Synthesis and Spectroscopic Properties of a Covalently Linked Porphyrin–Fullerene C60 Dyad

A covalently linked porphyrin–fullerene C₆₀ dyad 6 was conveniently synthesized by 1,3‐dipolar cycloaddition using 5‐(4‐carbonylphenyl)‐10,15,20‐tris(4‐methoxylphenyl)porphyrin 5, N‐methylglycine and fullerene C₆₀. Spectroscopic studies show that dyad 6 is a promising architecture with potential application as photoactive organic material.     

Photoswitchable Sol–Gel Transitions and Catalysis Mediated by Polymer Networks with Coumarin-Decorated Cu24L24 Metal–Organic Cages as Junctions

Photoresponsive materials that change in response to light have been studied for a range of applications. These materials are often metastable during irradiation, returning to their pre-irradiated state after removal of the light source. Herein, we report a polymer gel comprising poly(ethylene glycol) star polymers linked by Cu₂₄L₂₄ metal–organic cages/polyhedra (MOCs) with coumarin ligands. In the presence of UV light, a photosensitizer, and a hydrogen donor, this “polyMOC” material can be reversibly switched between Cu^II, Cu^I, and Cu⁰. The instability of the MOC junctions in the Cu^I and Cu⁰ states leads to network disassembly, forming Cu^I/Cu⁰ solutions, respectively, that are stable until re-oxidation to Cu^II and supramolecular gelation. This reversible disassembly of the polyMOC network can occur in the presence of a fixed covalent second network generated in situ by copper-catalyzed azide-alkyne cycloaddition (CuAAC), providing interpenetrating supramolecular and covalent networks.     

C−F Bond Activation Mediated by Phosphorus Compounds

The activation and functionalization of C−F bonds has garnered significant attention in the scientific community as a strategy to mitigate toxicity and environmental concerns, as well as provide new pathways to agro- and pharmaceutical chemicals and materials. Although several transition-metal-based systems have been developed for this transformation, the use of main-group compounds remains less explored. In recent years, several strategies for C−F bond activation have focused on the use of phosphorus-based reagents. In this Minireview, an overview of strategies is provided that exploits P^V and P^III-based Lewis acids as well as P^III Lewis bases in frustrated Lewis pair (FLP) protocols for hydrodefluorination, C−C couplings and C−F derivatizations.     

C–C Bond Rupture in the Oxidation of Lower (C2–C6) Alcohols with Hydrogen Peroxide Mediated by Iron-Containing Compounds

C–C bond rupture upon the oxidation of alcohols in the Fe(ClO₄)₃+ H₂O₂system in aqueous acetonitrile at room temperature is found. The relative yield of the products of C–C bond rupture is 20–30% under standard conditions for C₂and C₃alcohols and decreases in the series C₂> C₃> C₄> C₆. The alkyl radical and carboxylic acid are the products of C–C bond rupture in alcohol oxidation. Cyclohexane is a competitive inhibiting agent for C–H bond oxidation in 1-propanol, and it does not affect the yield of the products of C–C bond rupture. When H₂O₂is replaced by tert-BuOOH, the fraction of the products of C–C bond rupture decreases by an order of magnitude. Our data suggest that a non-radical intermediate, likely Fe(III) hydroperoxo complex, is responsible for C–C bond rupture in alcohol under the reaction conditions.     

Preparation of C60–Silica Hybrid Monolith by Sol-Gel Process

A C₆₀–silica hybrid monolith was prepared by the hydrosilylation of C₆₀ in the presence of platinum catalyst followed by sol-gel process with tetraethoxysilane. The hydrosilylation with trichlorosilane, triethoxysilane, chlorodiphenylsilane, and dichlorophenylsilane gave silylated C₆₀s as a brown pasty liquid. The formula was estimated to be C₆₀{Si(OEt)₃}_2.6H_2.6 or C₆₀(SiPh₂Cl)_3.2H_3.2 based on the proton nuclear magnetic resonance spectrum. A C₆₀–silica hybrid gel monolith was obtained by sol-gel process of the silylates and tetraethoxysilane in ethanol followed by aging for 3 weeks at room temperature. The monolith was brown and transparent with a diameter of 25 mm. On the other hand, the sol-gel reaction of tetraethoxysilane, trimethoxyphenylsilane, and C₆₀ provided a heterogeneous gel with a phase separation of C₆₀.     

