Chiral Rhodium Complexes Research Articles

Planar Chiral Rhodium Complex Based on the Tetrahydrofluorenyl Core for Enantioselective Catalysis.

A simple four-step route to a chiral tetrahydrofluorenyl rhodium catalyst from naturally occurring (-)-α-pinene was developed. Our approach does not use multistep and time-consuming procedures such as chiral HPLC or diastereomeric resolution. The key to success lies in the face-selective coordination of rhodium to the sterically hindered tetrahydrofluorenyl ligand, giving only one diastereomeric complex. This catalyst proved to be highly efficient for asymmetric C-H annulation of aryl hydroxamates with alkenes (yield up to 95%, 91% ee) at low loading (up to 0.4 mol % based on Rh).

Rh‐catalyzed Asymmetric C(sp3)−H Arylation of 8‐Benzylquinolines with Arylboronic Acids

AbstractRh‐catalyzed asymmetric C(sp3)−H arylation of 8‐benzylquinolines with arylboronic acids was developed. In the presence of 5 mol% BINOL‐derived chiral cyclopentadienyl rhodium complex, asymmetric benzylic C(sp3)−H bond arylation reaction proceeded smoothly to afford a series of enantioenriched triarylmethanes in moderate to good yields with good to excellent enantioselective control (24–89% yields, 63–93% ee). The method displays a broad substrate scope and good functional group tolerance under mild conditions.

Concise Synthesis of Functionalized Cyclopentadienyl Rhodium(III) Complexes via Suzuki–Miyaura Cross Coupling

AbstractHerein, we report a concise method for the preparation of functionalized cyclopentadienyl rhodium complexes via Suzuki–Miyaura cross-coupling. We successfully converted 2,3,4,5-tetramethylcyclopent-2-en-1-one into the corresponding cyclopentadienylboronic acid pinacol ester, which could be used as a coupling partner with aryl halides. Several functionalized cyclopentadienyl rhodium complexes were synthesized in two steps from readily available aryl bromides. We also demonstrated the rapid synthesis of a novel chiral cyclopentadienyl rhodium complex that could be used as a precatalyst for an asymmetric C–H functionalization reaction.

Enantioselective Formation of All-Carbon Quaternary Stereocenters in gem-Difluorinated Cyclopropanes via Rhodium-Catalyzed Stereoablative Kinetic Resolution.

Herein, we report an effective method to offer chiral gem-difluorinated cyclopropanes containing an all-carbon quaternary stereocenter by rhodium-catalyzed stereoablative kinetic resolution. The activation of a sterically hindered all-carbon quaternary C-C bond through oxidative addition with a chiral rhodium complex is proposed as the enantiodetermining step. A wide range of gem-difluorinated cyclopropanes can be obtained with excellent ee values (ee = 87% to >99.9%), which are demonstrated to be useful chiral fluorine-containing building blocks by a series of postfunctionalizations.

Catalytic Enantioselective Synthesis of Functionalized Cyclopropanes from α-Substituted Allyl Sulfones with Donor-Acceptor or Diacceptor Diazo Reagents.

The catalytic asymmetric synthesis of highly functionalized cyclopropanes from α-substituted allyl sulfones and silanes is reported. The reaction, using α-aryl diazoacetates or diacceptor diazo reagents, catalyzed by a chiral rhodium complex (Rh2 ((S)-BTPCP)4 ), furnished the corresponding cyclopropanes in moderate to high yields (27-97 %), high diastereoselectivities (68 : 32 to 20 : 1 d.r.) and moderate to excellent ee (40-99 %). This methodology offers a privileged access to an underexplored class of enantioenriched cyclopropanes with a high level of functionality, an asset for further post-functionalization and their incorporation into more complex structure.

Cover Feature: Planar Chiral Rhodium Complexes of 1,4‐Benzoquinones (Chem. Eur. J. 18/2022)

Chiral rhodium complexes are widely used in asymmetric catalysis. They usually contain intrinsically chiral ligands that provide the desired stereoselectivity. The quinone ligand, just like the playing card in the picture, is planar and thus not chiral. However, upon coordination with rhodium, the symmetry plane is removed, and a chiral complex appears. By using the appropriate auxiliary ligand, or by taking the card with the “right” hand, one can create chiral quinone complexes with exceptional stereoselectivity. More information can be found in the Research Article by N. M. Ankudinov, Yu. V. Nelyubina and D. S. Perekalin (DOI: 10.1002/chem.202200195).

Catalytic Transformations of 2-Pyridones by Rhodium-Mediated Carbene Transfer.

