfer (HAT) with alkene, followed by a pivotal catalyst controlled SN 2-like pathway between in situ generated organocobalt(IV) species and nitrogen-based nucleophiles. Moreover, by virtue of modified chiral cobalt(II)-salen catalyst, an unprecedented asymmetric version was also achieved with good to excellent level of enantiocontrol. This novel asymmetric radical C-N bond construction opens a new door for the challenging asymmetric radical hydrofunctionalization.