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2017 Volume 75 Issue 12
2017, 75(12): 1137-1149
doi: 10.6023/A17080384
Abstract:
Nitrogen-centered radicals are highly reactive intermediates, which provide new opportunities for designing new chemical reactions and preparing nitrogen-containing molecules. Direct generation of nitrogen-centered radicals via activation of N-H bonds under photocatalytic conditions has emerged as a green, efficient, and economical process, where significant progress has been made with methodology development in very recent years. In this paper, we highlight the important advances in this area that were reported since 2016.
Nitrogen-centered radicals are highly reactive intermediates, which provide new opportunities for designing new chemical reactions and preparing nitrogen-containing molecules. Direct generation of nitrogen-centered radicals via activation of N-H bonds under photocatalytic conditions has emerged as a green, efficient, and economical process, where significant progress has been made with methodology development in very recent years. In this paper, we highlight the important advances in this area that were reported since 2016.
2017, 75(12): 1150-1163
doi: 10.6023/A17090440
Abstract:
Circularly polarized luminescence (CPL) not only can reflect the excited state structure information of chiral system, but also has wide potential applications in 3D display, communication of spin information, information storage and processing, CPL laser and biological probe. Consequently, more and more attention and interests have been attracted into this field, which turns to be one of the most hot topics in organic luminescence materials in recent years. In this review, recent progress on the chiral organic small molecules with CPL properties is summarized. First, CPL concept and earlier studies of CPL and organic small molecules with CPL properties are briefly introduced. Then, chiral organic small molecules with CPL properties are classified into four types of central chirality, axial chirality, planar chirality, and helical chirality, and their progresses in recent years are systematically described, respectively. Among the small molecular systems with different types of chirality, those ones based on the biaryl skeleton and helicene derivatives show excellent CPL properties, and they could also be controlled or switched by anions, protons and others. Moreover, it should be paid attention to the applications of aggregation induced effect (AIE) and supramolecular chemistry for the chiral organic small molecules to obtain better CPL property. Finally, a conclusion and perspective on CPL materials based on chiral small molecules is provided.
Circularly polarized luminescence (CPL) not only can reflect the excited state structure information of chiral system, but also has wide potential applications in 3D display, communication of spin information, information storage and processing, CPL laser and biological probe. Consequently, more and more attention and interests have been attracted into this field, which turns to be one of the most hot topics in organic luminescence materials in recent years. In this review, recent progress on the chiral organic small molecules with CPL properties is summarized. First, CPL concept and earlier studies of CPL and organic small molecules with CPL properties are briefly introduced. Then, chiral organic small molecules with CPL properties are classified into four types of central chirality, axial chirality, planar chirality, and helical chirality, and their progresses in recent years are systematically described, respectively. Among the small molecular systems with different types of chirality, those ones based on the biaryl skeleton and helicene derivatives show excellent CPL properties, and they could also be controlled or switched by anions, protons and others. Moreover, it should be paid attention to the applications of aggregation induced effect (AIE) and supramolecular chemistry for the chiral organic small molecules to obtain better CPL property. Finally, a conclusion and perspective on CPL materials based on chiral small molecules is provided.
2017, 75(12): 1164-1172
doi: 10.6023/A17070341
Abstract:
Temperature is a basic physical parameter. Accurate measurement of temperature is of importance to scientific research and to industry production and life. Fluorescent temperature sensing, as a new method for temperature measurement, has received much attention because of its high resolution, fast response and observation with bear eyes, etc. Organic fluorescence probes are firstly used in fluorescent temperature sensing due to the versatility of structures, easier modification, and the consequent multiple spectral responses. The fluorescent thermometers can be applied in the temperature sensing of large area, microfluids, biological systems and so on, which make them attractive in the field of fluorescent probes research. In recent years, fluorescent thermometers based on organic fluorescence probes have made remarkable progress. Two major kinds of organic fluorescence thermometers are classified in this review based on the response of fluorescence wavelength, one is the single-wavelength response type, and the other is the ratiometric one. For the single-wavelength type, there are thermal-quenching and thermal-enhancing fluorescence thermometers based on the temperature-dependent trend of emission intensity. At the earlier stage, organic chromophores with high fluorescence quantum yields are adopted as the thermal quenching fluorescence thermometer, and recently a series of conformation-regulated organic thermometers based on dendritic structure and aggregation-induced emission chromophore was developed. Thermal response macromolecules including PNIPAM, PEG and DNA are widely used to create thermal responsive microenvironment to regulate chromophore emission, and then develop thermal-enhancing fluorescence thermometers. Ratiometric fluorescence thermometers show better sensitivity and accuracy than single-wavelength ones due to their self-correction property based on the different thermal-response of emission at two wavelengths. Several kinds of ratiometric sensing systems have been developed, which are based on dye-copolymerized/doped polymer systems, monomer-excimer ratiometric emission, chromophores with thermal transition of local excited state and twisted intramolecular charge transfer state, and chromophores with thermal-induced crystal transfer. In this review, recent advances of organic fluorescence thermometers mentioned above will be presented and the challenges and the future development will be discussed.
