Showing papers on "Lewis acids and bases published in 2019"

Porous Crystalline Olefin-Linked Covalent Organic Frameworks

Abstract: The first unsubstituted olefin-linked covalent organic framework, termed COF-701, was made by linking 2,4,6-trimethyl-1,3,5-triazine (TMT) and 4,4′-biphenyldicarbaldehyde (BPDA) through Aldol condensation. Formation of the unsubstituted olefin (-CH═CH-) linkage upon reticulation is confirmed by Fourier transform infrared (FT-IR) spectroscopy and solid-state ¹³C cross-polarization magic angle spinning (CP-MAS) NMR spectroscopy of the framework and of its ¹³C-isotope-labeled analogue. COF-701 is found to be porous (1715 m² g–¹) and to retain its composition and crystallinity under both strongly acidic and basic conditions. The high chemical robustness is attributed to the unsubstituted olefin linkages. Immobilization of the strong Lewis acid BF₃·OEt₂ in the pores of the structure yields BF₃⊂COF-701. In the material, the catalytic activity of the guest is retained, as evidenced in a benchmark Diels–Alder reaction.

New Directions for Frustrated Lewis Pair Chemistry

Abstract: The concerted action of a Lewis acid and base can activate H2 and other small molecules. Such frustrated Lewis pairs (FLPs) have garnered much attention and prompted many investigations into the activation of small molecules and catalysis. Although the nature, mechanism of action, and range of FLP systems continues to expand, this concept has also inspired ever-widening chemistry. Applications in hydrogenation and polymerization catalysis, as well as in synthetic chemistry, have provided selective processes and metal-free protocols. Heterogeneous FLP catalysts are emerging, and polymeric FLPs offer avenues to unique materials and strategies for sensing and carbon capture. The prospects for further impact of this remarkably simple reaction paradigm are considered.

Synergistic effects of Cu2O-decorated CeO2 on photocatalytic CO2 reduction: Surface Lewis acid/base and oxygen defect

Abstract: Ceria (CeO2) with abundant oxygen defects, surface alkalinity, low cost effectiveness and admirable redox ability could be used in the photoreduction of CO2. However, little attention has been paid to the interaction of reactant CO2 molecules on CeO2–based photocatalysts. In this work, Cu2O nanoparticles were applied to the modification of the properties of Lewis acid/base, surface oxygen defect content and visible light adsorption of CeO2, and the adsorption/activation abilities of CO2 reactant on Cu2O/CeO2 and CeO2 photocatalysts were investigated in comparison. The photocatalytic performance showed that Cu2O/CeO2 had better activity than CeO2. And the loading of Cu2O resulted in more oxygen defects and Ce3+ species, which was helpful for available visible light adsorption and higher charge-separation efficiency. Furthermore, CO2-TPD, CO2-adsorption DRIFTS and in-situ ESR results demonstrated that the synergistic effects of Cu2O/CeO2 were beneficial for more generated carboxylate and CO2− radicals, instead of carbonate species which promoted CO2 reduction to CO.

