Applications In Enantioselective Catalysis Research Articles

Surfactant Directed Synthesis of Intrinsically Chiral Plasmonic Nanostructures and Precise Tuning of their Optical Activity through Controlled Self‐Assembly

AbstractFabrication and transmission of plasmonic chirality is a rapidly developing area of research. While nanoscale chirality is reasonably well explored, research on intrinsically chiral nanostructures, that has ramifications to origin of homochirality, is still in its infancy. Herein, we report the synthesis of dog‐bone shaped chiral gold nanostructures using a chiral cationic surfactant with excess ascorbic acid. Chiral growth is attributed to the specific binding and structure breaking ability of chiral surfactant and ascorbic acid. The controlled assembly of particles facilitated tuning and enhancement of chiral signals. Experimental observations were validated with theoretical simulations modelled in frequency domain with a surface integral‐equation parameterization. Work highlighting the generation and tuning of plasmonic chirality provides new insights into the understanding of intrinsic chirality and paves way for their application in enantioselective catalysis and biosensing.

Surfactant Directed Synthesis of Intrinsically Chiral Plasmonic Nanostructures and Precise Tuning of their Optical Activity through Controlled Self-Assembly.

Fabrication and transmission of plasmonic chirality is a rapidly developing area of research. While nanoscale chirality is reasonably well explored, research on intrinsically chiral nanostructures, that has ramifications to origin of homochirality, is still in its infancy. Herein, we report the synthesis of dog-bone shaped chiral gold nanostructures using a chiral cationic surfactant with excess ascorbic acid. Chiral growth is attributed to the specific binding and structure breaking ability of chiral surfactant and ascorbic acid. The controlled assembly of particles facilitated tuning and enhancement of chiral signals. Experimental observations were validated with theoretical simulations modelled in frequency domain with a surface integral-equation parameterization. Work highlighting the generation and tuning of plasmonic chirality provides new insights into the understanding of intrinsic chirality and paves way for their application in enantioselective catalysis and biosensing.

Cinchona Alkaloid Catalyzed Dynamic Kinetic Resolution of Biaryl Aldehydes via Asymmetric Decarboxylative Transamination

AbstractAn unprecedented Cinchona alkaloid catalyzed atropoenantioselective transamination of biaryl aldehydes with 2,2-diphenylglycine via a cascade decarboxylation and dynamic kinetic resolution strategy is described. This protocol features broad substrate scope and good functional group tolerance and allows the rapid assembly of axially chiral biaryls in high yields with acceptable to good enantioselectivities. In addition, such structural motifs may have potential applications in enantioselective catalysis as chiral ligands or catalysts.

Controlled Synthesis of Au Chiral Propellers from Seeded Growth of Au Nanoplates for Chiral Differentiation of Biomolecules

Chiral plasmonic nanocrystals are promising materials for applications in enantioselective catalysis, DNA detection, and medical diagnosis. Herein, we demonstrate a simple and versatile strategy th...

Chiral N-heterocyclic Carbene Gold Complexes: Synthesis and Applications in Catalysis

N-Heterocyclic carbenes have found many applications in modern metal catalysis, due to the formation of stable metal complexes, and organocatalysis. Among a myriad of N-heterocyclic carbene metal complexes, gold complexes have gained a lot of attention due to their unique propensity for the activation of carbon-carbon multiple bonds, allowing many useful transformations of alkynes, allenes, and alkenes, inaccessible by other metal complexes. The present review summarizes synthetic efforts towards the preparation of chiral N-heterocyclic gold(I) complexes exhibiting C2 and C1 symmetry, as well as their applications in enantioselective catalysis. Finally, the emerging area of rare gold(III) complexes and their preliminary usage in asymmetric catalysis is also presented.

Ruthenium-Catalyzed Atropoenantioselective Synthesis of Axial Biaryls via Reductive Amination and Dynamic Kinetic Resolution.