An enantioselective cyclopropanation reaction of N-substituted 2-pyridones with diazo compounds has been realized by using a chiral rhodium complex as the catalyst, and the corresponding chiral cyclopropanes could be formed in good yields with high enantioselectivities. Moreover, using acceptor-acceptor dimethyl 2-diazomalonate as the carbene precursor, a novel 1,4-rearrangement of a Boc group from N to C has also been discovered under rhodium catalysis.

Chiral rhodium(iii)–azobenzene complexes as photoswitchable DNA molecular locks

Two chiral rhodium(iii) complexes with an azobenzene moiety were developed to act as photoswitchable DNA molecular locks, which can photo-regulate DNA transcription in vitro.

Hayashi ligand-based rhodium complex in carbon monoxide and molecular hydrogen-assisted reductive amination

The CO- and H2-assisted reductive amination of carbonyl compounds catalyzed by stable chiral Hayashi ligand-based rhodium complex afforded the racemic amines in moderate yields. The racemic outcome of the process results from the elimination of the chiral ligand from the catalyst under the action of hydrogen or carbon monoxide as reductants.

Oxidation-promoted synthesis of ferrocenyl planar chiral rhodium(iii) complexes for C–H functionalization catalysis

The chemical oxidation of rhodium(i) complexes [Rh(L)(COD)][BF4], where L is a ferrocenyl phosphine/N-heterocyclic carbene ligand, with 2 equiv. of a triaryl-aminium salt [(4-BrC6H4)3N][BF4] in acetonitrile gave planar chiral, air-stable [Rh(L–H)(MeCN)3][BF4]2 complexes where the ferrocene (C5H4CH2ImR or C5H4CH2BImCH2Mes) ring has been C–H activated at the position 2 in good to excellent yields. An important reactivity difference between our complexes and the ubiquitous [Cp*Rh(MeCN)3]X2 complex has been observed in the Grignard-type arylation of 4-nitrobenzaldehyde.

Rhodium‐Catalyzed C−H Activation‐Based Construction of Axially and Centrally Chiral Indenes through Two Discrete Insertions

AbstractReported herein is asymmetric [3+2] annulation of arylnitrones with different classes of alkynes catalyzed by chiral rhodium(III) complexes, with the nitrone acting as an electrophilic directing group. Three classes of chiral indenes/indenones have been effectively constructed, depending on the nature of the substrates. The coupling system features mild reaction conditions, excellent enantioselectivity, and high atom‐economy. In particular, the coupling of N‐benzylnitrones and different classes of sterically hindered alkynes afforded C−C or C−N atropochiral pentatomic biaryls with a C‐centered point‐chirality in excellent enantio‐ and diastereoselectivity (45 examples, average 95.6 % ee). These chiral center and axis are disposed in a distal fashion and they are constructed via two distinct migratory insertions that are stereo‐determining and are under catalyst control.

Nickel-Catalyzed Reductive Asymmetric Aryl-Acylation and Aryl-Carbamoylation of Unactivated Alkenes

Nickel-Catalyzed Reductive Asymmetric Aryl-Acylation and Aryl-Carbamoylation of Unactivated Alkenes

Phospholylmethano P-chirogenic-phosphine-borane as P-(η2-BH3)-chelating ligands of rhodium (I): Synthesis, characterization and asymmetric hydrogenation

The stereoselective synthesis of new phospholylmethano P-chirogenic-phosphine-borane was achieved by P-C bond formation of the bridge, using electrophilic or nucleophilic P*-building blocks. These P1CH2P2*.BH3 ligands behaved as chelating (κ1-P1)-(η2-BH3) entities towards the cationic rhodium(I) centre. The resulting chiral rhodium complexes were tested in asymmetric rhodium catalyzed hydrogenation of methyl 2-(acetamido)acrylate.

Organic Solvent‐free Asymmetric 1,4‐Addition in Liquid‐ or Solid‐State using Conventional Stirring Catalyzed by a Chiral Rhodium Complex Developed as a Homogeneous Catalyst

AbstractOrganic solvent‐free asymmetric 1,4‐addition of arylboronic acids to enone substrates was performed by using a chiral rhodium complex catalyst developed as a homogeneous catalyst. Reactions catalyzed by [RhOH(cod)]2 with chiral diphosphine ligands in liquid‐ or solid‐state proceeded to give chiral 1,4‐adducts in high yield with enantioselectivities up to ca. 100 % ee by conventional stirring without mechanochemistry such as ball milling. The solid‐state reactions under a static condition also proceeded, but with a slight decrease in enantioselectivity of the 1,4‐adduct. SEM observations of the solid‐state reactions indicated that no nanoparticles catalyst was generated. The organic solvent‐free reaction could be applied to gram‐scale synthesis by performing a greener purification using a minimum necessary organic solvent.