Temperature is a basic physical parameter. Accurate measurement of temperature is of importance to scientific research and to industry production and life. Fluorescent temperature sensing, as a new method for temperature measurement, has received much attention because of its high resolution, fast response and observation with bear eyes, etc. Organic fluorescence probes are firstly used in fluorescent temperature sensing due to the versatility of structures, easier modification, and the consequent multiple spectral responses. The fluorescent thermometers can be applied in the temperature sensing of large area, microfluids, biological systems and so on, which make them attractive in the field of fluorescent probes research. In recent years, fluorescent thermometers based on organic fluorescence probes have made remarkable progress. Two major kinds of organic fluorescence thermometers are classified in this review based on the response of fluorescence wavelength, one is the single-wavelength response type, and the other is the ratiometric one. For the single-wavelength type, there are thermal-quenching and thermal-enhancing fluorescence thermometers based on the temperature-dependent trend of emission intensity. At the earlier stage, organic chromophores with high fluorescence quantum yields are adopted as the thermal quenching fluorescence thermometer, and recently a series of conformation-regulated organic thermometers based on dendritic structure and aggregation-induced emission chromophore was developed. Thermal response macromolecules including PNIPAM, PEG and DNA are widely used to create thermal responsive microenvironment to regulate chromophore emission, and then develop thermal-enhancing fluorescence thermometers. Ratiometric fluorescence thermometers show better sensitivity and accuracy than single-wavelength ones due to their self-correction property based on the different thermal-response of emission at two wavelengths. Several kinds of ratiometric sensing systems have been developed, which are based on dye-copolymerized/doped polymer systems, monomer-excimer ratiometric emission, chromophores with thermal transition of local excited state and twisted intramolecular charge transfer state, and chromophores with thermal-induced crystal transfer. In this review, recent advances of organic fluorescence thermometers mentioned above will be presented and the challenges and the future development will be discussed.
2017, 75(12): 1173-1182
doi: 10.6023/A17090419
Abstract:
Bioorthogonal reactions enable us to study and manipulate biological processes under living conditions. As widely used and powerful tools, biorthogonal reactions are largely defined as "ligation reactions" that are used for labeling, tracing and capturing biomolecules. Recently, an emerging collection of biorthogonal "bond-cleavage reactions" have been developed and applied for biological studies, especially in releasing, activating and manipulating biomolecules. In this review, we will first summarize the characteristics and applications of these biorthogonal cleavage reactions. We will then focus on introducing diverse applications of biorthogonal cleavage reactions, including activation of prodrugs, rescue of intracellular protein activity, engineering of cell surface, among other interesting applications. Finally, the outlook of future development and applications of biorthogonal cleavage reactions will be discussed.
Bioorthogonal reactions enable us to study and manipulate biological processes under living conditions. As widely used and powerful tools, biorthogonal reactions are largely defined as "ligation reactions" that are used for labeling, tracing and capturing biomolecules. Recently, an emerging collection of biorthogonal "bond-cleavage reactions" have been developed and applied for biological studies, especially in releasing, activating and manipulating biomolecules. In this review, we will first summarize the characteristics and applications of these biorthogonal cleavage reactions. We will then focus on introducing diverse applications of biorthogonal cleavage reactions, including activation of prodrugs, rescue of intracellular protein activity, engineering of cell surface, among other interesting applications. Finally, the outlook of future development and applications of biorthogonal cleavage reactions will be discussed.
2017, 75(12): 1183-1195
doi: 10.6023/A17060284
Abstract:
The electrolyte is an indispensable constituent in lithium ion batteries, and its role conducts electricity by means of the transportation of charge carries between the pair of electrodes. Its properties directly affect the energy density, cycle life and safety of the battery. However, there are two major challenges to using carbonate-based electrolytes in recent lithium ion batteries (LIBs) to further increase the energy density of the devices without compromising the safety. One is that carbonate-based electrolytes are not sufficiently stable at the positive electrode, and the other is their relatively high flammability. Therefore, developing high voltage and flame retardant electrolytes for LIBs is highly desired. Herein, we review the recent progress and challenges in new electrolytes, focusing on high-voltage electrolytes, flame retardant electrolytes and highly concentrated electrolytes. Among the reported electrolytes, highly concentrated electrolytes are worth a special attention, showing various unusual functionalities, for example, high oxidative stability, low volatility, high reductive stability, and non-corrosive to Al. These special properties are totally different from that of the conventional 1 mol•L-1 LiPF6/EC-based electrolytes, which are result from solution structures. A discussion is also provided in this review on the prospects of further development of new electrolytes for LIBs.