Asymmetric Photocatalysis with Bis-cyclometalated Rhodium Complexes

Abstract: Aspects of sustainability are playing an increasingly important role for the development of new synthetic methods. In this context, the combination of asymmetric catalysis, which is considered one of the most economic strategies to generate nonracemic chiral compounds, and visible light as an abundant source of energy to induce or activate chemical reactions has recently gained much attention. Furthermore, the combination of photochemistry with asymmetric catalysis provides new opportunity for the development of mechanistically unique reaction schemes. However, the development of such asymmetric photocatalysis is very challenging and two main problems can be pinpointed to undesirable photochemical background reactions and to difficulties in controlling the stereochemistry with photochemically generated highly reactive intermediates. In this Account, we present and discuss asymmetric photocatalysis using one of the currently most versatile photoactivatable asymmetric catalysts, namely, reactive bis-cyclometalated rhodium(III) complexes. The catalysts contain two inert cyclometalating 5-( tert-butyl)-2-phenyl benzoxazole or benzothiazole ligands together with two labile acetonitriles, and the overall chirality is due to a stereogenic metal center. The bis-cyclometalated rhodium complexes serve as excellent chiral Lewis acids for substrates such as 2-acyl imidazoles and N-acyl pyrazoles, which, upon replacement of the two labile acetonitrile ligands, coordinate to the rhodium center in a 2-point fashion. These rhodium-substrate intermediates display unique photophysical and photochemical properties and are often the photoactive intermediates in the developed asymmetric photocatalysis reaction schemes. This combination of visible light excitation to generate long-lived photoexcited states and intrinsic Lewis acid reactivity opens the door for a multitude of visible-light-induced asymmetric conversions. In a first mode of reactivity, bis-cyclometalated rhodium complexes function as chiral Lewis acids to control asymmetric radical reactions of rhodium enolates with electron-deficient radicals, rhodium-coordinated enones with electron-rich radicals, or rhodium-bound radicals generated by photoinduced single electron transfer. The rhodium-substrate complexes in their ground states are key intermediates of the asymmetric catalysis, while separate photoredox cycles initiate radical generations via single electron transfer with either the rhodium-substrate complexes or additional photoactive compounds serving as the photoredox catalyst (secondary asymmetric photocatalysis). In a second mode of reactivity, the rhodium-substrate complexes serve as photoexcited intermediates within the asymmetric catalysis cycle (primary asymmetric photocatalysis) and undergo stereocontrolled chemistry either upon single electron transfer or by direct bond forming reactions out of the excited state. These multiple modes of intertwining photochemistry with asymmetric catalysis have been applied to asymmetric α- and β-alkylations, α- and β-aminations, β-C-H functionalization of carbonyl compounds, [3 + 2] photocycloadditions between cyclopropanes and alkenes or alkynes, [2 + 2] photocycloadditions of enones with alkenes, dearomative [2 + 2] photocycloadditions, and [2 + 3] photocycloadditions of enones with vinyl azides. We anticipate that these reaction schemes of chiral bis-cyclometalated rhodium complexes as (photoactive) chiral Lewis acids will spur the development of new photocatalysts for visible-light-induced asymmetric catalysis.

Heteropolyacid supported on Zr-Beta zeolite as an active catalyst for one-pot transformation of furfural to γ-valerolactone

Abstract: A novel bifunctional catalyst that enables an efficient one-pot conversion of furfural into γ-valerolactone (GVL) has been developed by anchoring heteropolyacid (HPA) on Zr-Beta zeolite The catalysts were prepared by a post-synthesis procedure, which consists of the dealumination of Al-Beta, incorporation of Zr into the beta framework through solid-state ion-exchange and impregnation of the HPA Zr-Beta is used as a Lewis acid catalyst to catalyze the transfer hydrogenation of furfural and levulinic acid/ester using 2-propanol as a hydrogen donor To deal with the inability of Zr-Beta to catalyze the hydrolytic ring-opening of furans toward GVL, phosphotungstic acid (HPW) and silicotungstic acid (HSiW) were introduced to the Zr-Beta as BrOnsted acid sites The characterization of the catalysts using XRD, UV–vis and XPS as well as TPD of ammonia and FT-IR spectroscopy of the adsorbed pyridine revealed that the HPA/Zr-Beta possesses both isolated Lewis and BrOnsted acid sites When they were applied to the one-pot cascade conversion of furfural, the initial activity of the HPA/Zr-Beta toward GVL production were 2–3 times greater than that for Zr-Beta due to the enhanced hydrolytic ring-opening of the furans promoted by the added BrOnsted acidity Especially, HPW loaded Zr-Beta demonstrated a remarkable GVL yield of ∼70% at 433 K after 24 h due to its high thermal stability and stronger BrOnsted acidity, and its activity far surpasses that of the conventional Sn-Al-Beta zeolite (∼40%) Overall, this study demonstrates that an incorporation of HPA into Lewis acid Sn- or Zr-Beta zeolites is an effective strategy to create isolated Lewis and BrOnsted acid sites within a single catalyst, thereby allowing the selective cascade catalysis for the cost-effective production of high-value chemicals

Chalcogen Bonding Catalysis of a Nitro-Michael Reaction.

Abstract: Chalcogen bonding is the non-covalent interaction between Lewis acidic chalcogen substituents and Lewis bases. Herein, we present the first application of dicationic tellurium-based chalcogen bond donors in the nitro-Michael reaction between trans-β-nitrostyrene and indoles. This also constitutes the first activation of nitro derivatives by chalcogen bonding (and halogen bonding). The catalysts showed rate accelerations of more than a factor of 300 compared to strongly Lewis acidic hydrogen bond donors. Several comparison experiments, titrations, and DFT calculations support a chalcogen-bonding-based mode of activation of β-nitrostyrene.

