Why Static O-H Bond Parameters Cannot Characterize the Free Radical Scavenging Activity of Phenolic Antioxidants: ab initio Study

The static O-H bond parameters including O-H bond length, O-H charge difference, O-H Mulliken population and O-H bond stretching force constant (k) for 17 phenols were calculated by ab initio method HF/6-31G**. In combination with the O-H bond dissociation enthalpies (BDE) of the phenols determined by experiment, it was found that there were poor correlationships between the static O-H bond parameters and O-H BDE. Considering the good correlationship bt tween O-H BDE and logarithm of free radical scavenging rate constant for phenolic antioxidant, it is reasonable to believe that the ineffectiveness of static O-H bond parameters in characterizing antioxidant activity arises from the fact that they cannot measure the O-H BDE.

Visible-light-induced organocatalyzed C(sp^(2))–H bond functionalization of 1,3-azoles with trifluoroacetylsilanes

Previous carbene insertion to C–H bonds of 1,3-azoles relied on metal carbene species. Herein, we report a metal-free C(sp^(2))–H bond functionalization of 1,3-azoles with trifluoroacetylsilanes. The reaction features mild conditions, broad substrate scope and wide functional group tolerance. The mechanistic study supports that the success of the reaction is probably attributed to the dual roles of trifluoroacetylsilanes under the photocatalyzed conditions: generating carbenes which undergo cyclopropanation and generating biradicals which promote ring-opening aromatization of the in situ generated fused cyclopropanes.

Efficient Photolytic Halogenation and Oxidation of Unactivated Alkyl sp^(3) C—H Bonds with Iodine(III)

A metal-free,green,and sustainable functionalization of unactivated alkyl sp^(3) C—H bonds is reported using iodine(III)as a feasible dehydrogenation agent under visible light or KBr,and alkyl chlorides,bromides,alcohols,and ketones could be constructed by addition of different coupling reagents.Cheap and safe iodobenzene diacetate was used to form a radical to activate the alkyl sp^(3) C—H bond in a highly efficient manner,which can construct different alkylation products by adding corresponding coupling reagents.

Recent advances in the diversification of chromones and flavones by direct C-H bond activation or functionalization

Chromone and flavone are both central backbones of natural products and clinical medicines.Synthesis of diversely functionalized chromones and flavones constitutes significant research contents of the modern synthetic science because abundant molecular libraries of such types are crucial in providing candidate compounds for the discovery of new pharmaceuticals and functional materials.The direct C—H bond activation or functionalization on these heterocyclic backbones provides highly powerful tools for the rapid accesses to densely functionalized chromone and flavone derivatives.Considering the importance of the functionalized chromone and flavone compounds as well as the notable advances in the synthesis of such products by direct C—H activation or functionalization,we review herein the research advances in the C—H bond activation and functionalization reactions of chro mone and flavones,in hope of showing the current states and promise of the research domain.

A series of 3D lanthanide complexes based on H bond and halogen-halogen interactions：Synthesis, structure, spectroscopic and thermal properties

Four lanthanide coordination complexes, namely, [Ln（2,3-DClBA）3（5,5’-dmebipy）（H2O）]2（Ln=Sm（1）, Eu（2）, Dy（3）, Ho（4））; 2,3-DClBA=2,3-dichlorobenzoate; 5,5’-dmebipy=5,5’-dmethylbipyridine） were synthesized and characterized by elemental analysis, infrared spectroscopy and single crystal X-ray diffraction. Findings indicated that complex 3 was a dinuclear molecule, and the center Dy3＋ was eight-coordinated. Each dinuclear units could be connected by H bond and halogen-halogen interactions. Luminescent property of complex 2 suggested the typical intense emissions of Eu3＋ ions. Thermal analysis showed that the complexes decomposed in three steps： the coordination water was lost firstly then the neutral ligand 5,5’dmebipy was lost and lastly the 2,3-DClBA ligand was lost.

Palladium-Catalyzed Formal [4＋2] Cycloaddition of Benzoic and Acrylic Acids with 1,3-Dienes via C-H Bond Activation： Efficient Access to 3,4-Dihydroisocoumarin and 5,6-Dihydrocoumalins

We report a palladium-catalyzed formal intermolecular [4＋2] cycloaddition of benzoic and acrylic acids with 1,3-dienes including the stock chemicals 1,3-butadiene and isoprene leading to synthetically useful 3,4-dihydroisocoumarins and 5,6-dihydrocoumalins. Stepwise C-H bond cleavage and annulation are likely involved in the reaction pathway. The synthetic potential of the methodology was demonstrated by two short derivatizations and total synthesis of natural product Clausamine B.