The electrolyte is an indispensable constituent in lithium ion batteries, and its role conducts electricity by means of the transportation of charge carries between the pair of electrodes. Its properties directly affect the energy density, cycle life and safety of the battery. However, there are two major challenges to using carbonate-based electrolytes in recent lithium ion batteries (LIBs) to further increase the energy density of the devices without compromising the safety. One is that carbonate-based electrolytes are not sufficiently stable at the positive electrode, and the other is their relatively high flammability. Therefore, developing high voltage and flame retardant electrolytes for LIBs is highly desired. Herein, we review the recent progress and challenges in new electrolytes, focusing on high-voltage electrolytes, flame retardant electrolytes and highly concentrated electrolytes. Among the reported electrolytes, highly concentrated electrolytes are worth a special attention, showing various unusual functionalities, for example, high oxidative stability, low volatility, high reductive stability, and non-corrosive to Al. These special properties are totally different from that of the conventional 1 mol•L-1 LiPF6/EC-based electrolytes, which are result from solution structures. A discussion is also provided in this review on the prospects of further development of new electrolytes for LIBs.
2017, 75(12): 1196-1201
doi: 10.6023/A17080372
Abstract:
The asymmetric carbonyl allylation of aldehydes with allylmetal reagents presents one of the most efficient and straightforward methods for the synthesis of optically active homoallylic alcohols, which have found widespread applications in organic synthesis. As such, a wide range of chiral catalysts, including Lewis acids, Lewis bases and Br nsted acids have been reported to enable highly stereoselective carbonyl allylation of aldehydes with allylmetal reagents. Among them, chiral phosphoric acid-catalyzed carbonyl allylation of aldehydes with pinacol allylboronates represents a promising method, whereas an additional operations required for the preparation of allylboronates from allyl halides or highly active allylmetallics impose some constraints on the carbonyl allylation process. In this context, the asymmetric addition of allylboronates, in situ generated from palladium-catalyzed allylborylation, to aldehydes has been reported, while stoichiometric amounts of chiral diboronate reagents are basically required. Allylic alcohols are readily available feedstock. The direct use of allylic alcohols as starting materials in asymmetric allylborylation of carbonyls is highly valuable. Herein, we will report an asymmetric carbonyl allylation of aldehydes with allylic alcohols in the presence of octamethyl-2, 2'-bi(1, 3, 2-dioxaborolane) under the sequential catalysis of a palladium complex and chiral phosphoric acid. The presence of 2.5 mol% (η3-C3H5)2Pd2Cl2, 5 mol% P(OPh)3 and 10 mol% chiral phosphoric acid B*H-1 enabled 4-nitrobenzaldehyde 2a to smoothly undergo the asymmetric carbonyl allylation reaction with 2-buten-1-ol 1a and octamethyl-2, 2'-bi(1, 3, 2-dioxaborolane), giving rise to the desired homoallylic alcohol product 3aa in a 99% yield and with >20:1 dr and 92% ee. Under the optimal conditions, the generality for allylic alcohol substrates was investigated to reveal that the installation of either of saturated alkyl substituents, carbon-carbon double bond or heteroatom group in the allylic alcohols allowed the target products (3ca~3fa, 3ha~3ja) to be obtained in high yields and with excellent stereoselectivities. A (Z)-allylic alcohol and branched allylic alcohols were also able to generate the target products (3ba, 3ga), successfully. Although cinnamic alcohols participated in a clean reaction, relatively lower yields and stereoselectivity were delivered (3ka and 3la). The examination of aldehydes suggested that the introduction of either electronically deficient or rich substituents to the benzene ring of benzaldehydes was tolerant and led to corresponding homoallylic alcohols in excellent yields and stereoselectivities (3ab~3ak and 3m), with the exception of o-anisaldehyde (3al). In addition, 2-naphthaldehyde, aliphatic aldehydes and enals are all good substrates and provide high yields and enantiomeric excesses as exemplified by 3-phenylpropanal and 4-methoxycinnamaldehyde (3an~3ap).
