Cooperative Catalytic System Research Articles

Dynamic Asymmetric Diamination of Allylic Alcohols through Borrowing Hydrogen Catalysis: Diastereo-Divergent Synthesis of Tetrahydrobenzodiazepines.

We present herein a catalytic enantioconvergent diamination of racemic allylic alcohols with the construction of two C-N bonds and 1,3-nonadjacent stereocenters. This iridium/chiral phosphoric acid cooperative catalytic system operates through an atom-economical borrowing hydrogen amination/aza-Michael cascade, and converts readily available phenylenediamines and racemic allylic alcohols to 1,5-tetrahydrobenzodiazepines in high enantioselectivity. An intriguing solvent-dependent switch of diastereoselectivity was also observed. Mechanistic studies suggested a dynamic kinetic resolution process involving racemization through a reversible Michael addition, making the last step of asymmetric imine reduction the enantiodetermining step of this cascade process.

Unveiling Non-Covalent Interactions in Novel Cooperative Photoredox Systems for Efficient Alkene Oxidation in Water.

A new cooperative photoredox catalytic system, [RuII(trpy)(bpy)(H2O)][3,3'-Co(8,9,12-Cl3-1,2-C2B9H8)2]2, 5, has been synthesized and fully characterized for the first time. In this system, the photoredox catalyst [3,3'-Co(8,9,12-Cl3-1,2-C2B9H8)2]-[Cl6-1]-, a metallacarborane, and the oxidation catalyst [RuII(trpy)(bpy)(H2O)]2+, 2 are linked by non-covalent interactions. This compound, along with the one previously synthesized by us, [RuII(trpy)(bpy)(H2O)][(3,3'-Co(1,2-C2B9H11)2]2, 4, are the only examples of cooperative molecular photocatalysts in which the catalyst and photosensitizer are not linked by covalent bonds. Both cooperative systems have proven to be efficient photocatalysts for the oxidation of alkenes in water through Proton Coupled Electron Transfer processes (PCETs). Using 0.05 mol% of catalyst 4, total conversion values were achieved after 15 min with moderate selectivity for the corresponding epoxides, which decreases with reaction time, along with the TON values. However, with 0.005 mol% of catalyst, the conversion values are lower, but the selectivity and TON values are higher. This occurs simultaneously with an increase in the amount of the corresponding diol for most of the substrates studied. Photocatalyst 4 acts as a photocatalyst in both the epoxidation of alkenes and their hydroxylation in aqueous medium. The hybrid system 5 shows generally higher conversion values at low loads compared to those obtained with 4 for most of the substrates studied. However, the selectivity values for the corresponding epoxides are lower even after 15 min of reaction. This is likely due to the enhanced oxidizing capacity of CoIV in catalyst 5, resulting from the presence of more electron-withdrawing substituents on the metallacarborane platform.

Effect of zeolites on the alkylation of aromatics with alkanes using a Pd nanoparticle/solid acid cooperative catalytic system

The direct alkylation of benzene with alkanes is an effective method for alkylbenzene production. Our group previously discovered that a mixture of supported Pd nanoparticles and solid acids effectively promoted the alkylation of benzene with alkanes. Herein, the alkylation of toluene with n-heptane was catalyzed by physical mixture of H-mordenite and Pd nanoparticles supported on hydrotalcite to afford the corresponding C7 alkylation product with 87% selectivity and 14% toluene conversion. The reaction slightly proceeded in the absence of Pd nanoparticles or H-mordenite, indicating cooperative catalysis by the two different solid catalysts. Moreover, the high stability of the Pd nanoparticles on hydrotalcite was confirmed via reuse experiments and transmission electron microscopy (TEM) analysis. The catalyst mixture was reused at least three times without any loss of product yield, and after three reuses, TEM analysis revealed that the size of the Pd nanoparticles following the initial catalytic reaction was similar to that of the catalyst. Scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS) analysis of the recovered catalyst mixture revealed the preservation of Pd nanoparticles on the hydrotalcite surface, as well as the close positioning of the two different catalyst particles, thus suggesting interparticle hydrogen transfer. The structure of the solid acid strongly affected the alkylation product selectivity. For example, H-mordenite showed high selectivity for the n-heptane alkylation product with a C7 alkyl chain, whereas the selectivity changed with other zeolites. This cooperative catalytic system can be applied to the alkylation of other substituted benzenes, such as xylenes and phenols, with good selectivity toward the desired alkylation product.

