Visible-Light-Promoted Asymmetric Catalysis by Chiral Complexes of First-Row Transition Metals

Asymmetric Cross-Coupling of Aldehydes with Diverse Carbonyl or Iminyl Compounds by Photoredox-Mediated Cobalt Catalysis

The asymmetric cross-coupling of unsaturated bonds, hampered by their comparable polarity and reactivity, as well as the scarcity of efficient catalytic systems capable of diastereo- and enantiocontrol, presents a significant hurdle in organic synthesis. In this study, we introduce a highly adaptable photochemical cobalt catalysis framework that facilitates chemo- and stereoselective reductive cross-couplings between common aldehydes with a broad array of carbonyl and iminyl compounds, including N-acylhydrazones, aryl ketones, aldehydes, and α-keto esters. Our methodology hinges on a synergistic mechanism driven by photoredox-induced single-electron reduction and subsequent radical-radical coupling, all precisely guided by a chiral cobalt catalyst. Various optically enriched β-amino alcohols and unsymmetrical 1,2-diol derivatives (80 examples) have been synthesized with good yields (up to 90% yield) and high stereoselectivities (up to >20:1 dr, 99% ee). Of particular note, this approach accomplishes unattainable photochemical asymmetric transformations of aldehydes with disparate carbonyl partners without reliance on any external photosensitizer, thereby further emphasizing its versatility and cost-efficiency.

Magnetic CoFe1.95Y0.05O4-Decorated Ag3PO4 as Superior and Recyclable Photocatalyst for Dye Degradation

The Ag₃PO₄/CoFe_1.95Y_0.05O₄ nanocomposite with magnetic properties was simply synthesized by the hydrothermal method. The structure and morphology of the prepared material were characterized, and its photocatalytic activity for degradation of the methylene blue and rhodamine B dyes was also tested. It was revealed that the Ag₃PO₄ in the nanocomposite exhibited a smaller size and higher efficiency in degrading dyes than the individually synthesized Ag₃PO₄ when exposed to light. Furthermore, the magnetic properties of CoFe_1.95Y_0.05O₄ enabled the nanocomposite to possess magnetic separation capabilities. The stable crystal structure and effective degradation ability of the nanocomposite were demonstrated through cyclic degradation experiments. It was shown that Ag₃PO₄/CoFe_1.95Y_0.05O₄-0.2 could deliver the highest activity and stability in degrading the dyes, and 98% of the dyes could be reduced within 30 min. Additionally, the photocatalytic enhancement mechanism and cyclic degradation stability of the magnetic nanocomposites were also proposed.

Asymmetric imino-acylation of alkenes enabled by HAT-photo/nickel cocatalysis

By merging nickel-mediated facially selective aza-Heck cyclization and radical acyl C-H activation promoted by tetrabutylammonium decatungstate (TBADT) as a hydrogen atom transfer (HAT) photocatalyst, we accomplish an asymmetric imino-acylation of oxime ester-tethered alkenes with readily available aldehydes as the acyl source, enabling the synthesis of highly enantioenriched pyrrolines bearing an acyl-substituted stereogenic center under mild conditions. Preliminary mechanistic studies support a Ni(i)/Ni(ii)/Ni(iii) catalytic sequence involving the intramolecular migratory insertion of a tethered olefinic unit into the Ni(iii)-N bond as the enantiodiscriminating step.

Visible Light Induced C-H/N-H and C-X Bonds Reactions

Herein, we report efficient visible light-induced photoredox reactions of C–H/N–H and C–X Bonds. These methods have provided access to varied portfolio of synthetically important γ-ketoesters, azaspirocyclic cyclohexadienones spirocyclohexadienones, multisubstituted benzimidazole derivatives, substituted N,2-diarylacetamide, 2-arylpyridines and 2-arylquinolines in good yields and under mild conditions. Moreover, we have successfully discussed the construction through visible light-induction by an intermolecular radical addition, dearomative cyclization, aryl migration and desulfonylation. Similarly, we also spotlight the visible light-catalyzed aerobic C–N bond activation from well-known building blocks through cyclization, elimination and aromatization. The potential use of a wide portfolio of simple ketones and available primary amines has made this transformation very attractive.

Terpyridine Diphosphine Ruthenium Complexes as Efficient Photocatalysts for the Transfer Hydrogenation of Carbonyl Compounds

The cationic achiral and chiral terpyridine diphosphine ruthenium complexes [RuCl(PP)(tpy)]Cl (PP=dppp (1), (R,R)-Skewphos (2) and (S,S)-Skewphos (3)) are easily obtained in 85-88 % yield through a one-pot synthesis from [RuCl₂ (PPh₃ )₃ ], the diphosphine and 2,2':6',2''-terpyridine (tpy) in 1-butanol. Treatment of 1-3 with NaPF₆ in methanol at RT affords quantitatively the corresponding derivatives [RuCl(PP)(tpy)]PF₆ (PP=dppp (1 a), (R,R)-Skewphos (2 a) and (S,S)-Skewphos (3 a)). Reaction of [RuCl₂ (PPh₃ )₃ ] with (S,R)-Josiphos or (R)-BINAP in toluene, followed by treatment with tpy in 1-butanol and finally with NaPF₆ in MeOH gives [RuCl(PP)(tpy)]PF₆ (PP=(S,R)-Josiphos (4 a), (R)-BINAP (5 a)) isolated in 78 % and 86 % yield, respectively. The chiral derivatives have been isolated as single stereoisomers and 3 a, 4 a have been characterized by single crystal X-ray diffraction studies. The tpy complexes with NaOiPr display high photocatalytic activity in the transfer hydrogenation (TH) of carbonyl compounds using 2-propanol as the only hydrogen donor and visible light at 30 °C, at remarkably high S/C (up to 5000) and TOF values up to 264 h^-1 . The chiral enantiomers 2, 2 a and 3, 3 a induce the asymmetric photocatalytic TH of acetophenone, affording (S)- and (R)-1-phenylethanol with 51 and 52 % ee, respectively, in a MeOH/2-propanol mixture.

Chiral polycyclic benzosultams from photocatalytic diastereo- and enantioselective benzylic C–H functionalization

Photocatalytic diastereo- and enantioselective C(sp3)–H functionalization/intramolecular cyclization reactions have been achieved, delivering optically active polycyclic benzosultams and fused tetrahydroisoquinolines.