Synthesis of N,N′-Bis(arylsulfanyl)cyclohexa-2,5-diene-1,4-diimines and N,N′-(Cyclohexa-2,5-diene-1,4-diylidene)bis(arenesulfinamides)

Russian Journal of Organic Chemistry - Reactions of (chlorosulfanyl)benzenes with benzene-1,4-diamines afforded new N,N′-bis(arylsul­fanyl)cyclohexa-2,5-diene-1,4-diimines which were...     

Direct Cyclopropanation of α-Cyano β-Aryl Alkanes by Light-Mediated Single Electron Transfer Between Donor–Acceptor Pairs

Cyclopropanes are traditionally prepared by the formal [2+1] addition of carbene or radical based C1 units to alkenes. In contrast, the one-pot intermolecular cyclopropanation of alkanes by redox active C1 units has remained unrealised. Herein, we achieved this process simply by exposing β-aryl propionitriles and C1 radical precursors (N-oxy esters) to base and blue light. The overall process is redox-neutral and a photocatalyst, whether metal- or organic-based, is not required. Our findings support that single electron transfer (SET) from the α-cyano carbanion of the propionitrile to the N-oxy ester is facilitated by blue-light via their electron donor–acceptor (EDA) complex. The α-cyano carbon radical thus formed can then lose a β-proton to form a π-resonance stabilised radical anion that preferentially couples at the benzylic β-position with a decarboxylated C1 radical unit. This new transition metal-free chemistry tolerates both electron rich and electron deficient (hetero)aryl systems, even sulfide or alkene functionality, to afford a range of cis-aryl/cyano cyclopropanes bearing congested tetrasubstituted quaternary carbons.     

Spin–Orbit Charge-Transfer Intersystem Crossing (ISC) in Compact Electron Donor–Acceptor Dyads: ISC Mechanism and Application as Novel and Potent Photodynamic Therapy Reagents

Spin–orbit charge-transfer intersystem crossing (SOCT-ISC) is useful for the preparation of heavy atom-free triplet photosensitisers (PSs). Herein, a series of perylene-Bodipy compact electron donor/acceptor dyads showing efficient SOCT-ISC is prepared. The photophysical properties of the dyads were studied with steady-state and time-resolved spectroscopies. Efficient triplet state formation (quantum yield Φ_T=60 %) was observed, with a triplet state lifetime (τ_T=436 μs) much longer than that accessed with the conventional heavy atom effect (τ_T=62 μs). The SOCT-ISC mechanism was unambiguously confirmed by direct excitation of the charge transfer (CT) absorption band by using nanosecond transient absorption spectroscopy and time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The factors affecting the SOCT-ISC efficiency include the geometry, the potential energy surface of the torsion, the spin density for the atoms of the linker, solvent polarity, and the energy matching of the ¹CT/³LE states. Remarkably, these heavy atom-free triplet PSs were demonstrated as a new type of efficient photodynamic therapy (PDT) reagents (phototoxicity, EC₅₀=75 nm ), with a negligible dark toxicity (EC₅₀=78.1 μm ) compared with the conventional heavy atom PSs (dark toxicity, EC₅₀=6.0 μm, light toxicity, EC₅₀=4.0 nm ). This study provides in-depth understanding of the SOCT-ISC, unveils the design principles of triplet PSs based on SOCT-ISC, and underlines their application as a new generation of potent PDT reagents.     

Comparative matrix isolation infrared spectroscopy study of 1,3- and 1,4-diene monoterpenes (α-phellandrene and γ-terpinene)

In the present work, γ-terpinene (a 1,4-diene derivative) and α-phellandrene (1,3-diene derivative) were isolated in cryogenic argon matrices and their structures, vibrational spectra, and photochemistries were characterized with the aid of FTIR spectroscopy and quantum chemical calculations performed at the DFT/B3LYP/6-311++G(d,p) level of approximation. The molecules bear one conformationally relevant internal rotation axis, corresponding to the rotation of the isopropyl group. The calculations provide evidence of three minima on the potential energy surfaces of the studied molecules, where the isopropyl group assumes the trans, gauche+, and gauche- conformations (T, G+, G-). The signatures of all these conformers were identified in the experimental matrix infrared spectra, with the T forms dominating, in agreement with the theoretical predicted abundances in gas phase at room temperature. In situ UV (λ > 200 nm) irradiation of matrix-isolated α-phellandrene led to its isomerization into an open-ring species. The photoproduct was found to exhibit the ZE configuration of its backbone, which to be formed from the reactant molecule does not require extensive structural rearrangements of both the reagent and matrix. γ-Terpinene was photostable when subjected to irradiation under the same experimental conditions. In addition, the liquid compounds at room temperature were also investigated by FTIR-ATR and FT-Raman spectroscopies.     