Organocatalytic Asymmetric Cascade Michael-Acyl Transfer Reaction between 2-Fluoro-1,3-diketones and 2-Hydroxynitrostyrenes.

An organocatalytic asymmetric cascade Michael-acyl transfer reaction of 2-hydroxynitrostyrenes and monofluorinated β-diketones has been developed employing a cooperative catalytic system. A combination of quinine-derived bifunctional squaramide catalyst and achiral hydrogen bond donor cocatalyst was found to be the most effective for this reaction and provided the fluorinated acyl transfer products in high yields with good diastereo- and excellent enantioselectivities. Synthetic transformations have been demonstrated, including the synthesis of functionalized 2,3-dihydrobenzofurans and 1-pyrroline.

Computational design of cooperatively acting molecular catalyst systems: carbene based tungsten- or molybdenum-catalysts with rhodium- or iridium-complexes for the ionic hydrogenation of N2 to NH3.

This density functional theory (DFT) study explores the efficacy of cooperative catalytic systems in enabling the ionic hydrogenation of N2 with H2, leading to NH3 formation. A set of N-heterocyclic carbene-based pincer tungsten/molybdenum metal complexes of the form [(PCP)M1(H)2] (M1 = W/Mo) were chosen to bind N2 at the respective metal centres. Simultaneously, cationic rhodium/iridium complexes of type [Cp*M2{2-(2-pyridyl)phenyl}(CH3CN)]+ (Cp* = C5(CH3)5 and M2 = Rh/Ir), are employed as cooperative coordination partners for heterolytic H2 splitting. The stepwise transfer of protons and hydrides to the bound N2 and intermediate NxHy units results in the formation of NH3. Interestingly, the calculated results reveal an encouraging low range of energy spans ranging from ∼30 to 42 kcal mol-1 depending on different combinations of ligands and metal complexes. The optimal combination of pincer ligand and metal center allowed for an energy span of unprecedented 29.7 kcal mol-1 demonstrating significant potential for molecular catalysts for the N2/H2 reaction system. While exploring obvious potential off-cycle reactions leading to catalyst deactivation, the computed results indicate that no increase in energy span would need to be expected.

Dual Photoredox/Nickel-Catalyzed Dehydrative Difluoroalkylation of Benzyl Alcohols for the Synthesis of Allylic gem-Difluorides.

A photoredox/Lewis acid cooperative catalytic system has been developed for the construction of Cvinyl-CRf bonds through the dehydrative difluoroalkylation of benzyl alcohols. A variety of allylic gem-difluorides could be obtained in moderate yields with good to excellent E/Z selectivity. In addition, several control experiments have been explored, and a possible mechanism was proposed for this process.

Asymmetric [3 + 2] Photocycloaddition of β-Keto Esters and Vinyl Azides by Dual Photoredox/Nickel Catalysis.

Photocatalytic [3 + 2] cycloadditions and control of stereochemistry have remained a substantial challenge, particularly in the context of heterocycle synthesis; sporadic successful examples have involved enantioselective [3 + 2] photocycloaddition between redox-active direct group-containing cyclopropanes and alkenes for creation of cyclopentanes. Herein, we report a cooperative catalytic system comprising a chiral nickel Lewis acid catalyst and an organic photocatalyst fueled by visible-light irradiation that allows for the hitherto elusive asymmetric [3 + 2] photocycloaddition of β-keto esters with vinyl azides under redox-neutral conditions. This protocol enables highly enantioselective construction of polycyclic densely substituted 3,4-dihydro-2H-pyrrole heterocycles featuring two contiguous tetrasubstituted carbon stereocenters, including a useful chiral N,O-ketal motif that is not easily accessible with other catalytic methods. Mechanistic studies revealed that the overall reactivity relies on the seamless integration of dual roles of nickel catalysts by the catalytic formation of the substrate/Ni complex, assisting both photoredox event and enantioselective radical addition.