Towards understanding the doping mechanism of organic semiconductors by Lewis acids

Abstract: Precise doping of organic semiconductors allows control over the conductivity of these materials, an essential parameter in electronic applications. Although Lewis acids have recently shown promise as dopants for solution-processed polymers, their doping mechanism is not yet fully understood. In this study, we found that B(C6F5)3 is a superior dopant to the other Lewis acids investigated (BF3, BBr3 and AlCl3). Experiments indicate that Lewis acid-base adduct formation with polymers inhibits the doping process. Electron-nuclear double-resonance and nuclear magnetic resonance experiments, together with density functional theory, show that p-type doping occurs by generation of a water-Lewis acid complex with substantial Bronsted acidity, followed by protonation of the polymer backbone and electron transfer from a neutral chain segment to a positively charged, protonated one. This study provides insight into a potential path for protonic acid doping and shows how trace levels of water can transform Lewis acids into powerful Bronsted acids.

Transition-metal free C–C bond cleavage/borylation of cycloketone oxime esters

Abstract: An efficient transition-metal free C-C bond cleavage/borylation of cycloketone oxime esters has been described. In this reaction, the B2(OH)4 reagent not only served as the boron source but also acted as an electron donor source through formation of a complex with a DMAc-like Lewis base. This complex could be used as an efficient single electron reductant in other ring-opening transformations of cycloketone oxime esters. Free-radical trapping, radical-clock, and DFT calculations all suggest a radical pathway for this transformation.

Enantioselective [2+2] Cycloadditions of Cinnamate Esters: Generalizing Lewis Acid Catalysis of Triplet Energy Transfer.

Abstract: We report the enantioselective [2+2] cycloaddition of simple cinnamate esters, the products of which are useful synthons for the controlled assembly of cyclobutane natural products. This method utilizes a cocatalytic system in which a chiral Lewis acid accelerates the transfer of triplet energy from an excited-state Ir(III) photocatalyst to the cinnamate ester. Computational evidence indicates that the principal role of the Lewis acid cocatalyst is to lower the absolute energies of the substrate frontier molecular orbitals, leading to greater electronic coupling between the sensitizer and substrate and increasing the rate of the energy transfer event. These results suggest Lewis acids can have multiple beneficial effects on triplet sensitization reactions, impacting both the thermodynamic driving force and kinetics of Dexter energy transfer.

Metal-free electrocatalyst for reducing nitrogen to ammonia using a Lewis acid pair

Abstract: Electrocatalytic nitrogen reduction reaction (NRR) is a promising way for the sustainable production of ammonia. However, it suffers from slow kinetics due to the difficulty of NN bond activation and the side hydrogen evolution reaction. Herein, on the basis of the concept of “Lewis acid pair”, we propose a metal-free electrocatalyst based on boron-decorated black phosphorus by using extensive first-principles calculations. In the integrated structure of the catalyst, the doped B atoms serve as Lewis acid pairs and catalytic centers, while the channels of BP provide structural advantages for hosting the pair and activating the NN bond. A new strategy of nitrogen activation based on the pull–pull effect is thus developed. Performance evaluations show that this metal-free catalyst is highly efficient for electrocatalytic nitrogen reduction with an ultra-low onset-potential of 0.19 V. This work opens a new possible avenue for nitrogen activation and can be generally applied to other two-dimensional or bulk materials.

meta-Selective C–H Borylation of Benzamides and Pyridines by an Iridium–Lewis Acid Bifunctional Catalyst

Abstract: We report herein the iridium-catalyzed meta-selective C-H borylation of benzamides by using a newly designed 2,2'-bipyridine (bpy) ligand bearing an alkylaluminum biphenoxide moiety. We also demonstrate the iridium-catalyzed C3-selective C-H borylation of pyridine with a 1,10-phenanthroline (Phen) ligand bearing an alkylborane moiety. It is proposed that the Lewis acid-base interaction between the Lewis acid moiety and the aminocarbonyl group or the sp2-hybridized nitrogen atom accelerates the reaction and controls the site-selectivity.

Schottky Barrier Induced Coupled Interface of Electron-Rich N-Doped Carbon and Electron-Deficient Cu: In-Built Lewis Acid-Base Pairs for Highly Efficient CO2 Fixation.