Long-Lived Triplet Excited State Accessed with Spin–Orbit Charge Transfer Intersystem Crossing in Red Light-Absorbing Phenoxazine-Styryl BODIPY Electron Donor/Acceptor Dyads

Orthogonal phenoxazine-styryl BODIPY compact electron donor/acceptor dyads were prepared as heavy atom-free triplet photosensitizers (PSs) with strong red light absorption (ϵ=1.33×10⁵ M⁻¹ cm⁻¹ at 630 nm), whereas the previously reported triplet photosensitizers based on the spin-orbit charge transfer intersystem crossing (SOCT-ISC) mechanism show absorption in a shorter wavelength range (<500 nm). More importantly, a long-lived triplet state (τ_T=333 μs) was observed for the new dyads. In comparison, the triplet state lifetime of the same chromophore accessed with the conventional heavy atom effect (HAE) is much shorter (τ_T=1.8 μs). Long triplet state lifetime is beneficial to enhance electron or energy transfer, the primary photophysical processes in the application of triplet PSs. Our approach is based on SOCT-ISC, without invoking of the HAE, which may shorten the triplet state lifetime. We used bisstyrylBodipy both as the electron acceptor and the visible light-harvesting chromophore, which shows red-light absorption. Femtosecond transient absorption spectra indicated the charge separation (109 ps) and SOCT-ISC (charge recombination, CR; 2.3 ns) for BDP-1 . ISC efficiency of BDP-1 was determined as Φ_T=25 % (in toluene). The dyad BDP-3 was used as triplet PS for triplet-triplet annihilation upconversion (upconversion quantum yield Φ_UC=1.5 %; anti-Stokes shift is 5900 cm⁻¹).     

Geometrical Changes and Their Energies in the Formation of Donor–Acceptor Complexes

We have mapped the energy demands of the geometrical changes in donor–acceptor complexes BH₃NH₃ and AlCl₃NH₃ and in the course of their formation from their monomers. We have varied the individual geometrical parameters systematically and performed ab initio quantum chemical calculations for these structures. We investigated the energy requirements to change bond lengths and bond angles in both the monomers and complexes and the angles of torsion in the complexes. The changes of bond lengths require more energy in the monomers than in the complexes. The energies to change the acceptor bond angles in the monomers are markedly higher than in the complexes. The changes in the geometrical parameters during the complexation process are more moderate in donors than in acceptors, in agreement with prior experimental observations. The geometry versus energy variations related to the process of complexation are in agreement with the notion of relative rigidity of the donor parts and the more compliant nature of the acceptor parts as well as with the notion of competing effects in the structures of the complexes.     

Photobase-Driven Excited-State Intramolecular Proton Transfer (ESIPT) in a Strapped π-Electron System

We report a new design strategy for an excited-state intramolecular proton transfer (ESIPT) fluorophore that can be used in acidic media. A photobasic pyridine-centered donor-acceptor-donor-type fluorophore is combined with a basic trialkylamine “strap”. In the presence of an acid, protonation occurs predominantly at the amine moiety in the ground state. A single-crystal X-ray diffraction analysis confirmed the formation of a pre-organized intramolecular hydrogen-bonded structure between the resulting ammonium moiety and the pyridine ring. Upon excitation, the intramolecular charge-transfer transition increases the basicity of the pyridine moiety in the excited state, resulting in proton transfer from the amine to the pyridine moiety. Consequently, the fluorophore takes on a polymethine-dye character in the ESIPT state, which gives rise to significantly red-shifted emission with an increased fluorescence quantum yield.     

Enhanced Light-Driven Hydrogen-Production Activity Induced by Accelerated Interfacial Charge Transfer in Donor–Acceptor Conjugated Polymers/TiO2 Hybrid

Donor–acceptor (D–A) conjugated polymers have proved to be desired candidates to couple with inorganic semiconductors for enhanced photocatalytic activity. Herein, the matched energy levels between polymer BFB and TiO₂ make them form BFB-TiO₂ composites with moderate photocatalytic H₂ evolution rate (HER). To further enhance the interfacial interaction, BFB was modified with a carboxylic acid end group, which reacted with surface OH of TiO₂ to form an ester bond. As a result, the functionalized BFBA-TiO₂ composites exhibited superior photocatalytic activity. Especially, HER of 4 % BFBA-TiO₂ can reach up to 228.2 μmol h⁻¹ under visible light irradiation (λ>420 nm), which is about 2.02 times higher than that of BFB-TiO₂. The enhanced photocatalytic activity originated from the formed ester bond between polymer and TiO₂, and photogenerated electrons injection from lowest unoccupied molecular orbital (LUMO) of the exited polymer to conduction band of TiO₂ were accelerated. Therefore, based on an intermolecular interaction mechanism, more suitable D–A conjugated polymers with anchoring groups could be designed to couple with other semiconductors for enhancing photocatalytic activity.     