An Iridium/Aluminum Cooperative Strategy for the β‐C(sp3)‐H Borylation of Saturated Cyclic Amines

AbstractDespite the widespread success in the functionalization of C(sp2)−H bonds, the deliberate functionalization of C(sp3)−H bonds in a highly site‐ and stereoselective manner remains a longstanding challenge. Herein, we report an iridium/aluminum cooperative catalytic system that enables the β‐selective C−H borylation of saturated cyclic amines and lactams. Furthermore, we have accomplished an enantioselective variant using binaphthol‐derived chiral aluminum catalysts to forge C−B bonds with high levels of stereocontrol. Computational studies suggest that the formation of a Lewis pair with the substrates is crucial to lower the energy of the transition state for the rate‐determining reductive elimination step.

Photocatalytic enantioselective Minisci reaction of β-carbolines and application to natural product synthesis.

A highly efficient enantioselective direct C-H functionalization of β-carbolines via a Minisci-type radical process under a photo-redox and chiral phosphoric acid cooperative catalytic system has been disclosed. Through this protocol, a wide range of C1 aminoalkylated β-carbolines were constructed directly with high levels of enantioselectivities from readily available β-carbolines and alanine-derived redox-active esters. This transformation allows straightforward access to highly valuable enantioenriched β-carbolines, which are an intriguing structural motif in valuable natural products and synthetic bio-active compounds. This protocol has been utilized as a highly efficient synthetic strategy for the concise asymmetric total synthesis of marine alkaloids eudistomin X, (+)-eudistomidin B and (+)-eudistomidin I.

Arene Hydrogenation by Cooperative Catalytic Systems of Metal Nanoparticles and Lewis Acids

Key words rhodium catalysis - platinum catalysis - bimetallic catalysis - nanoparticles - Lewis acids - hydrogenation

Bottlebrush polymeric catalyst: Boosting activity for CO2/epoxide copolymerization

A dynamic multi-cooperative strategy of constructing bottlebrush catalysts for the ring-opening copolymerization of carbon dioxide and propylene epoxide was developed. Nine bottlebrush polymeric aluminum porphyrin catalysts (BPAPC) were prepared through regulation of both brush length and bristle length, affording enhanced catalytic performances. Among them, BPAPC 5 with optimized topology exhibited a high activity (turnover frequency = 8,110 h−1) for the copolymerization of carbon dioxide and propylene epoxide, while maintaining high polymer selectivity of 99% at 110 °C. Notably, BPAPC 5 even could achieve a high turnover number of 39,000 at a very low catalyst loading ([PO]/[Al] = 50,000), yielding the copolymer with a number-average molecular weight of 271 kg∙mol−1. Moreover, through customizable catalyst design by manipulating steric confinement and ligand chemistry environment, the carbonate unit content of resulting polymers can be adjusted in the range of 35%–75%. Furthermore, the established balloon chain model explained the structure–function relationships of BPAPCs. This study provides a general design guide for cooperative catalytic systems.

Cooperative catalytic Prins cyclization for the construction of azaspiro[5.5]undec-2-ene frameworks

Homoallylic alcohols appended with N-propargyl moiety undergo a smooth condensation with aldehydes in the presence of 5 mol% of Ph3PAuCl/AgSbF6/In(OTf)3 catalytic system in dichloromethane at 25 °C to afford the corresponding 1,9-dioxa-4-azaspiro[5.5]undec-2-ene scaffolds in good yields. This is the first report on the synthesis of azaspiro[5.5]undec-2-enes using a cooperative catalytic system.

Synthesis of Optically Active syn- and anti-Chlorohydrins through a Bienzymatic Reductive Cascade.