Structural Basis for Copper–Oxygen Mediated C−H Bond Activation by the Formylglycine-Generating Enzyme

The formylglycine-generating enzyme (FGE) is a unique copper protein that catalyzes oxygen-dependent C−H activation. We describe 1.66 Å- and 1.28 Å-resolution crystal structures of FGE from Thermomonospora curvata in complex with either Ag^I or Cd^II providing definitive evidence for a high-affinity metal-binding site in this enzyme. The structures reveal a bis-cysteine linear coordination of the monovalent metal, and tetrahedral coordination of the bivalent metal. Similar coordination changes may occur in the active enzyme as a result of Cu^I/II redox cycling. Complexation of copper atoms by two cysteine residues is common among copper-trafficking proteins, but is unprecedented for redox-active copper enzymes or synthetic copper catalysts.     

Photoswitchable Phosphonate–Fullerene Hybrids with Cholinesterase Activity

Modern progress in photopharmocology calls for new generation of compounds joining bioactivity, photoswitchable properties and high selectivity of response to light wavelength. Introduced here, phosphonate–fullerene hybrids are the first representatives of such compounds. Phosphonate–fullerene hybrids were synthesized on a base of fullerene C₆₀ and organophosphates with the function of photoswitchable cholinesterase activity—phosphorylated thiazolotriazole and aminomalonate compounds and studied with FTIR, UV–VIS spectroscopy and IPC-micro neurotoxin amperometric analysis. As a result of spectroscopic and bioactivity characterization, it was not only demonstrated butyrylcholinesterase (BuChE) inhibition increase in phosphonate–fullerene hybrids compared with pure phosphonates but also pronounced response of inhibition degree to laser irradiation of hybrids. It was found opposite behavior of hybrids as a result of laser irradiation—BuChE inhibition drop-off for thiazolotriazole–fullerene and pronounced growth for aminomalonate–fullerene. The other remarkable peculiarity of presented phosphonate–fullerene hybrids is high selectivity of inhibition change degree to laser wavelength (266 or 325 nm).     

Site-Specific C(sp3)–H Aminations of Imidates and Amidines Enabled by Covalently Tethered Distonic Radical Anions

The utilization of N-centered radicals to synthesize nitrogen-containing compounds has attracted considerable attention recently, due to their powerful reactivities and the concomitant construction of C−N bonds. However, the generation and control of N-centered radicals remain particularly challenging. We report a tethering strategy using SOMO-HOMO-converted distonic radical anions for the site-specific aminations of imidates and amidines with aid of the non-covalent interaction. This reaction features a remarkably broad substrate scope and also enables the late-stage functionalization of bioactive molecules. Furthermore, the reaction mechanism is thoroughly investigated through kinetic studies, Raman spectroscopy, electron paramagnetic resonance spectroscopy, and density functional theory calculations, revealing that the aminations likely involve direct homolytic cleavage of N−H bonds and subsequently controllable 1,5 or 1,6 hydrogen atom transfer.     

C−S Cross-Coupling of Aryldiazonium Salts with Thiols Mediated by Gold

In this work, the coupling of aryldiazonium salts with thiols mediated by the readily accessible gold complex Me₂SAuCl is described. In the reported protocol, the addition of 2,2′-bipyridine as a ligand leads to higher yields than phosphines. The reaction proceeds at room temperature under soft mildconditions and has a broad scope in both the aryldiazonium salt and the thiol. Notably, the coupling works with aryldiazonium salts containing two additional substituents.     

Reactions of Initiation and Reinitiation in Polymerization Mediated by Organoborane–Oxygen Systems

The kinetics and mechanism of initiation and reinitiation reactions in the polymerization of methyl methacrylate mediated by the ammonia–tripropylborane–oxygen and 2-isopropyl-2-boraadamantane–oxygen systems are studied by ESR spectroscopy using C-phenyl-N-tert-butylnitrone and 2-methyl-2-nitrosopropane as spin traps. It is shown that alkyl and alkoxyl radicals are the main initiating radicals and the rate of initiation is directly proportional to the concentration of oxygen. Two mechanisms of radical formation are valid in the postpolymerization of methyl methacrylate at room temperature under vacuum. The first one (which is predominant) is the decomposition of poly(methyl methacrylate)–boroxyl macromolecules, i.e., the reinitiation of polymerization; the second one (additional during the first 30 min of the process) is the decomposition of borane peroxide compounds accumulated during the stage of oxidation.     