Synthesis, Structure, Dynamics, and Enantioface-Selective η3-Benzyl Coordination in the Chiral Rhodium Complexes Rh(diphos*)(η3-CH2Ph)

The rhodium benzyl complexes Rh(diphos*)(η3-CH2Ph) (1–14, diphos* = chiral bis(phosphine)), potential precursors for asymmetric catalysis, were prepared either by treatment of Rh(COD)(η3-CH2Ph) (15...

Chiral Bicyclo[2.2.2]octane‐Fused CpRh Complexes: Synthesis and Potential Use in Asymmetric C−H Activation

AbstractA new class of chiral cyclopentadienyl rhodium(I) complexes (CpRhI) bearing C2‐symmetric chiral bridged‐ring‐fused Cp ligands was prepared. The complexes were successfully applied to the asymmetric C−H activation reaction of N‐methoxybenzamides with quinones, affording a series of chiral hydrophenanthridinones in up to 82 % yield with up to 99 % ee. Interestingly, structure analysis reveals that the side wall of the optimal chiral CpRhI catalyst is vertically more extended, horizontally less extended, and closer to the metal center in comparison with the classic binaphthyl and spirobiindanyl CpRhI complexes, and may thus account for its superior catalytic performance.

Chiral Bicyclo[2.2.2]octane-Fused CpRh Complexes: Synthesis and Potential Use in Asymmetric C-H Activation.

A new class of chiral cyclopentadienyl rhodium(I) complexes (CpRhI ) bearing C2 -symmetric chiral bridged-ring-fused Cp ligands was prepared. The complexes were successfully applied to the asymmetric C-H activation reaction of N-methoxybenzamides with quinones, affording a series of chiral hydrophenanthridinones in up to 82 % yield with up to 99 % ee. Interestingly, structure analysis reveals that the side wall of the optimal chiral CpRhI catalyst is vertically more extended, horizontally less extended, and closer to the metal center in comparison with the classic binaphthyl and spirobiindanyl CpRhI complexes, and may thus account for its superior catalytic performance.

Designing a Planar Chiral Rhodium Indenyl Catalyst for Regio- and Enantioselective Allylic C-H Amidation.

Chiral variants of group IX Cp and Cp* catalysts are well established and catalyze a broad range of reactions with high levels of enantioselectivity. Enantiocontrol in these systems results from ligand design that focuses on appropriate steric blocking. Herein we report the development of a new planar chiral indenyl rhodium complex for enantioselective C-H functionalization catalysis. The ligand design is based on establishing electronic asymmetry in the catalyst, to control enantioselectivity during the reactions. The complex is easily synthesized from commercially available starting materials and is capable of catalyzing the asymmetric allylic C-H amidation of unactivated olefins, delivering a wide range of high-value enantioenriched allylic amide products in good yields with excellent regio- and enantioselectivity. Computational studies suggest that C-H cleavage is rate- and enantio-determining, while reductive C-N coupling from the RhV-nitrenoid intermediate is regio-determining.

Rhodium(I)‐Catalyzed Enantioselective Cyclization of Enynes by Intramolecular Cleavage of the Rh−C Bond by a Tethered Hydroxy Group

AbstractRhodium(I)‐catalyzed enantioselective intramolecular cyclization of enynes having a hydroxy group in the tether was investigated, and various cyclic compounds possessing a chiral quaternary carbon center were obtained in high yields with high ees. In this cyclization, a Rh−C(sp2) bond in the rhodacyclopentene intermediate, which was formed by enantioselective oxidative cycloaddition of enynes to a chiral rhodium(I) complex, was intramolecularly cleaved by σ‐bond metathesis of a tethered O−H bond in the substrate. Furthermore, it was found that the cyclic compounds were obtained with high ees even when the starting materials having a racemic secondary alcohol moiety were used in this reaction.

Rhodium(I)-Catalyzed Enantioselective Cyclization of Enynes by Intramolecular Cleavage of the Rh-C Bond by a Tethered Hydroxy Group.

Rhodium(I)-catalyzed enantioselective intramolecular cyclization of enynes having a hydroxy group in the tether was investigated, and various cyclic compounds possessing a chiral quaternary carbon center were obtained in high yields with high ees. In this cyclization, a Rh-C(sp2 ) bond in the rhodacyclopentene intermediate, which was formed by enantioselective oxidative cycloaddition of enynes to a chiral rhodium(I) complex, was intramolecularly cleaved by σ-bond metathesis of a tethered O-H bond in the substrate. Furthermore, it was found that the cyclic compounds were obtained with high ees even when the starting materials having a racemic secondary alcohol moiety were used in this reaction.