Chiral Diphosphine Research Articles

Improved Energy Transfer in the Sensitization of Americium Enables Observation of Circularly Polarized Luminescence

AbstractThe first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and a chiral diphosphine oxide ligand yielded a complex with strong sensitized metal‐centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has often been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of 241Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the 5D1→7F1 transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5 f elements.

Improved Energy Transfer in the Sensitization of Americium Enables Observation of Circularly Polarized Luminescence.

The first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and chiral diphosphine oxide ligands yielded a complex with strong sensitized metal-centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has always been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of 241Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the 5D1 → 7F1 transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5f elements.

Construction of axially chiral 2-arylpyrroles using catalytic asymmetric Suzuki-Miyaura cross-coupling: an efficient approach to esaxerenone.

A general and efficient method has been developed to access axially chiral 2-arylpyrroles using catalytic asymmetric Suzuki-Miyaura cross-coupling. A wide range of axially chiral arylpyrroles were obtained in high yields with good to excellent enantioselectivities. The key to success is the use of a combined catalytic system involving a palladium catalyst and chiral ferrocene diphosphine ligand for achieving effective enantiocontrol. More importantly, this axially chiral CF3-substituted 2-arylpyrrole serves as a key intermediate in the preparation of the anti-hypertensive and diabetic nephropathy drug esaxerenone. It was directly asymmetrically synthesized with high enantioselectivity (92% ee). Thus, a new strategy is provided for the catalytic asymmetric synthesis of esaxerenone.

Highly efficient chiral extraction of amino acid enantiomers using Wei-Phos-Pd as chiral extractant

The development of novel and highly efficient chiral extractants has always been a research hotspot in the field of chiral extraction. In this work, Wei-Phos, an adaptive chiral sulfinamide phosphine ligand featuring multiple coordination centers, was employed as a chiral extractant to separate amino acid enantiomers. The influences of metal precursors, organic solvents, pH of the aqueous phase, extractant concentrations, and extraction temperature on enantioselectivities were investigated. The results show that Wei-Phos-Pd is a highly efficient chiral extractant for amino acid enantiomers. D-amino acids are preferentially recognized by Wei-Phos-Pd. The separation factors for phenylalanine (Phe), homophenylalanine (Hph), 3-chlorophenylglycine (3-Cl-Phg), and 4-nitro-phenylalanine (4-NO2-Phe) are 12.19, 8.89, 13.17 and 7.06, respectively. The structure–activity study and recognition mechanism analysis indicate that the chiral tert-butylsulfinamide group and diphosphine structure in Wei-Phos have significant influences on enantioselectivities. The multiple coordination centers account for the high enantioselectivities of Wei-Phos. Wei-Phos-Pd stands out as the most efficient and versatile chiral diphosphine-metal extractant for chiral extraction of amino acids to date.

Nickel Catalyzed Enantioselective 1,4-Hydroamination of 1,3-Dienes.

Transition metal-catalyzed enantioselective hydroamination of 1,3-dienes provides a direct methodology for the construction of chiral allylamines. So far, all of the reported examples used nucleophilic amines and proceeded with 3,4-regioselectivity. Herein, we describe the first example of nickel-catalyzed enantioselective 1,4-hydroamination of 1,3-dienes using trimethoxysilane and hydroxylamines with a structurally adaptable aromatic spiroketal based chiral diphosphine (SKP) as the ligand, affording a wide array of α-substituted chiral allylamines in high yields with excellent regio- and enantioselectivities. This operationally simple protocol demonstrated a broad substrate scope and excellent functional group compatibility, significantly expanding the chemical space for chiral allylamines. Experimental and DFT studies were performed to elucidate the mechanism and to rationalize the regio- and enantioselectivities of the reaction.

Synthesis of Chiral Vicinal Amino Alcohol Derivatives via Lewis Acid‐Catalyzed Asymmetric Ring Opening of Aziridines with Alcohols and Carboxylic Acids

AbstractUnder the catalysis of a Cu(I) or Ag(I) salt with a chiral diphosphine ligand, the enantioselective nucleophilic ring opening of racemic 2‐styrenylaziridines via kinetic resolution or dynamic kinetic asymmetric transformation (DyKAT) and of meso aziridines via desymmetrization with alcohols was realized. The reaction provided a range of chiral vicinal amino ether derivatives in 47%‐98% yields and with 50%–98% ee. The reaction could be extended to aliphatic carboxylic acids as nucleophiles. The synthetic utility was demonstrated in a four‐step formal synthesis of a diastereomer of the antirythmetic agent vernakalant.

Structures and circularly polarized luminescence of copper(I) complexes with chiral diimine and achiral diphosphine ligands

Abstract Copper(I) complexes with chiral diimine and diphosphine ligands were prepared and their chiroptical properties were investigated. By adding chirality to the diimine ligand, CPL (circularly polarized luminescence) intensities emitted from the copper(I) complex were enhanced to a maximum absolute gem value of 3 × 10−3, which is considered large for a mononuclear copper(I) complex.