Direct C-H Bond Activation of Benzoxazole and Benzothiazole with Aryl Bromides Catalyzed by Palladium（Ⅱ）-N-heterocyclic Carbene Complexes

Herein, we report that a series of novel palladium（II）-NHC complexes （NHC=N-heterocyclic carbene） were synthesized. The structures of all novel complexes were characterized by ^1H NMR, ^13C NMR, FT-IR spectroscopy and elemental analysis techniques. These palladium（ll）-NHC complexes were tested as efficient catalysts in the direct C-H bond activation of benzoxazole and benzothiazole with aryl bromides in the presence of 1 mol% catalyst loading at 150 ℃ for 4 h. Under the given conditions, various aryl bromides were successfully applied as the arylating reagents to achieve the 2-arylbenzoxazoles and 2-arylbenzothiazoles in acceptable to high yields.

C(sp^3)–H bond functionalization of non-cyclic ethers by decarboxylative oxidative coupling with α,β-unsaturated carboxylic acids

A copper-catalyzed decarboxylative oxidative coupling of α,β-unsaturated carboxylic acids with non-cyclic ethers is developed.This method provides a new approach for C(sp^3)–H bond functionalization of non-cyclic ethers. Mechanism study shows the reaction involves a radical process.

Enantioselective cyanation of benzylic C—H bonds via copper-catalyzed radical relay

With the support by the National Natural Science Foundation of China and the Chinese Academy of Sciences,the research team led by Prof.Liu Guosheng(刘国生)at Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences,and Prof.Shannon Stahl at the University of Wisconsin-Madison,discovered a copper-catalyzed radical relay pathway for enantioselective conversion of benzylic C—H bonds

A powerful approach to alkoxy radical-mediated remote C(sp^3)–H bonds functionalization

The activation of inert C（sp^3）–H bonds with control of reactivity and selectivity is one of the central topics in chemical sciences.

Neutral C–H bond vs. electron pair of N(sp^2): A binding site effect study of macrocycle anion receptor

To evaluate the effect of neutral C–H bond or electron pair of nitrogen atom with sp2hybridization（N（sp2）） involving into the same chemical environment for anion binding, two analogous tetracationic imidazolium macrocycles, namely cyclo[2]（2,6-bis-（1H-imidazol-1-yl）pyridine） [2]（1,3-dimethylenebenzene）（14＋）, and cyclo[2]（2,6-bis-（1H-imidazol-1-yl）pyridine）[2]（2,6-di methylenepyridine）（24＋）were studied in detail as small inorganic anion receptors. The guest anions with different shapes are Cl,N3, NO3, and H2PO4. The host–guest interactions were characterized via1 H NMR spectroscopy,electrospray ionization mass spectrometry（ESI-MS） and single crystal X-ray crystallography. The results implied that macrocyclic hosts with similar backbone but two distinct binding sites（14＋with neutral C–H vs. 24＋with N（sp2）） vary markedly in their response to anions, including the binding modes and association constants. The finding will serve to the construction of new anion receptors, even improve insights into the anion binding process in biology.

Recent advances in sulfenylation of C(sp^3)-H bond under transition metal-free conditions

In recent years,the transition metal-free sulfenylation of C-H bond for C-S formation has been rapidly advanced and has become an eco-friendly synthetic tool for pharmacists and organic chemists.Various natural or bioactive molecules such as(hetero)arenes,olefins,carbonyl compounds,alkanes,have been employed for sulfenylating reactions.This review will focus on the recent five-year advances in C-S bond formation via direct sulfenylation of C(sp^3)-H bonds under metal-free conditions and elaborate their mechanisms from a new perspective.

Synthesis and Crystal Structure of Zinc(II) Complex with Isonicotinate Containing a Three-dimensional Hydrogen-bond Network

A zinc complex, [Zn(iso)_2(H_2O)_4](iso=C_6H_4NO_2^-), was synthesized and characterized by elemental analysis, thermal analysis and IR spectrum studies. The crystal structure of the complex was determined by X-ray diffraction. The crystal crystallizes in the triclinic system, molecular formula ZnC12H16N2O8, Mr=381.64, space group P with a = 6.338(1), b =6.919(1), c=9.277(1), α=96.28(1), β=104.91(1), γ=112.85(1)°, V=352.12(9)?3, Z=1, Dc=1.80g?cm-3 and F(000)=196, μ =1.791mm-1. The crystal structure was solved by direct methods for final R=0.0204 and Rw=0.0542 for 1258 observed reflections with [Fo>4σ(Fo)]. The crystal structure reveals that zinc ion is trans-octahedral with two pyridyl nitrogens and two aque oxygens at the equational positions and two aqua oxygens at the axial positions. The complex forms a three-dimensional network through intermolecular hydrogen bonds.