A bienzymatic cascade has been designed and optimized to obtain enantiopure chlorohydrins starting from the corresponding 1-aryl-2-chlorobut-2-en-1-ones. For the synthesis of these α-chloroenones, a two-step sequence was developed consisting of the allylation of the corresponding aldehyde with 3-dichloroprop-1-ene, followed by oxidation and further isomerization. The selective cooperative catalytic system involving ene-reductases (EREDs) and alcohol dehydrogenases (ADHs) afforded the desired optically active chlorohydrins under mild reaction conditions in excellent conversions (up to >99%) and selectivities (up to >99:1 diastereomeric ratio (dr), >99% enantiomeric excess (ee)).

Complementary Cooperative Catalytic Systems in the Aerobic Oxidation of a Wide Range of Si−H‐Reagents to Si−OH‐Products: From Monomers to Oligomers and Polymers

AbstractThe article presents an in‐depth study of the applicability of cooperative [M]‐/Organo‐catalytic systems in aerobic Si−H‐functionalization. A thorough kinetic study allowed us to identify two “complementary” catalytic systems based on earth‐abundant [M]‐catalysts and inexpensive commercially available organic catalysts. The first system, Co(OAc)2/N‐hydroxysuccinimide, made it possible to oxidize a Si−H‐group to a Si−OH‐group in a wide range of monomers, including previously unknown ones, that dramatically differ in their reactivity. However, this system failed in the case of oligomeric and polymeric substrates. This problem was solved by application of the Cu(OAc)2/N‐hydroxyphthalimide system. A wide potential for gram‐scale (50–100 g) preparation of Si−OH‐containing products with molecular architectures of different complexity was revealed using the established “substrate‐reactivity‐catalytic system” relationship. In particular, previously unknown types of dumbbell‐shaped and graft polymers were synthesized using alkoxysilanols.

Supported Pt Enabled Proton-Driven NAD(P)+ Regeneration for Biocatalytic Oxidation.

The utilization of biocatalytic oxidations has evolved from the niche applications of the early 21st century to a widely recognized tool for general chemical synthesis. One of the major drawbacks that hinders commercialization is the dependence on expensive nicotinamide adenine dinucleotide (NAD(P)+) cofactors, and so, their regeneration is essential. Here, we report the design of carbon-supported Pt catalysts that can regenerate NAD(P)+ by proton-driven NAD(P)H oxidation with concurrent hydrogen formation. The carbon support was modified to tune the electronic nature of the Pt nanoparticles, and it was found that the best catalyst for NAD(P)+ regeneration (TOF = 581 h-1) was electron-rich Pt on carbon. Finally, the heterogeneous Pt catalyst was applied in the biocatalytic oxidation of a variety of alcohols catalyzed by different alcohol dehydrogenases. The Pt catalyst exhibited good compatibility with the biocatalytic system. Its NAD(P)+ regeneration function successfully supported biocatalytic conversion from alcohols to corresponding ketone or lactone products. This work provides a promising strategy for chemical synthesis via NAD(P)+-dependent pathways utilizing a cooperative inorganic-enzymatic catalytic system.

Reaction Rate Acceleration of Cooperative Catalytic Systems: Metal Nanoparticles and Lewis Acids in Arene Hydrogenation.

Employing two distinct catalysts in one reaction medium synergistically is a powerful strategy for activating less reactive substrates. Although the approach has been well-developed in homogeneous conditions, it remains challenging and rare in heterogeneous catalysis, especially under gas-liquid-solid multiphase reaction conditions. Here, we describe the development of cooperative and synergistic catalyst systems of heterogeneous Rh-Pt bimetallic nanoparticle catalysts, Rh-Pt/DMPSi-Al2 O3 , and Sc(OTf)3 in the liquid phase for the hydrogenation of arenes under very mild conditions. Dramatic rate acceleration was achieved with cooperative activation. Remarkably, more challenging substrates that contained strong electron-donating groups and sterically hindered substituents were smoothly hydrogenated. Mechanistic insights into the cooperative activation of an aromatic substrate by heterogeneous metal nanoparticles and a soluble Lewis acid was obtained by kinetic studies and by direct observation of 1 H and 45 Sc NMR spectra.

