Switchable Polymerization Triggered by Fast and Quantitative Insertion of Carbon Monoxide into Cobalt–Oxygen Bonds

A strategy that uses carbon monoxide (CO) as a molecular trigger to switch the polymerization mechanism of a cobalt Salen complex [salen=(R,R)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine] from ring-opening copolymerization (ROCOP) of epoxides/anhydrides to organometallic mediated controlled radical polymerization (OMRP) of acrylates is described. The key phenomenon is a rapid and quantitative insertion of CO into the Co−O bond, allowing for in situ transformation of the ROCOP active species (Salen)Co^III-OR into the OMRP photoinitiator (Salen)Co^III-CO₂R. The proposed mechanism, which involves CO coordination to (Salen)Co^III-OR and subsequent intramolecular rearrangement via migratory insertion has been rationalized by DFT calculations. Regulated by both CO and visible light, on-demand sequence control can be achieved for the one-pot synthesis of polyester-b-polyacrylate diblock copolymers (Đ<1.15).     

Ruthenium(II)-Catalyzed Asymmetric Inert C−H Bond Activation Assisted by a Chiral Transient Directing Group

A ruthenium(II)-catalyzed asymmetric intramolecular hydroarylation assisted by a chiral transient directing group has been developed. A series of 2,3-dihydrobenzofurans bearing chiral all-carbon quaternary stereocenters have been prepared in remarkably high yields (up to 98 %) and enantioselectivities (up to >99 % ee). By this methodology, a novel asymmetric total synthesis of CB2 receptor agonist MDA7 has been successfully developed.     

Bioorthogonal Ligation and Cleavage by Reactions of Chloroquinoxalines with ortho-Dithiophenols

A bioorthogonal ligation and cleavage method via reactions of chloroquinoxalines (CQ) and ortho-dithiophenols (DT) is presented. Double nucleophilic substitutions of ortho-dithiophenols to chloroquinoxalines provide conjugates containing tetracyclic benzo[5,6][1,4]dithiino[2,3-b]quinoxaline with strong built-in fluorescence together with release of the other functional molecules. Three cleavable linkers were designed and successfully used in release of the molecules containing biotin from the protein conjugates. The CQ-DT bioorthogonal reactions can be applied for the bioorthogonal ligations, bioorthogonal cleavages, and trans-tagging of proteins, and show advantages of readily accessible unnatural orthogonal groups, appealing reaction kinetics (k₂≈1.3 m ⁻¹ s⁻¹), excellent biocompatibility of orthogonal groups, and high stability of conjugates. This complements previous bioorthogonal reactions and is a new route for protein-fishing applications and in-gel fluorescence analysis.     

Three-dimensional Octameric Assembly of Icosahedral M13 Units in [Au8Ag57(Dppp)4(C6H11S)32Cl2]Cl and its [Au8Ag55(Dppp)4(C6H11S)34][BPh4]2 Derivative

The high-dimensional (that is, three-dimensional (3D)) assembly of nanomaterials is an effective means of improving their properties; however, achieving this assembly at the atomic level remains challenging. Herein, we obtained a novel nanocluster, [Au₈Ag₅₇(Dppp)₄(C₆H₁₁S)₃₂C_l2]Cl (Dppp=1,3-bis(diphenylphosphino)propane) showing a 3D octameric assembly mode involving the kernel penetration of eight complete icosahedral Au@Ag₁₀Au₂ units for the first time. The atomically precise structure was determined by single-crystal X-ray diffraction, and further confirmed by thermogravimetric analysis, X-ray photoelectron spectroscopy, and electrospray ionization mass spectrometry measurements. Furthermore, ligand-induced transformation prompted the conversion of [Au₈Ag₅₇(Dppp)₄(C₆H₁₁S)₃₂Cl₂]Cl, with complete octameric fusion into [Au₈Ag₅₅(Dppp)₄(C₆H₁₁S)₃₄][BPh₄]₂, with incomplete octameric fusion. These observations will hopefully facilitate further research on the assembly of M₁₃ nanobuilding blocks.     

Enantioselective Construction of Axially Chiral Amino Sulfide Vinyl Arenes by Chiral Sulfide-Catalyzed Electrophilic Carbothiolation of Alkynes

The enantioselective construction of axially chiral compounds by electrophilic carbothiolation of alkynes is disclosed for the first time. This enantioselective transformation is enabled by the use of a Ts-protected bifunctional sulfide catalyst and Ms-protected ortho-alkynylaryl amines (Ts=tosyl; Ms=mesyl). Both electrophilic arylthiolating and electrophilic trifluoromethylthiolating reagents are suitable for this reaction. The obtained products of axially chiral vinyl–aryl amino sulfides can be easily converted into biaryl amino sulfides, biaryl amino sulfoxides, biaryl amines, vinyl–aryl amines, and other valuable difunctionalized compounds.     

A Supported Bismuth Halide Perovskite Photocatalyst for Selective Aliphatic and Aromatic C–H Bond Activation

Direct selective oxidation of hydrocarbons to oxygenates by O₂ is challenging. Catalysts are limited by the low activity and narrow application scope, and the main focus is on active C−H bonds at benzylic positions. In this work, stable, lead-free, Cs₃Bi₂Br₉ halide perovskites are integrated within the pore channels of mesoporous SBA-15 silica and demonstrate their photocatalytic potentials for C−H bond activation. The composite photocatalysts can effectively oxidize hydrocarbons (C₅ to C₁₆ including aromatic and aliphatic alkanes) with a conversion rate up to 32900 μmol g_cat⁻¹ h⁻¹ and excellent selectivity (>99 %) towards aldehydes and ketones under visible-light irradiation. Isotopic labeling, in situ spectroscopic studies, and DFT calculations reveal that well-dispersed small perovskite nanoparticles (2–5 nm) possess enhanced electron–hole separation and a close contact with hydrocarbons that facilitates C(sp³)−H bond activation by photoinduced charges.     

Charge-Tagged DNA Radicals in the Gas Phase Characterized by UV/Vis Photodissociation Action Spectroscopy

Adenosine radicals tagged with a fixed-charge group were generated in the gas phase and structurally characterized by tandem mass spectrometry, deuterium labeling, and UV/Vis action spectroscopy. Experimental results in combination with Born–Oppenheimer molecular dynamics, ab initio, and excited-state calculations led to unambiguous assignment of adenosine radicals as N-7 hydrogen atom adducts. The charge-tagged radicals were found to be electronically equivalent to natural DNA nucleoside radicals.     

Pyridinylidenaminophosphines: Facile Access to Highly Electron-Rich Phosphines

Electron-rich tertiary phosphines are valuable species in chemical synthesis. However, their broad application as ligands in catalysis and reagents in stoichiometric reactions is often limited by their costly synthesis. Herein, we report the synthesis and properties of a series of phosphines with 1-alkylpyridin-4-ylidenamino and 1-alkylpyridin-2-ylidenamino substituents that are accessible in a very short and scalable route starting from commercially available aminopyridines and chlorophosphines. The determination of the Tolman electronic parameter (TEP) value reveals that the electron donor ability can be tuned by the substituent pattern at the aminopyridine backbone and it can exceed that of common alkylphosphines and N-heterocyclic carbenes. The potential of the new phosphines as strong nucleophiles in phosphine-mediated transformations is demonstrated by the formation of Lewis base adducts with CO₂ and CS₂. In addition, the coordination chemistry of the new phosphines towards Cu^I, Au^I, and Pd^II metal centers has been explored, and a convenient procedure to introduce the most basic phosphine into metal complexes starting from air-stable phosphonium salt is described.