Abstract: Highly efficient fixation of CO2 for the synthesis of useful organic carbonates has drawn much attention. The design of sustainable Lewis acid-base pairs, which has mainly relied on expensive organic ligands, is the key challenge in the activation of the substrate and CO2 molecule. Here, we report the application of Mott-Schottky type nanohybrids composed of electron-deficient Cu and electron-rich N-doped carbon for CO2 fixation. A ligand-free and additive-free method was used to boost the basicity of the carbon supports and the acidity of Cu by increasing the Schottky barrier at their boundary, mimicking the beneficial function of organic ligands acting as the Lewis acid and base in metal-organic frameworks (MOFs) or polymers and simultaneously avoiding the possible deactivation associated with the necessary stability of a heterogeneous catalyst. The optimal Cu/NC-0.5 catalyst exhibited a remarkably high turnover frequency (TOF) value of 615 h-1 at 80 °C, which is 10 times higher than that of the state-of-the-art metal-based heterogeneous catalysts in the literature.

Low-temperature hydrogenation of dimethyl oxalate to ethylene glycol via ternary synergistic catalysis of Cu and acid−base sites

Abstract: Metal-support synergistic catalysis plays a crucial role in heterogeneous reaction processes from viewpoint of both fundamental research and practical applications. Herein, a series of Cu-based nanocatalysts were prepared by virtue of topotactic structure transformation from CuMgAl-layered double hydroxide (CuMgAl − LDH) precursors. Various in situ investigations including XRD, XPS, EXAFS and FTIR demonstrate that the structural transformation of CuMgAl − LDH results in well-dispersed Cu nanoparticles (metallic Cu° as the single species) supported on mixed metal oxides (MgO and Al2O3, denoted as Cu/MMO). The optimal catalyst (Cu/MMO−S3) exhibits an excellent catalytic performance toward hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) (yield: 94.4%) at an exceptionally low operation temperature (438 K). This is, to the best of our knowledge, at least 30―40 K lower than normally accepted temperature for Cu-based catalysts (above 473 K). Structure − property correlation investigations were performed via in situ FTIR, N2O pulse chemisorption, NH3−TPD and CO2−TPD, and the results revealed that a ternary synergistic catalysis of Cu and acid − base sites makes a predominant contribution: Lewis acid sites (Al3+) and medium-strong basic sites (Mg2+−O2− pair) of supports serve as active sites for adsorption of polarized C O/C O group in DMO molecule; while H2 undergoes dissociation adsorption on Cu° site. This precise control over metal and acid − base sites based on LDHs precursor approach would lead to new possibilities in rational design and preparation of heterogeneous catalysts for hydrogenation of C O/C O group.

The Role of Alkali Metal in α‑MnO 2 Catalyzed Ammonia‑Selective Catalysis

Abstract: The unexpected phenomenon and mechanism of the alkali metal involved NH3 selective catalysis are reported. Incorporation of K+ (4.22 wt %) in the tunnels of α-MnO2 greatly improved its activity at low temperature (50-200 °C, 100 % conversion of NOx vs. 50.6 % conversion over pristine α-MnO2 at 150 °C). Experiment and theory demonstrated the atomic role of incorporated K+ in α-MnO2 . Results showed that K+ in the tunnels could form a stable coordination with eight nearby O sp3 atoms. The columbic interaction between the trapped K+ and O atoms can rearrange the charge population of nearby Mn and O atoms, thus making the topmost five-coordinated unsaturated Mn cations (Mn5c , the Lewis acid sites) more positive. Therefore, the more positively charged Mn5c can better chemically adsorb and activate the NH3 molecules compared with its pristine counterpart, which is crucial for subsequent reactions.

Lewis Acid–Base Synergistic Catalysis for Polyethylene Terephthalate Degradation by 1,3-Dimethylurea/Zn(OAc)2 Deep Eutectic Solvent

Abstract: Deep eutectic solvents (DESs) become more attractive in the catalytic field due to their biodegradation, low toxicity, and designability. This study focused on the active sites and influencing fact...

The alkali resistance of CuNbTi catalyst for selective reduction of NO by NH3: A comparative investigation with VWTi catalyst