Porphyrin–Fullerene Dyad Based on Indium(III) Complex. Donor–Acceptor Complex Formation Equilibrium

Formation kinetics and spectral properties of the donor–acceptor complexes of (5,10,15,20- tetra(2-methoxyphenyl)porphinato)chloroindium(III) with 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin- 2-yl)methylpyrrolidinyl[3′,4′:1,2][60]fullerene were studied. The formation of the donor–acceptor dyad [(Py₃F)InTPP(2-OCH₃)₄]⁺Cl^– occurs as a two-step reaction, including fast reversible coordination of the fullerene base molecule and slow irreversible displacement of the axial chloride ion to the second coordination sphere. Quantitative characteristics for the reaction rate and equilibrium were obtained. The reaction products were identified by IR and ¹H NMR spectroscopy. The most important electron optical and stability parameters of the porphyrin–fullerene dyads with inner- and outer-sphere chloride ions were determined. These results are important for studies of the photophysics of porphyrin–fullerene dyads and development of photoconverters based on them.     

Photoinduced Electron Transfer (PET) between C_(60) and Amines in Micelle Solution A Kinetic ESR Study

Fullerene chemistry has been one of the most exciting research subjects in the recent decade1,2. However, the predominant hydrophobic character and the spherical carbon allotrope of C60 hinder its solubility in an aqueous solution. In order to efficiently slow down charge recombination in the PET system containing C60, water was selected as optimal polar media to stabilize charge separation state. Accordingly, solubility of fullerene in water had to be achieved by incorporating it into th…     

Influence of Metal–Peptide Complexation on Fragmentation and Inter-Fragment Hydrogen Migration in Electron Transfer Dissociation

The use of metal salts in electrospray ionization (ESI) of peptides increases the charge state of peptide ions, facilitating electron transfer dissociation (ETD) in tandem mass spectrometry. In the present study, K⁺ and Ca²⁺ were used as charge carriers to form multiply-charged metal–peptide complexes. ETD of the potassium- or calcium-peptide complex was initiated by transfer of an electron to a proton remote from the metal cation, and a c'-z? fragment complex, in which the c' and z? fragments were linked together via a metal cation coordinating with several amino acid residues, was formed. The presence of a metal cation in the precursor for ETD increased the lifetime of the c'-z? fragment complex, eventually generating c? and z' fragments through inter-fragment hydrogen migration. The degree of hydrogen migration was dependent on the location of the metal cation in the metal-peptide complex, but was not reconciled with conformation of the precursor ion obtained by molecular mechanics simulation. In contrast, the location of the metal cation in the intermediate suggested by the ETD spectrum was in agreement with the conformation of “proton-removed” precursors, indicating that the charge reduction of precursor ions by ETD induces conformational rearrangement during the fragmentation process.

Geometrically Compelled Silicon(II)/Silicon(IV) Donor–Acceptor Interaction Enables the Enamination of Nitriles

Discovering new bonding scenarios and subsequently exploring the reactivity contribute substantially to advance the main group element chemistry. Herein, we report on the isolation and characterization of an intriguing class of the hydrido-benzosiloles 2 – 4 . These compounds exhibit a side arm of the amidinatosilylenyl group, featuring unidirectional silicon(II)/silicon(IV) donor-acceptor interaction on account of the geometric constraint. Furthermore, the reactions involving 2 – 4 with nitriles yield the tricyclic compounds that edge-fused of the Si-heteroimidazolidine-CN₂Si₂, silole-C₄Si, and phenyl-C₆-rings ( 5 – 13 ). These compounds are manifesting a unique reaction that the silicon(II)/silicon(IV) interaction enables the enamination of the α-H-bearing nitriles. The reaction mechanism involved in H-shift under oxidative addition at silylene followed by hydrosilylation of a ketenimine intermediate was revealed by density function theory (DFT) calculations.     

2,5-二(2-羟乙氨基)-1,4-苯醌合成方法的改进

以对苯二酚和乙醇胺为原料,直接合成2,5-二(2-羟乙氨基)-1,4-苯醌,并对产物进行红外、紫外、质谱及核磁表征.采用正交设计法对实验条件进行优化,乙醇为溶剂,对苯二酚和乙醇胺物质的量比为1∶5,在50℃下,反应2h,最高产率达到72.8%.产物为针状晶体,纯度较高.     

Suzuki–Miyaura reactions of the bis(triflates) of 1,3- and 1,4-dihydroxythioxanthone. Electronic and steric effects on the site-selectivity

The palladium(0)-catalyzed Suzuki cross-coupling reactions of the bis(triflates) of 1,3- and 1,4-dihydroxythioxanthone afforded various aryl-substituted thioxanthones. While the Suzuki reactions of the bis(triflate) derived from 1,3-dihydroxythioxanthone proceeded by site-selective attack in favor of position 3, the reactions of the bis(triflate) of 1,4-dihydroxythioxanthone proceeded in favor of position 1. The site-selectivity is controlled by steric and electronic parameters.     