Development of a One-Step Synthesis of oxa-Spirocyclic Diphosphine Ligands Driven by Their Application in the Industrial Synthesis of Sacubitril.

Herein we have developed a highly practical and efficient one-step coupling protocol for the synthesis of chiral spiro diphosphine ligands, especially for the oxa-spiro diphosphine ligands O-SDP, which showed excellent reactivity and diastereoselectivity in the asymmetric hydrogenation of a key intermediate of Sacubitril. It should be noted that the one-step coupling protocol could be operated on a kilogram scale, and the resulting ruthenium catalyst of O-SDP could hydrogenate the key intermediate of Sacubitril on an industrial scale.

Iridium-Catalyzed Enantioselective Alkene Hydroalkylation via a Heteroaryl-Directed Enolization-Decarboxylation Sequence.

Upon exposure to a cationic Ir(I)-complex modified with the chiral diphosphine DuanPhos, hydroalkylations of styrenes and α-olefins with diverse heteroaryl tert-butyl acetates occur with complete branched selectivity and very high enantioselectivity. The initial adducts undergo acid promoted decarboxylation in situ to provide alkylated heteroarenes possessing defined β-stereocenters. The processes are postulated to proceed via a stereodefined chiral Ir-enolate, which arises upon heteroarene directed enolization of the heteroaryl acetate precursor. The method can be classified as an enantioselective decarboxylative C(sp3)-C(sp3) cross-coupling.

Design and synthesis of novel 1,3-diene bridged chiral atropoisomeric diphosphine ligands for asymmetric hydrogenation of α-dehydro amino ketones

Design and synthesis of novel 1,3-diene bridged chiral atropoisomeric diphosphine ligands for asymmetric hydrogenation of α-dehydro amino ketones

Cross Couplings of Cinnamates to Benzo‐Fused Oxanorbornadienes

AbstractPotential exo‐specific [3+2] cascade cyclizations between o‐Br‐substituted cinnamates (CM−Br) and benzo‐fused 7‐oxa‐norbornadiene (Bz‐OND) by Pd‐mediated catalysis were explored both in racemic and asymmetric methods. A systematic study on Pd(II) catalysts, silane additives, carbonate bases, solvents, chiral diphosphines within a reaction temperature range of 60–80 °C were carried out. The best combination was between methyl o‐Br‐cinnamate and Bz‐OND catalyzed by Pd(OAc)2/dppf and /DM‐BINAP, respectively, in CH3CN at 80 °C. The desired racemic and optically active Bz‐OND‐fused indanes bearing 1‐carbonylmethylidene (CBM) unit were thus afforded in 95 % and 71 % yields and with enantioselectivities of up to 43 % ee. The optimal asymmetric recipe can be applied to alkyl, aryl cinnamates, 4‐substituted, and 5‐substituted o‐bromo‐cinnamates. Exclusive hydrogenations from the exo‐face of the CBM alkene units can be readily done by Pd(0)/charcoal in EtOAc, affording the product complementary to the direct Rh(I)‐catalyzed cyclization.

Palladium‐Catalyzed Hydroaminocarbonylation of Olefins with Aliphatic Amines without Additives

AbstractPalladium‐catalyzed hydroaminocarbonylation reactions of olefins using aliphatic amines were performed under carbon monoxide atmosphere. Despite the strong basicity of the applied nucleophiles, the targeted amides were successfully synthesized in the absence of acidic additives. Styrene, oct‐1‐ene and isoprene were transformed to the corresponding amide isomers in moderate to good isolated yields under optimized reaction conditions. Various aliphatic amines were used as N‐nucleophiles. The effect of chiral diphosphines on product distribution, that is, on chemo‐, regio‐ and enantioselectivities was also studied. Plausible explanation was given for the additive‐free hydroaminocarbonylation reaction.

Enantioselective Rhodium‐Catalyzed Pauson–Khand Reactions of 1,6‐Chloroenynes with 1,1‐Disubstituted Olefins

AbstractAn enantioselective rhodium(I)‐catalyzed Pauson–Khand reaction (PKR) using 1,6‐chloroenynes that contain challenging 1,1‐disubstituted olefins is described. In contrast to the previous studies with these types of substrates, which are only suitable for a single type of tether and alkyne substituent, the new approach results in a more expansive substrate scope, including carbon and heteroatom tethers with polar and non‐polar substituents on the alkene. DFT calculations provide critical insight into the role of the halide, which pre‐polarizes the alkyne to lower the barrier for metallacycle formation and provides the proper steric profile to promote a favorable enantiodetermining interaction between substrate and chiral diphosphine ligand. Hence, the chloroalkyne enables the efficient and enantioselective PKR with 1,6‐enynes that contain challenging 1,1‐disubstituted olefins, thereby representing a new paradigm for enantioselective reactions involving 1,6‐enynes.

Enantioselective Rhodium-Catalyzed Pauson-Khand Reactions of 1,6-Chloroenynes with 1,1-Disubstituted Olefins.

