22 June 2023
Congratulations to Chen Zhu, Haifeng Chen, Huifeng Yue for the publication in Nature Synthesis!
Keywords: Ni-catalysis, electrochemistry, reductive cross-coupling, difunctionalization
The development of general and efficient strategies for the construction of allenes is important due to their wide applications. Although few protocols have been developed via the 1,4-difunctionalization of 1,3-enynes under thermal or photoredox conditions, the mild and robust methodology for dicarbofunctionalization and hydroalkylation remains unexplored. In the present study, we report an electrochemical multicomponent protocol for the chemo- and regioselective difunctionalization of 1,3-enynes. In particular, 1,4-arylalkylation and unsymmetrical dialkylation have been realized via electro- and nickel dual catalysis using graphite/nickel foam and zinc/nickel foam as electrodes, respectively. The use of a Zn/reticulated vitreous carbon electrode led to efficient 1,4-hydro(deutero)alkylation in the absence of a metal catalyst. A wide range of structurally diverse tri- and tetra-substituted allenes were easily prepared with good efficiency and excellent regioselectivity under mild reaction conditions. Notably, a series of natural product- and drug-derived substrates could undergo late-stage functionalization to generate the corresponding complex allenes.
From February 13-16
2023 the KAUST Research Conference: Advances in Sustainable Catalysis will take place
More information can be found at https://kcc.kaust.edu.sa/2023-conference/home.
1 February 2023
Congratulations to Long Huang, and our collaborators at the Cavallo Lab for the publication in Nature Communications!
Modulating stereoselectivity in allylic C(sp3)-H bond arylations via nickel and photoredox catalysis
Keywords: Ni-catalysis, stereodivergent synthesis, allylic, photoredox catalysis
While significant progress has been made in developing selective C-H bond cross-couplings in the field of radical chemistry, the site and stereoselectivity remain a long-standing challenge. Here, we present the successful development of stereodivergent allylic C(sp3)-H bond arylations through a systematic investigation of the direction and degree of stereoselectivity in the cross-coupling process. In contrast to the signature photosensitized geometrical isomerization of alkenes, the catalytic reaction demonstrates the feasibility of switching the C-C double bond stereoselectivity by means of ligand control as well as steric and electronic effects. Computational studies explain the stereochemical outcome and indicate that excitation of a Ni-allyl complex from singlet to a triplet state results in a spontaneous change of the allyl group coordination and that the subsequent isomerization can be directed by the choice of the ligand to achieve E/Z selectivity.
22 August 2022
Congratulations to Chen and Huifeng for the publication in Angew. Chem. Int. Ed.!
Keywords: Ni-catalysis, photocatalysis, electrocatalysis
The development of methods to access alcohol derivatives is one of the main concerns of considerable research. Herein, a nickel-catalyzed reductive cross-coupling reaction of α-oxy halides is reported with a series of C(sp2)- and C(sp)-electrophiles, including aryl halides, vinyl bromides, alkynyl bromides, and acyl chlorides with the use of a metal reductant, photocatalysis, electrochemistry, and mechanochemistry.
15 August 2022
Congratulations to Haifeng and Chen for the publication in Angew. Chem. Int. Ed.!
Reactivity in Nickel-Catalyzed Multi-component Sequential Reductive Cross-Coupling Reactions
Keywords: Ni-catalysis, multicomponent reaction, reductive cross-coupling
The nickel-catalyzed three-component reductive carbonylation of alkyl halides, aryl halides, and ethyl chloroformate is described. The use of ethyl chloroformate as a safe and readily available source of CO provides an efficient and practical alternative for the synthesis of aryl-alkyl ketones.
29 June 2022
Congratulations to Arunachalam Sagadevan, and our collaborators at the Bakr Lab for the publication in J. Am. Chem. Soc.!
Keywords: Copper nanocluster, C-N bond cross-coupling, photoredox catalysis
Activation of aryl chlorides in cross-coupling reactions is a long-standing challenge in organic synthesis that is of great interest to industry. Ultrasmall (<3 nm), atomically precise nanoclusters (NCs) are considered one of the most promising catalysts due to their high surface area and unsaturated active sites. Herein, we introduce a copper nanocluster-based catalyst, [Cu61(StBu)26S6Cl6H14] (Cu61NC) that enables C–N bond-forming reactions of aryl chlorides under visible-light irradiation at room temperature. A range of N-heterocyclic nucleophiles and electronically and sterically diverse aryl/hetero chlorides react in this new Cu61NC-catalyzed process to afford the C–N coupling products in good yields. Mechanistic studies indicate that a single-electron-transfer (SET) process between the photoexcited Cu61NC complex and aryl halide enables the C–N-arylation reaction.
10 June 2022
Congratulations to Chen and Huifeng for the publication in Nature Communications!
Keywords: Multicomponent reaction, Ni-catalysis, Photocatalysis, Electrochemistry, Photoelectrochemistry
Trisubstituted alkenes are important organic synthons and have broad applications in the synthesis of many pharmaceuticals and materials. The stereoselective synthesis of such compounds has long been a research focus for organic researchers. Herein, we report a three-component, reductive cascade, cross-coupling reaction for the arylalkylation of alkynes. A wide range of trisubstituted alkenes are obtained in good to high yields with excellent chemo- and stereoselectivity by switching between electrochemistry and photocatalysis. The E isomer of the product is obtained exclusively when the reaction is conducted with electricity and nickel, while the Z isomer is generated with high stereoselectivity when photo- and nickel dual catalysts are used. Moreover, photo-assisted electrochemically enabled nickel catalyzed protocol is demonstrated to selectively deliver Z-trisubstituted alkenes without the addition of photocatalysts.