Stepwise Mechanism of the Rhenium(V) Porphyrin Reaction with Pyridine,and the Chemical Structure of the Donor–Acceptor Complex

Russian Journal of Physical Chemistry A - Chemical thermodynamics and UV, visible, IR, 1H NMR, and mass spectrometry are used to study the complex reaction of...     

Synthesis of chiral 1- and 2-(p-tolylsulfinyl)-3-trimethylsilyloxybuta-1,3-dienes and their behaviour in Diels–Alder cycloadditions

The synthesis of (±)-(E)-1-(p-tolylsulfinyl)-3-trimethylsilyloxybuta-1,3-diene 1 and (S_S)-2-(p-tolylsulfinyl)-3-trimethylsilyloxybuta-1,3-diene 2 and their reactions with cyclic dienophiles are described. Cycloaddition of diene 1 with N-methylmaleimide 10 was performed under pressure affording a complex reaction mixture from which two epimers at C-3′, (±)-11a and (±)-11b [2,3,3a,4,5,7a-hexahydro-2-methyl-7a-(1-methylsuccinimide-3-yl)-1H-isoindole-1,3,5-triones], were isolated in equal amounts. Diene (±)-1 cycloadded to the more reactive 4-methyl-1,2,4-triazoline-3,5-dione 14 at atmospheric pressure and room temperature. However, nothing can be said about the stereochemical outcome of this addition since the loss of the chiral auxiliary via the sulfoxide–sulfenate rearrangement gave the bicyclic α,β-unsaturated ketone 17 (2-methyl-2,3,5,6-tetrahydro-1H-[1,2,4]triazolo[1,2-a]pyridazine-1,3,6-trione). Diels–Alder cycloaddition of enantiopure diene 2 with 10 occurred under pressure leading to a diastereomeric mixture of adducts where the trimethylsilyl enol ether moiety spontaneously evolved to the ketone function. The major enantiopure product 18a [(3aS,6S,7aR,R_S)-2-methyl-6-(p-tolylsulfinyl)perhydroisoindole-1,3,5-trione] was isolated and characterized. Cycloadditions of both dienes to dienophile 10 appear highly stereoselective.     

Synthesis and Crystal Structure of 2-(Diphenylphosphine oxide)-3-(diphenylphosphine oxide ethynyl) spiro [bicyclo[2.2.1]hepta-2,5-diene-7,1''''-cyclopropane]

1 INTRODUCTION Organic phosphine compounds always attract great interest for their unique properties and extensive uses in biochemistry, pesticide chemistry and synthetic organic chemistry. In the last two decades, much attention has been paid to phosphorus-containing olefin and acetylenic compounds for their applications in transition metal chemistry, asymmetric catalysis and photorearrang- ement [1~7 ]. Previously, we have reported the crystal structure of a novel host compound which …     

Coordination Sphere Tuning of the Electron Transfer Dissociation Behavior of Cu(II)–Peptide Complexes

In contrast to previous electron capture dissociation (ECD) studies, we find that electron transfer dissociation (ETD) of Cu(II)–peptide complexes can generate c- and z-type product ions when the peptide has a sufficient number of strongly coordinating residues. Double-resonance experiments, ion-molecule reactions, and collision-induced dissociation (CID) prove that the c and z product ions are formed via typical radical pathways without the associated reduction of Cu(II), despite the high second ionization energy of Cu. A positive correlation between the number of Cu(II) binding groups in the peptide sequence and the extent of c and z ion formation was also observed. This trend is rationalized by considering that the recombination energy of Cu(II) can be lowered by strong binding ligands to an extent that enables electron transfer to non-Cu sites (e.g., protonation sites) to compete with Cu(II) reduction, thereby generating c/z ions in a manner similar to that observed for protonated (i.e., nonmetalated) peptides.     

2,5-二叔丁基-1,4-二(对苯甲酸氧基)苯的合成与表征

4-氟苯腈和2,5-二叔丁基对苯二酚亲核取代反应合成2,5-二叔丁基-1,4-二（对苯腈氧基）苯（产率87.00%,白色晶体,mp280℃）,然后将二腈在碱性条件下水解,合成了1种分子中同时含有2个醚键和2个叔丁基的芳香族二酸--2,5-二叔丁基-1,4-二（对苯甲酸氧基）苯（产率72.78%,白色针状晶体,mp＞340℃）。产物经元素分析和IR、¹H NMR、¹³C NMR和MS波谱表征确证。