Design and Synthesis of a Highly Stable Six-hydrogen-bonded Serfassembly Yellowish Green Electroluminescent Molecular Duplex

This paper describes the design, synthesis and characterization of a hydrogen-bonded molecular duplex with 1,8-naphthalimide fluorescent pendants. The two oligoamide molecular strands, with complementary hydrogen bond sequences of DDADAA and AADADD, can form an ultra stable self-assembly duplex. Its molecular structure was confu-med by ^1H NMR and ESI-MS, and its photoluminescence properties were determined. The resulting duplex exhibited a dramatically enhanced photoluminescence （PL） quantum efficiency of 63.7% compared to the corresponding 1,8-naphthalimide segment （32.4%）, suggesting that the formation of the duplex with larger molecular weight could successfully inhibit the quenching of the fluorescent pendant. This novel duplex is a prospective candidate for new electroluminescent emitter.

Structure and Fluorescence Property of a 2D Bilayer Cd(Ⅱ) Coordination Polymer Induced by H-bonding and π-π Interaction

Solvothermal reactions of 4,4＇-oxybis（benzoic acid） （H2oba） with 1,3-dipyridyl benzene （1,3-dpb） produced a two-dimensional （2D） cadmium（Ⅱ） coordination polymer {[Cd（oba）（dpb）]·H2O}n （1）. The complex was characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. It crystallizes in the monoclinic system, space group C2/c with a = 13.6692（9）, b = 25.9647（17）, c = 8.7912（6） , α = 125.0370（10）, γ = 2544.7（3）°, V = 2544.7（3） 3, C30H22N2O6Cd, Mr = 618.91, Dc =1.609 g/cm3, F（000） = 1248, μ = 0.904 mm-1 and Z = 4. The neighboring Cd（Ⅱ） ions are linked by oba2-anions and 1,3-dpb to form an infinitely 2D wavelike sheet, and two such 2D sheets are interlocked with each other by H-bonding to form a 2D → 2D structure. The adjacent two groups of interlocked structures are further linked to form a bilayer 2D supramolecular network by π-π interactions. In addition, the fluorescence property of 1 was also studied.

Novel four-hydrogen-bond assembled oligoamide dimer with pyrazoline moieties and its photoluminescent properties

In this paper, the synthesis and characterization of a triarylpyrazoline modified four-H-bonded molecular duplex are described. Its molecular structure has been confirmed by ^1H NMR and ESI-MS. The duplex emits strong pure blue light peaking at 448 and 452 nm under UV photoexcitation in solution and solid state, respectively, and its relative photoluminescence quantum efficiency in solution is determined as 0.778 using quinine sulfate as reference. In concentration of 〉40 mmol/L, the duplex can gelate DMSO, and the organogel formed shows good pure blue photoluminescence too. This novel duplex, for its well-defined structure and efficient photoluminescence property, is a prospective candidate for pure blue electroluminescent emitter.

Coordination of neighboring C——H bond to transition metal center——III. Study on localized molecular orbitals of the binucleate ion [Fe_2(CH_3)(CO) (Ph_2pCH_2PPh_2)Cp_2]^+

A localized INDO method was used to calculate the ion [Fe_2 (CH_3) (CO) (Ph_2PCH_2PPh_2)- Cp_2]^+. Based on the analysis of the localized molecular orbitals (LMO), bond orders and contour maps, it was pointed out that the LMO no. 20 corresponds to the coordination of C(1)-H(I) σbond to Fe(2) atom. Non occurrence of metal-metal bond between Fe(1) and Fe(2) atoms was found and the covalence of irons was numerated, which coincides with the value in ref 17.

Palladium-catalyzed late-stage mono-aroylation of the fully substituted pyrazoles via aromatic C-H bond activation

The palladium-catalyzed late-stage aroylation of 4-methyl-1,5-diaryl-lH-pyrazole-3-carboxylates has been developed via direct and exclusive mono-Csp^2-H bond activation with broad substrate scope and good functional group tolerance. A dual-core dimeric palladacycle is confirmed by X-ray single crystal crystallography, and probably serves as an active species in the catalytic cycle.

CONCERTED H-BONDING TEMPLATE SYNTHESIS OF AN ORDERED LADDER POLYSILSESQUIOXANE

A novel soluble regular ladder poly（benzoyl-3-aminopropyl） silsesquioxane （LPBAS） was facilely prepared under effective assistance of concerted H-bonding self-assembly of amido groups of side chains and silanol groups, respectively, of a new template monomer [1,3-bis（benzoyl-3-aminopropyl）-1,1,3,3-tetraethoxydisiloxane] （M）. The ordered ladder structure of LPBAS is manifested in： （1） the presence of two Bragg peaks representing the ladder width （d） and ladder thickness （t） in X-ray diffraction （XRD） pattern; （2） narrow base-line width （w = 6） of resonance absorption for -CH2SiO3/2 moiety in 29Si-NMR and （3） high glass transition temperature Tg = 1 12℃ in differential scanning calorimetry （DSC） analysis.