19 May 2022
Congratulations to Jeremy, and our collaborators at the Tung Labs for the publication in Nature Catalysis!
Keywords: Hydride transfer, molybdenum sulfide, H2 evolution, electrocatalysis
Hydride transfers are key to a number of economically and environmentally important reactions, including H2 evolution and NADH regeneration. The electrochemical generation of hydrides can therefore drive the electrification of chemical reactions to improve their sustainability for a green economy. Catalysts containing molybdenum have recently been recognized as among the most promising non-precious catalysts for H2 evolution, but the mechanism by which molybdenum confers this activity remains debated. Here we show the presence of trapped Mo3+ hydride in amorphous molybdenum sulfide (a-MoSx) during the hydrogen evolution reaction and extend its catalytic role to the selective hydrogenation of the biologically important energy carrier NAD to its active 1,4-NADH form. Furthermore, this reactivity applies to other HER-active molybdenum sulfides. Our results demonstrate a direct role for molybdenum in heterogeneous H2 evolution. This mechanistic finding also reveals that molybdenum sulfides have potential as economic electrocatalysts for NADH regeneration in biocatalysis.
18 May 2022
Congratulations to Rajesh, Krishnamoorthy, and our collaborators at the Cavallo and Laquai Labs for the publication in Nature Communications!
Mechanistic insights into photochemical nickel-catalyzed cross-couplings enabled by energy transfer
Keywords: Mechanistic study, Energy transfer, nickel catalysis, photocatalysis
Various methods that use a photocatalyst for electron transfer between an organic substrate and a transition metal catalyst have been established. While triplet sensitization of organic substrates via energy transfer from photocatalysts has been demonstrated, the sensitization of transition metal catalysts is still in its infancy. Here, we describe the selective alkylation of C(sp3)–H bonds via triplet sensitization of nickel catalytic intermediates with a thorough elucidation of its reaction mechanism. Exergonic Dexter energy transfer from an iridium photosensitizer promotes the nickel catalyst to the triplet state, thus enabling C–H functionalization via the release of bromine radical. Computational studies and transient absorption experiments support that the reaction proceeds via the formation of triplet states of the organometallic nickel catalyst by energy transfer.
8 May 2022
Congratulations to Long Huang for the publication in Nature Communications!
Keywords: Cobalt catalysis, PCET, dehydrogenation of alcohol
In the biosynthesis sterols an enzyme-catalyzed demethylation is achieved via a stepwise oxidative transformation of alcohols to olefins. The overall demethylation proceeds through two sequential monooxygenation reactions and a subsequent dehydroformylative saturation. To mimic the desaturation processes observed in nature, we have successfully integrated photoredox proton-coupled electron transfer (PCET) and cobaloxime chemistry for the acceptorless dehydrogenation of alcohols. The state-of-the-art remote and precise desaturation of ketones proceeds efficiently through the activation of cyclic alcohols using bond-dissociation free energy (BDFE) as thermodynamic driving force. The resulting transient alkoxyl radical allows C-C bond scission to generate the carbon-centered radical remote to the carbonyl moiety. This key intermediate is subsequently combined with cobaloxime photochemistry to furnish the alkene. Moreover, the mild protocol can be extended to desaturation of linear alcohols as well as aromatic hydrocarbons. Application to bioactive molecules and natural product derivatives is also presented.
7 July 2022
Congratulations to Rajesh and Krishnamoorthy for the publication in Chemical Science!
Excited-state palladium-catalysed reductive alkylation of imines: scope and mechanism
Keywords: excited palladium catalysis, alkylation, imine
Palladium catalysis induced by visible-light irradiation is a promising tool for promoting unusual chemical transformations. We describe the development of excited-state palladium-catalyzed reductive alkylation of imines with alkyl bromides. The new methodology shows broad functional group tolerance and can additionally be applied in the direct three-component reaction of aldehydes, anilines, and alkyl bromides to give the alkyl amines under mild reaction conditions. Time-resolved photoluminescence experiments allowed the determination of the excited-state reaction kinetics and indicate that the reaction is proceeding via the inner-sphere electron transfer mechanism.
29 Sep 2021
Congratulations to Sam Mathew and Arunachalam Sagadevan for the publication in ACS Catalysis!
One-pot chemoenzymatic conversion of alkynes to chiral amines
Keywords: Biocatalysis, enantioselective catalysis, gold catalysis, chiral amine
A one-pot chemoenzymatic sequential cascade for the synthesis of chiral amines from alkynes was developed. In this integrated approach, just ppm amounts of gold catalysts enabled the conversion of alkynes to ketones (>99%) after which a transaminase was used to catalyze the production of biologically valuable chiral amines in a good yield (up to 99%) and enantiomeric excess (>99%). A preparative scale synthesis of (S)-methylbenzylamine and (S)-4-methoxy-methylbenzylamine from its alkyne form gave a yield of 59 and 92%, respectively, with ee > 99%.