Abstract: The alkali metal poisoned CuNbTi and VWTi catalysts were prepared by wetness impregnation method. Poisoning effects of various K2O mass ratios (0.1%–2%) on CuNbTi and VWTi catalysts were studied, respectively. CuNbTi exhibited an excellent alkali metal resistance that 2%K2O-CuNbTi still remained 80% NOx conversion efficiency and 98% N2 selectivity while 2%K2O-VWTi was completely deactivated. Moreover, different alkali metals (K, Na, Ca, Mg) with the same molar ratio were doped on CuNbTi. The poisoned degree followed the order: K2O > Na2O > CaO > MgO. Then 2%K2O-CuNbTi and 2%K2O-VWTi were selected for follow-up study. To understand the poisoning mechanism, further investigations were performed by SEM, XRD, N2-physisorption, XPS, EPR, NH3-TPD, Py-IR, H2-TPR, in situ DRIFTS characterizations and DFT calculations. The particle of CuNbTi and VWTi agglomerated and the surface area decreased after 2%K2O loading. Loss of acid sites and drop of reducibility resulted in the deactivation of 2%K2O-VWTi. By contrast, experimental and computational results indicated that the alkali resistance of 2%K2O-CuNbTi was mainly due to the interaction between Ti2NbOx support and K atoms that K atoms were preferentially bound to Nb OH and Nb O with a lower bonding energy of −2.33 eV–−2.83 eV when Cu atoms were coordinated to Ti O with a binding energy of −1.54 eV. This protected the active copper species from linking to K2O and the weak acid sites were preserved with the increasing isolated Cu2+. Ti2NbOx weakened the impact of potassium on NH3 adsorbing over the catalyst while the preserved copper species provided adsorption sites and redox ability for NH3-SCR reaction. Hence, the synergetic effect of copper and niobium species contributed to the alkali metal resistance. Ti2NbOx trapped the potassium and retained active copper species over 2%K2O-CuNbTi catalyst while potassium deactivated both TiO2 and active vanadium species on 2%K2O-VWTi catalyst. Meanwhile, both Eley-Rideal (E-R) and Langmuir-Hinshelwood (H-L) mechanisms with adsorbed NH3 coordinated to the Lewis acid sites and bidentate nitrate as the dominating intermediate species existed during the NH3-SCR reaction procedure over 2%K2O-CuNbTi at 225 °C.

Divalent hard Lewis acid doped CsPbBr3 films for 9.63%-efficiency and ultra-stable all-inorganic perovskite solar cells

Abstract: Substitution of Pb2+ sites with smaller isovalent ions has been regarded as an effective strategy to optimize the crystal lattice of organic–inorganic hybrid perovskites such as releasing lattice strain, increasing the formation energy of vacancies and tuning the bandgap energy distribution. We report here the compositional engineering of the inorganic CsPbBr3 perovskite by doping divalent hard Lewis acids (Mg2+, Ca2+, Sr2+ and Ba2+) and their application in all-inorganic perovskite solar cells free of hole transporting layers and precious metal electrodes. By optimizing the doping dosage, a maximal power conversion efficiency as high as 9.63% is achieved for a CsPb0.97Sr0.03Br3 based photovoltaic device, mainly attributed to the enlarged grain sizes and suppressed formation of point defect (vacancies) within perovskite films, therefore reducing the photocurrent loss within modules. Furthermore, the unencapsulated Sr-containing solar cell shows ultrastability comparable to that of state-of-the-art CsPbBr3 perovskite solar cells under persistent attack in 80% relative humidity over 800 h. The increased efficiency and improved stability demonstrate all-inorganic perovskite solar cells with divalent hard Lewis acid doped CsPbBr3 perovskites to be a new frontier for thin-film photovoltaics.

Donor-Acceptor Cyclopropanes in the Synthesis of Carbocycles.

Abstract: Donor-acceptor cyclopropanes not only participate in a broad range of ring openings with nucleophiles, electrophiles, radical and red-ox agents, but also are excellent substrates for various (3+n)-cycloaddition and (3+n)-annulation processes. Moreover, under treatment with Lewis acid donor-acceptor cyclopropanes can produce new ring systems via isomerization or cyclodimerization. Authors' contribution to the synthesis of diverse carbocycles from donor-acceptor cyclopropanes is summarized in this account.

α-Functionalization of Cyclic Secondary Amines: Lewis Acid Promoted Addition of Organometallics to Transient Imines.

Abstract: Cyclic imines, generated in situ from their corresponding N-lithiated amines and a ketone hydride acceptor, undergo reactions with a range of organometallic nucleophiles to generate α-functionalized amines in a single operation. Activation of the transient imines by Lewis acids that are compatible with the presence of lithium alkoxides was found to be crucial to accommodate a broad range of nucleophiles including lithium acetylides, Grignard reagents, and aryllithiums with attenuated reactivities.