Reaction Rate Acceleration of Cooperative Catalytic Systems: Metal Nanoparticles and Lewis Acids in Arene Hydrogenation

AbstractEmploying two distinct catalysts in one reaction medium synergistically is a powerful strategy for activating less reactive substrates. Although the approach has been well‐developed in homogeneous conditions, it remains challenging and rare in heterogeneous catalysis, especially under gas‐liquid‐solid multiphase reaction conditions. Here, we describe the development of cooperative and synergistic catalyst systems of heterogeneous Rh‐Pt bimetallic nanoparticle catalysts, Rh‐Pt/DMPSi‐Al2O3, and Sc(OTf)3 in the liquid phase for the hydrogenation of arenes under very mild conditions. Dramatic rate acceleration was achieved with cooperative activation. Remarkably, more challenging substrates that contained strong electron‐donating groups and sterically hindered substituents were smoothly hydrogenated. Mechanistic insights into the cooperative activation of an aromatic substrate by heterogeneous metal nanoparticles and a soluble Lewis acid was obtained by kinetic studies and by direct observation of 1H and 45Sc NMR spectra.

Photocatalytic materials for sustainable chemistry via cooperative photoredox catalysis

Utilizing photocatalytic technology to reduce water or carbon dioxide to solar fuels and to selectively or non-selectively oxidize organics to their respective target products, is a promising and sustainable way to increase the supply of energy and chemical feedstocks, reduce greenhouse gas emissions, and solve environmental pollution. However, photoredox reaction proceeding efficiently and stably is often a challenge in the absence of scavengers. A recent development surge is integrating solar fuels production and organic oxidation into a light-driven photoredox system, so as to realize the simultaneous utilization of electrons and holes, which is desirable from the consideration of economic benefits of photocatalytic technology application. In this review, we briefly recap the recent advances concerning dual-function cooperative photoredox catalytic systems integrating solar fuels production with organic oxidation. Firstly, the dual-functional reaction systems combining hydrogen production and organic oxidation are discussed, which includes hydrogen evolution coupled with non-selective organic oxidation to degrade pollutants, and hydrogen evolution integrated with selective organic conversion to produce value-added chemicals. After that, we discuss the emerging system combining carbon dioxide reduction and organic conversion. Finally, we cast a personal prospect on the opportunities and challenges for the future development of this booming and cooperative dual-function photoredox catalysis field.

Achiral Cp*Rh(III)/Chiral Lewis Base Cooperative Catalysis for Enantioselective Cyclization via C-H Activation.

An enantioselective [4+3] cyclization via C(sp2)-H activation with a cooperative catalytic system consisting of a Cp*Rh(III) complex and a chiral Lewis base is described. An α,β-unsaturated acyl ammonium intermediate is generated from a chiral isochalcogenurea catalyst and an acyl fluoride reacts with a metallacycle generated from the Cp*Rh catalyst and a benzylamine derivative. This cooperative catalytic system gives a variety of benzolactams in good yields with excellent enantioselectivities (up to 99:1 er). The results demonstrated that chiral Lewis base catalysis is a powerful tool for controlling the enantioselectivity of transition metal-catalyzed C-H functionalizations.

Asymmetric Azide-Alkyne Cycloaddition with Ir(I)/Squaramide Cooperative Catalysis: Atroposelective Synthesis of Axially Chiral Aryltriazoles.

An Ir(I)/squaramide cooperative catalytic strategy for atroposelective synthesis of axially chiral aryltriazoles has been developed for the first time. Diverse structurally novel aryltriazole skeletons that cannot be accessed by traditional click reactions were synthesized in good yields with excellent enantioselectivity. Both enantiomers were easily obtained from a pair of diastereoisomeric natural quinidine- and quinine-derived squaramides. A significant Ir(I)/squaramide coordination activation, but no self-quenching phenomenon was observed in this metal/organo cooperative catalytic system.