An enantioselective rhodium(I)-catalyzed Pauson-Khand reaction (PKR) using 1,6-chloroenynes that contain challenging 1,1-disubstituted olefins is described. In contrast to the previous studies with these types of substrates, which is only suitable for a single type of tether and alkyne substituent, the new approach results in a more expansive substrate scope, including carbon and heteroatom tethers with polar and non-polar substituents on the alkene. DFT calculations provide critical insight into the role of the halide, which pre-polarizes the alkyne to lower the barrier for the metallacycle formation and provides the proper steric profile to promote a favorable enantiodetermining interaction between substrate and chiral diphosphine ligand. Hence, the chloroalkyne enables the efficient and enantioselective PKR with 1,6-enynes that contain challenging 1,1-disubstituted olefins, which represents a new paradigm for enantioselective reactions involving 1,6-enynes.

Cationic Rhodium(I)-Catalyzed Asymmetric Cyclohydroformylation of 1,6-Enynes with Formaldehyde.

We report a rhodium(I)-catalyzed asymmetric cyclohydroformylation reaction of 1,6-enynes with formaldehyde. The reaction of 1,6-enynes with formaldehyde in the presence of a cationic Rh(I) catalyst, such as [Rh(cod)2 ]+ OTf- , and a chiral biaryl diphosphine led to asymmetric cyclohydroformylation to produce aldehydes with higher-order structures highly enantioselectively. This transformation procedure is applicable to a variety of enynes, with wide compatibility in various atoms liking between the alkyne and alkene parts, substituents at the alkyne terminus, and substituents at the alkene part, being converted to newly formed aldehydes in 14% to 90% yields with 50% to 98% ee. The products were further transformed with various nucleophiles to alcohols, an amine, and a diene without loss of chirality at their γ-position.

Circularly Polarized Luminescence of Palladium(0) Complexes Bearing Chiral Diphosphines

Four palladium(0) complexes bearing diphosphine ligands were prepared and their chiroptical properties were studied. The structures of two new complexes were elucidated by X-ray crystallography. These complexes show photoluminescence in solution, with quantum yields of 0.4–42%, as well as circular dichroism (CD) at the metal–ligand charge transfer transition bands. The three complexes bearing biaryl phosphine ligands exhibit circularly polarized luminescence of moderate intensities; the sign and the dissymmetry factors of which coincide with the CD spectra.

IrAu12superatom modified by chiral diphosphines: doping-induced enhancement of chiroptical activity

Chiroptical activities of Au13superatom modified with chiral ligands were enhanced by doping of an Ir atom at the center of the core. The IrAu12superatom exhibited the brighter circularly polarized luminescence than Au13superatom.

Steric and dispersion effect of chiral diphosphine ligand on copper-catalyzed enantioselective incorporation of CO2with styrene: a computational study

The π-facial selectivity in 1,2-hydrocuopration step is mainly controlled by ligand–substrate steric repulsion, while stereoselectivity of CO2insertion into the Cu–C bond is primarily determined by ligand–CO2dispersion stabilizing interactions.

Highly efficient and recyclable chiral phosphine-functionalized polyether ionic liquids for asymmetric hydrogenation of β-keto esters.

Herein, based on the concept of integration of phosphine ligands and ionic liquids (ILs), a class of chiral phosphine-functionalized polyether ionic liquids (CPF-PILs) were synthesized by ion-exchange reaction between polyether imidazolium ILs and a phenyl-sulfonated (S)-(-)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) chiral diphosphine ligand, and employed in the Ru-catalyzed homogeneous asymmetric hydrogenation of β-keto esters. The resulting CPF-PILs combined the dual functions of the chiral phosphine ligand and ILs, allowing efficient recovery and recycling of the chiral catalysts using only a catalytic amount of CPF-PILs. The effects of various factors, including the chiral catalyst structure, solvent properties, reaction temperature, hydrogen pressure, and hydrobromic acid dosage, on catalytic performance were thoroughly investigated, as well as the cycling stability and universality of the chiral catalysts were examined. The findings of the present study demonstrated that, under optimal reaction conditions, the model substrate methyl acetoacetate underwent quantitative conversion to methyl β-hydroxybutyrate with a 97% enantiomeric excess (ee). The chiral catalyst used in this process can be recycled up to 12 times and showed good applicability to structurally various β-keto esters. The present study presents a novel approach for using ILs in asymmetric hydrogenation reactions in an environmentally friendly manner.

Structure and Circularly Polarized Luminescence of Copper(I) Complexes Bearing Bipyridine and Chiral Diphosphine Ligands

Copper(I) (Cu(I)) complexes bearing chiral phosphine and diimine ligands were prepared, and their chiroptical properties studied. The complex with a twisted diimine ligand and a diphosphine ligand showed moderate-intensity emission and circularly polarized luminescence (CPL) with considerable dissymmetry factor, gem. The signs and intensities in the CPL spectra were found to reflect the dihedral angles of the two pyridine rings in the diimine ligand.