The unprecedented ruthenium-catalyzed atropoenantioselective reductive amination of aldehydes with alkylamines via a cascade transfer hydrogenation and dynamic kinetic resolution strategy is described. This protocol features broad substrate scope and good functional group tolerance and allows the rapid assembly of axially chiral biaryls in good to high yields with high to excellent enantioselectivities. In addition, such structural motifs may have potential applications in enantioselective catalysis as chiral ligands or catalysts.

Readily Accessible Unsymmetrical Unsaturated 2,6-Diisopropylphenyl N-Heterocyclic Carbene Ligands. Applications in Enantioselective Catalysis.

A new multicomponent procedure was applied to the synthesis of (a)chiral bulky unsymmetrical unsaturated 2,6-diisopropylphenyl N-heterocyclic carbene (NHC) precursors with excellent selectivity (up to 95%) and good yields. This approach offers access to new chiral NHC ligands, which have found successful applications in both copper-catalyzed asymmetric allylic alkylation and copper-catalyzed asymmetric borylation.

Stereodynamic tetrahydrobiisoindole "NU-BIPHEP(O)"s: functionalization, rotational barriers and non-covalent interactions.

Stereodynamic ligands offer intriguing possibilities in enantioselective catalysis. “NU-BIPHEPs” are a class of stereodynamic diphosphine ligands which are easily accessible via rhodium-catalyzed double [2 + 2 + 2] cycloadditions. This study explores the preparation of differently functionalized “NU-BIPHEP(O)” compounds, the characterization of non-covalent adduct formation and the quantification of enantiomerization barriers. In order to explore the possibilities of functionalization, we studied modifications of the ligand backbone, e.g., with 3,5-dichlorobenzoyl chloride. Diastereomeric adducts with Okamoto-type cellulose derivatives and on-column deracemization were realized on the basis of non-covalent interactions. Enantioselective dynamic HPLC (DHPLC) allowed for the determination of rotational barriers of ΔG‡298K = 92.2 ± 0.3 kJ mol−1 and 99.5 ± 0.1 kJ mol−1 underlining the stereodynamic properties of “NU-BIPHEPs” and “NU-BIPHEP(O)s”, respectively. These results make the preparation of tailor-made functionalized stereodynamic ligands possible and give an outline for possible applications in enantioselective catalysis.

Carbohydrates as enantioinduction components in stereoselective catalysis.

Carbohydrate derivatives are readily available chiral molecules, yet they are infrequently employed as enantioinduction components in stereoselective catalysis. In this review, synthetic approaches to carbohydrate-based ligands and catalysts are outlined, along with example applications in enantioselective catalysis. A wide range of carbohydrate-based functionality is covered, and key trends and future opportunities are identified.

ChemInform Abstract: Ferrocene‐Derived P,N Ligands: Synthesis and Application in Enantioselective Catalysis

Due to their unique steric and electronic properties, air-stability and modular structure, chiral hybrid P,N-ferrocenyl ligands play a prominent role in the field of asymmetric catalysis. This report aims to give a concise introduction to the syntheses of chiral hybrid P,N-ferrocenyl ligands and presents an overview of their application in enantioselective catalysis. This review is of special interest to chemists working on ligand design and asymmetric catalysis, as well as to the broader organic and inorganic community.

Ferrocene-derived P,N ligands: synthesis and application in enantioselective catalysis

Due to their unique steric and electronic properties, air-stability and modular structure, chiral hybrid P,N-ferrocenyl ligands play a prominent role in the field of asymmetric catalysis. This report aims to give a concise introduction to the syntheses of chiral hybrid P,N-ferrocenyl ligands and presents an overview of their application in enantioselective catalysis. This review is of special interest to chemists working on ligand design and asymmetric catalysis, as well as to the broader organic and inorganic community.

