Enantioselective transition metal catalysis directed by chiral cations

Ye, Xinyi; Tan, Choon‐Hong

doi:10.1039/d0sc05734g

Cited by 32 publications

(18 citation statements)

References 45 publications

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“…Notable exceptions, along with other related examples, have been documented in recent reviews. 11,80 Our group has developed an alternative strategy for uniting privileged chiral cations with transition metals to carry out enantioselective C− H bond functionalization. In this approach, a common achiral ligand scaffold is first rendered anionic through the attachment of a sulfonate group, which can ion-pair with a chiral cation.…”

Section: Transition Metal Catalysismentioning

confidence: 99%

“…There are relatively few examples of combining chiral cations with transition metals, since catalytic cycles rarely contain anionic metal intermediates, precluding direct ion-pairing between a catalytically relevant complex and a chiral cation. Notable exceptions, along with other related examples, have been documented in recent reviews. , Our group has developed an alternative strategy for uniting privileged chiral cations with transition metals to carry out enantioselective C–H bond functionalization. In this approach, a common achiral ligand scaffold is first rendered anionic through the attachment of a sulfonate group, which can ion-pair with a chiral cation.…”

Section: Transition Metal Catalysismentioning

confidence: 99%

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Strategies That Utilize Ion Pairing Interactions to Exert Selectivity Control in the Functionalization of C–H Bonds

2022

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Electrostatic attraction between two groups of opposite charge, typically known as ion-pairing, offers unique opportunities for the design of systems to enable selectivity control in chemical reactions. Catalysis using noncovalent interactions is an established and vibrant research area, but it is noticeable that hydrogen bonding interactions are still the main interaction of choice in system design. Opposite charges experience the powerful force of Coulombic attraction and have the ability to exert fundamental influence on the outcome of reactions that involve charged reagents, intermediates or catalysts. In this Perspective, we will examine how ion-pairing interactions have been used to control selectivity in C–H bond functionalization processes. This broad class of reactions provides an interesting and thought-provoking lens through which to examine the application of ion-pairing design strategies because it is one that encompasses great mechanistic diversity, poses significant selectivity challenges, and perhaps most importantly is of immense interest to synthetic chemists in both industry and academia. We survey reactions that proceed via radical and ionic mechanisms alongside those that involve transition metal catalysis and will deal with control of site-selectivity and enantioselectivity. We anticipate that as this emerging area develops, it will become an ever-more important design strategy for selectivity control.

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Section: Transition Metal Catalysismentioning

confidence: 99%

Section: Transition Metal Catalysismentioning

confidence: 99%

Strategies That Utilize Ion Pairing Interactions to Exert Selectivity Control in the Functionalization of C–H Bonds

2022

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“…Moreover, recently, an alternative to the common metal-plus-chiral-ligand approach has emerged in which chiral transition metal catalysts are assembled exclusively from achiral or optically inactive free ligands with the overall chirality being the consequence of a stereogenic metal center. , This review will only discuss chiral catalysts in which the metal constitutes both the reaction center plus a stereogenic center. Metal-templated catalysis, in which the metal has a purely structural role with the catalysis occurring exclusively through the organic ligand sphere, falls outside the scope of this review. − Furthermore, not covered are chiral metal complex salts in which the chirality originates from the counterion. − …”

Section: Introductionmentioning

confidence: 99%

Metal Stereogenicity in Asymmetric Transition Metal Catalysis

2023

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Chiral transition metal catalysts represent a powerful and economic tool for implementing stereocenters in organic synthesis, with the metal center providing a strong chemical activation upon its interaction with substrates or reagents, while the overall chirality of the metal complex achieves the desired stereoselectivity. Often, the overall chiral topology of the metal complex implements a stereogenic metal center, which is then involved in the origin of the asymmetric induction. This review provides a comprehensive survey of reported chiral transition metal catalysts in which the metal formally constitutes a stereocenter. A stereogenic metal center goes along with an overall chiral topology of the metal complex, regardless of whether the ligands are chiral or achiral. Implications for the catalyst design and mechanism of asymmetric induction are discussed for half-sandwich, tetracoordinated, pentacoordinated, and hexacoordinated chiral transition metal complexes containing a stereogenic metal center. The review distinguishes between chiral metal catalysts originating from the coordination to chiral ligands and those which are solely composed of optically inactive ligands (achiral or rapidly interconverting enantiomers) prior to complexation (dubbed “chiral-at-metal” catalysts).

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“…We recently developed an unconventional approach for the control of enantioselectivity in transition metal catalysis; in comparison to a more traditional strategy in which chirality is embedded within the ligand architecture, ours locates it “off-complex” on a cinchona alkaloid-derived chiral cation, ion-paired with an achiral transition metal complex that has been rendered anionic through the attachment of a sulfonate group (Figure b). − Our first proof-of-concept study achieved asymmetric, desymmetrizing C( sp 2 )–H borylation using iridium catalysis, and we further validated the approach on C( sp 3 )–H amination, wherein a chiral, ion-paired version of Du Bois’ Rh 2 (esp) 2 catalyst mediated selective nitrenoid C–H insertion at a prochiral methylene . We speculated that our ion-paired Rh “Sulfonesp” catalysts developed for that work might also be capable of discriminating between prochiral alkene faces.…”

Section: Introductionmentioning

confidence: 99%

Substrate-Directed Enantioselective Aziridination of Alkenyl Alcohols Controlled by a Chiral Cation

et al. 2023

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Alkene aziridination is a highly versatile transformation for the construction of chiral nitrogen-containing compounds. Inspired by the success of analogous substrate-directed epoxidations, we report an enantioselective aziridination of alkenyl alcohols, which enables asymmetric nitrene transfer to alkenes with varied substitution patterns, including those not covered by the current protocols. We believe that our method is effective because it is substrate-directed, exploiting a network of attractive non-covalent interactions between the substrate, an achiral dianionic rhodium(II,II) tetracarboxylate dimer, and its two associated cinchona alkaloid-derived cations. It is these cations that provide a defined chiral pocket in which the aziridination can occur. In addition to a thorough evaluation of compatible alkene classes, we advance a practical mnemonic to predict reaction outcome and disclose a range of post-functionalization protocols that highlight the unique synthetic potential of the enantioenriched aziridine-alcohol products.

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Enantioselective transition metal catalysis directed by chiral cations

Abstract: Enantioselective transition metal catalysis directed by chiral cations is the amalgamation of chiral cation catalysis and organometallic catalysis.

Cited by 32 publications

References 45 publications

Strategies That Utilize Ion Pairing Interactions to Exert Selectivity Control in the Functionalization of C–H Bonds

Strategies That Utilize Ion Pairing Interactions to Exert Selectivity Control in the Functionalization of C–H Bonds

Metal Stereogenicity in Asymmetric Transition Metal Catalysis

Substrate-Directed Enantioselective Aziridination of Alkenyl Alcohols Controlled by a Chiral Cation

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