ABC–ABC-Type Directly meso–meso Linked Porphyrin Dimers

Covalently linked porphyrin oligomers are attractive because of their extended π-conjugated systems. Among various porphyrin oligomers, directly meso–meso linked porphyrin oligomers exhibit unique photophysical properties due to their strong exciton couplings derived from the alternative orthogonal geometry of the porphyrins. Although their structural and electronic properties can be greatly altered by substituents at meso positions, it is still difficult to introduce different substituents at the meso positions. Thus, it is a challenge to develop general synthetic methodologies for functional porphyrin dimers and oligomers with different substituents at the meso positions. Herein, a general synthetic strategy for ABC–ABC-type directly meso–meso linked porphyrin dimers by stepwise functionalization starting from 10,15,20-meso-free 5-substituted porphyrin as building block is established. A meso-ABC–ABC-type meso–meso-linked donor–π-acceptor-type porphyrin dimer was prepared and exhibited the highest power conversion efficiency (7.91 %) ever reported for dye-sensitized solar cells based on dimeric orthogonal donor–π-acceptor-type organic sensitizers. This synthetic strategy will provide useful guidance for the rational design of functional porphyrin dimers and oligomers for diverse applications.     

Single-Pot Synthesis of Spiroannulated Dihydrofurans by Iodine–Ammonium Acetate–Mediated Reaction of Dimedone with Aldehydes

Iodine–ammonium acetate–mediated annealation of dimedone with aldehydes led to facile formation of spirodihydrofuran in good yields through tandem Knoevenagel–Michael iodonation and cyclodehydroiodonation reactions in a single pot.     

Photocatalytic C−H Functionalization of Nitrogen Heterocycles Mediated by a Redox Active Protecting Group

Herein, we report a photocatalytic strategy for the C−H functionalization of saturated azaheterocycles under mild conditions with only one equivalent of starting material. Our strategy is based on a redox active benzamide protecting group that is activated via a halogen-atom transfer (XAT) process to trigger the formation of an α-amino radical. This nucleophilic radical intermediate was then engaged in Giese additions and radical cross couplings to afford C−H alkylated and arylated products.     

Click Chemistry in Ultra-high Vacuum – Tetrazine Coupling with Methyl Enol Ether Covalently Linked to Si(001)

The additive-free tetrazine/enol ether click reaction was performed in ultra-high vacuum (UHV) with an enol ether group covalently linked to a silicon surface: Dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate molecules were coupled to the enol ether group of a functionalized cyclooctyne which was adsorbed on the silicon (001) surface via the strained triple bond of cyclooctyne. The reaction was observed at a substrate temperature of 380 K by means of X-ray photoelectron spectroscopy (XPS). A moderate energy barrier was deduced for this click reaction in vacuum by means of density functional theory based calculations, in good agreement with the experimental results. This UHV-compatible click reaction thus opens a new, flexible route for synthesizing covalently bound organic architectures.     

Three-component Oxytrifluoromethylation of Alkenes: Highly Efficient and Regioselective Difunctionalization of CC Bonds Mediated by Photoredox Catalysts

Here comes the sun: A facile vicinal difunctionalization of alkenes, oxytrifluoromethylation, was established by visible-light-driven photoredox catalysis. Judicious choice of the CF(3) source is key. Nucleophiles such as water, alcohols, and carboxylic acids can be used in this highly efficient (2-4?h) and regioselective (100?%) transformation using light-emitting diode (LED) lamps and natural sunlight. SET=single-electron transfer.     

On The Way to Fe–C60 Compounds

Iron: fullerides were prepared by chemical methodes in the solution using nitric acid as activation agent. Experimental results of thermal analyses, X-ray diffraction and Mössbauer spectroscopy of the products are presented. To interpret these results, standard quantum chemistry calculations were used to determine the geometry and charge distribution in Fe:C₆₀ complexes, which might be formed in the reaction.     

Formal Insertion of Alkenes Into C(sp3)−F Bonds Mediated by Fluorine-Hydrogen Bonding

C−F Insertion reactions represent an attractive approach to prepare valuable fluorinated compounds. The high strength of C−F bonds and the low reactivity of the fluoride released upon C−F bond cleavage, however, mean that examples of such processes are extremely scarce in the literature. Here we report a reaction system that overcomes these challenges using hydrogen bond donors that both activate C−F bonds and allow for downstream reactions with fluoride. In the presence of hexafluoroisopropanol, benzyl and propargyl fluorides undergo efficient formal C−F bond insertion across α-fluorinated styrenes. This process, which does not require any additional fluorinating reagent, occurs under mild conditions and delivers products featuring the gem-difluoro motif, which is attracting increasing interest in medicinal chemistry. Moreover, readily available organic bromides can be engaged directly in a one-pot process that avoids the isolation of organic fluorides.     

Covalently Linked at the Lower Rim Double‐Calix[4]arene as a Precursor for Multicavity Supramolecular Receptor

New covalently linked at the lower rim double‐calix[4]arens, which have great potential for the synthesis of multicavity receptors, were prepared via Sonogashira cross‐coupling reaction. The structures of 6 and 7 were confirmed by NMR, MS, and elemental analysis.