Synthesis, characterization and co-ordination chemistry of dioxolanedipyrazoles

The present paper describes a simple access to chiral N,N-donor ligands based on a dioxolane backbone containing two pyrazoles. These ligands can be considered as nitrogen donor analogues to the well established chiral bidentate DIOP ligands which had found wide applications in enantioselective catalysis. The co-ordination chemistry of these ligands is shown exemplarily for palladium(II) and rhodium(I) complexes. All compounds were completely characterized by means of NMR and IR spectroscopy and by elemental analysis. A series of X-ray structural investigations completes the characterization.

ChemInform Abstract: Stereochemistry and Catalysis with Zirconium Complexes

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Immobilization of TADDOL with a High Degree of Loading on Porous Silica Gel and First Applications in Enantioselective Catalysis.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Bis(2-phenylethyl)-nacnac: A Chiral Diketiminate Ligand and Its Copper Complexes

The chiral diketiminate ligand bis-N,N′-(2-phenylethyl)-2,4-diiminopentane, 1H, was synthesized in good yields in a one-step reaction from chiral amine and acetylacetone. Reaction of 1Li(THF) with N-bromosuccinimide yielded the succinimide-substituted ligand 2H. Copper complexes were obtained by reaction of the ligand with a basic copper source in the presence of coordinating Lewis bases, and 1Cu(NCMe), 1Cu(DMAP), 1Cu(PPh3), 1Cu(2,6-xylyl isonitrile), 2Cu(PPh3), and 2Cu(2,6-xylyl isonitrile) have been prepared and, for the most part, characterized by X-ray diffraction studies. Compared to their more common analogues with aromatic substituents on N, 1 and 2 seem to be more basic (1 > 2) and sterically more demanding (2 > 1). Their copper complexes are less stable than those of aryl-substituted diketiminates and tend to decompose by disproportionation, most probably after dissociation of the coordinated Lewis base. Despite the rotational freedom around the N−R* bond, the complexes are sterically rigid, a necessary requirement for potential applications in enantioselective catalysis.

New iridium and rhodium chiral di-N-heterocyclic carbene (NHC) complexes and their application in enantioselective catalysis

New iridium and rhodium complexes prepared from C2-symmetric trans-9,10-dihydro-9,10-ethanoanthracene-11,12-bis(1-R)-benzimidazolidine-2-ylidene ligands (R=Me, iPr, and diPh) have been synthesized and characterized. Their catalytic activities have been tested in enantioselective hydrogenation and hydroformylation reactions. The ee's for the reactions are low. Evidence indicates that even chelating di-N-heterocyclic carbene ligands are susceptible to reductive elimination.

Directed Evolution: An Approach to Engineer Enzymes

ABSTRACTDirected evolution is being used increasingly in industrial and academic laboratories to modify and improve commercially important enzymes. Laboratory evolution is thought to make its biggest contribution in explorations of non-natural functions, by allowing us to distinguish the properties nurtured by evolution. In this review we report the significant advances achieved with respect to the methods of biocatalyst improvement and some critical properties and applications of the modified enzymes. The application of directed evolution has been elaborately demonstrated for protein solubility, stability and catalytic efficiency. Modification of certain enzymes for their application in enantioselective catalysis has also been elucidated. By providing a simple and reliable route to enzyme improvement, directed evolution has emerged as a key technology for enzyme engineering and biocatalysis.

ChemInform Abstract: Synthesis of Optically Active Functionalized Cyclic Ketimines and Their Application in Enantioselective Catalysis.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Immobilization of Chiral Ligands on Polymer Fibers by Electron Beam Induced Grafting and Applications in Enantioselective Catalysis.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The chemistry of chiral heterometallocenes

Chiral heterometallocene derivatives, namely phospha- and azaferrocenes, have recently attracted considerable interest with regard to their stereochemical properties. This perspective summarises recent developments in this field. General synthetic approaches for the construction of various compounds are presented, as well as access to enantiomerically pure material. Reactions that make use of the metallocene-based chirality in subsequent transformations are discussed, including the use as ligands for the stereoselective assembly of metal complexes and applications in enantioselective catalysis.