In Situ Formation of Frustrated Lewis Pairs in a Water‐Tolerant Metal‐Organic Framework for the Transformation of CO2

Abstract: Frustrated Lewis pairs (FLPs) consist of sterically hindered Lewis acids and Lewis bases, which provide high catalytic activity towards non-metal-mediated activation of "inert" small molecules, including CO2 among others. One critical issue of homogeneous FLPs, however, is their instability upon recycling, leading to catalytic deactivation. Herein, we provide a solution to this issue by incorporating a bulky Lewis acid-functionalized ligand into a water-tolerant metal-organic framework (MOF), named SION-105, and employing Lewis basic diamine substrates for the in situ formation of FLPs within the MOF. Using CO2 as a C1-feedstock, this combination allows for the efficient transformation of a variety of diamine substrates into benzimidazoles. SION-105 can be easily recycled by washing with MeOH and reused multiple times without losing its identity and catalytic activity, highlighting the advantage of the MOF approach in FLP chemistry.

Recent advances in photocatalytic C–S/P–S bond formation via the generation of sulfur centered radicals and functionalization

Abstract: Thioyl and sulfonyl radicals are usually produced from various thiols and sulfonyl derivatives in high efficiency by single-electron-transfer (SET) oxidation. The generated sulfur (thioyl/sulfonyl) radicals are also highly reactive intermediates having various applications in the construction of organosulfur compounds in the field of organic synthesis. Recently, photoredox-catalyzed C–S/P–S bond formation via the generation of sulfur centered radicals has been studied extensively. In the photoredox catalytic process, a variety of S–H, S–S, S–C, S–N, and S–X (F, Cl, Br, I) bonds, and even active sulfone-containing skeletons can be easily transformed into the corresponding thioyl/sulfonyl radicals. Some of these transformations are achieved by a combination of photoredox catalysts (i.e., TiO2, Bi2O3, eosin Y, fac-[Ir(ppy)3], [Ru(bpy)3]2+) and other catalysts such as strong bases, Lewis acids, organocatalysts and transition metal catalysts. Compared with previous methods, photoredox catalysis is inexpensive and features the advantages of high efficiency and easy utilization in addition to being environmentally-benign. In this review, we have focused on the research on photoredox-catalyzed C–S/P–S bond formation via the generation of thioyl/sulfonyl radicals and further functionalization in the past few years. We hope to offer chemists the tools to open the door for further progress in organsulfur chemistry.

Efficient Photocatalytic CO2 Reduction by a Ni(II) Complex Having Pyridine Pendants through Capturing a Mg2+ Ion as a Lewis-Acid Cocatalyst.

Abstract: We have synthesized a new Ni(II) complex having an S2N2-tetradentate ligand with two noncoordinating pyridine pendants as binding sites of Lewis-acidic metal ions in the vicinity of the Ni center, ...

Triarylborane-Catalyzed Formation of Cyclic Organic Carbonates and Polycarbonates

Abstract: Effective utilization of carbon dioxide as a C1 feedstock is an ongoing challenge for chemists. The catalytic reaction of epoxides and carbon dioxide to produce cyclic or polycarbonates has become ...

Lewis Acid Dominant Windmill-Shaped V8 Clusters: A Bifunctional Heterogeneous Catalyst for CO2 Cycloaddition and Oxidation of Sulfides.

Abstract: Carbon dioxide (CO2) and sulfides in gasoline are the main causes of air pollution. Considerable attention has been devoted to solving the problems, and the catalytic reaction seems to be a good ch...

Photocatalytic enantioselective α-aminoalkylation of acyclic imine derivatives by a chiral copper catalyst.

Abstract: Copper-based asymmetric photocatalysis has great potential in the development of green synthetic approaches to chiral molecules. However, there are several formidable challenges associated with such a conception. These include the relatively weak visible light absorption, short excited-state lifetimes, incompatibility of different catalytic cycles, and the difficulty of the stereocontrol. We report here an effective strategy by means of single-electron-transfer (SET) initiated formation of radicals and photoactive intermediates to address the long-standing problems. Through elaborate selection of well-matched reaction partners, the chiral bisoxazoline copper catalyst is engaged in the SET process, photoredox catalysis, Lewis acid activation and asymmetric induction. Accordingly, a highly enantioselective photocatalytic α-aminoalkylation of acyclic imine derivatives has been accessed. This strategy sheds light on how to make use of diverse functions of a single transition metal catalyst in one reaction, and offers an economic and simplified approach to construction of highly valuable chiral vicinal diamines. Copper-based asymmetric photocatalysis has great synthetic potential, however it has been rarely exploited due to challenges inherent to such systems. Here, a chiral bisoxazoline copper catalyst is involved in a SET process, photoredox catalysis, Lewis acid activation and asymmetric induction to construct chiral vicinal diamines.