The asymmetric carbonyl allylation of aldehydes with allylmetal reagents presents one of the most efficient and straightforward methods for the synthesis of optically active homoallylic alcohols, which have found widespread applications in organic synthesis. As such, a wide range of chiral catalysts, including Lewis acids, Lewis bases and Br nsted acids have been reported to enable highly stereoselective carbonyl allylation of aldehydes with allylmetal reagents. Among them, chiral phosphoric acid-catalyzed carbonyl allylation of aldehydes with pinacol allylboronates represents a promising method, whereas an additional operations required for the preparation of allylboronates from allyl halides or highly active allylmetallics impose some constraints on the carbonyl allylation process. In this context, the asymmetric addition of allylboronates, in situ generated from palladium-catalyzed allylborylation, to aldehydes has been reported, while stoichiometric amounts of chiral diboronate reagents are basically required. Allylic alcohols are readily available feedstock. The direct use of allylic alcohols as starting materials in asymmetric allylborylation of carbonyls is highly valuable. Herein, we will report an asymmetric carbonyl allylation of aldehydes with allylic alcohols in the presence of octamethyl-2, 2'-bi(1, 3, 2-dioxaborolane) under the sequential catalysis of a palladium complex and chiral phosphoric acid. The presence of 2.5 mol% (η3-C3H5)2Pd2Cl2, 5 mol% P(OPh)3 and 10 mol% chiral phosphoric acid B*H-1 enabled 4-nitrobenzaldehyde 2a to smoothly undergo the asymmetric carbonyl allylation reaction with 2-buten-1-ol 1a and octamethyl-2, 2'-bi(1, 3, 2-dioxaborolane), giving rise to the desired homoallylic alcohol product 3aa in a 99% yield and with >20:1 dr and 92% ee. Under the optimal conditions, the generality for allylic alcohol substrates was investigated to reveal that the installation of either of saturated alkyl substituents, carbon-carbon double bond or heteroatom group in the allylic alcohols allowed the target products (3ca~3fa, 3ha~3ja) to be obtained in high yields and with excellent stereoselectivities. A (Z)-allylic alcohol and branched allylic alcohols were also able to generate the target products (3ba, 3ga), successfully. Although cinnamic alcohols participated in a clean reaction, relatively lower yields and stereoselectivity were delivered (3ka and 3la). The examination of aldehydes suggested that the introduction of either electronically deficient or rich substituents to the benzene ring of benzaldehydes was tolerant and led to corresponding homoallylic alcohols in excellent yields and stereoselectivities (3ab~3ak and 3m), with the exception of o-anisaldehyde (3al). In addition, 2-naphthaldehyde, aliphatic aldehydes and enals are all good substrates and provide high yields and enantiomeric excesses as exemplified by 3-phenylpropanal and 4-methoxycinnamaldehyde (3an~3ap).
2017, 75(12): 1202-1206
doi: 10.6023/A17100448
Abstract:
Halohydrins bearing a hydroxyl and halide functional group, are privileged building blocks in organic synthesis and could be conveniently converted to other significant organic intermediates such as azidoalcohols, aminoalcohols, and epoxides, all of which are widely used in the synthesis of highly value-added chemicals. Among the approaches to halohydrins, the halohydroxylation of olefins provides a direct and efficient approach. The synthesis of bromohydrins has achieved great progress in recent years. However, the approaches to iodohydrins are still very limited. Our previous studies revealed that DMSO could oxidize halo anions to halo cations under acidic conditions. As our continuous development DMSO-based reactions, we report the iodohydroxylation of olefins by using DMSO and HI generated in situ. In this transformation, DMSO performed versatile roles as an oxidant, a solvent and an oxygen source. This reaction featured with simple operation, mild reaction condition, and wild substrate scope, and provided an efficient method to synthesize iodohydrins. Furthermore, the iodoetheration of olefins was also realized by using DMSO and alcohol as the solvent. A representative procedure for this reaction is as following:The mixture of alkene (0.5 mmol), NaI (0.6 mmol), conc. H2SO4 (1.0 mmol), DMSO (1 mL) and DCE (1 mL) were stirred at 60℃ under air. TCL monitor the reaction, and the product had a clear spot in phosphomolybdic acid chromogenic agent. After the reaction was completed, saturated solution of Na2S2O3 (0.5 mL) was added into the system to consume the extra I2. After cooling down to room temperature, the mixture was diluted with water (10 mL) and extracted with ethyl acetate (10 mL×3). The combined organic extract was washed with saturated solution of NaCl (15 mL), dried over MgSO4, and evaporated in vacuo. The residue was purified by chromatography on silica gel (petroleum ether/ethyl acetate) to afford the desired product.
Halohydrins bearing a hydroxyl and halide functional group, are privileged building blocks in organic synthesis and could be conveniently converted to other significant organic intermediates such as azidoalcohols, aminoalcohols, and epoxides, all of which are widely used in the synthesis of highly value-added chemicals. Among the approaches to halohydrins, the halohydroxylation of olefins provides a direct and efficient approach. The synthesis of bromohydrins has achieved great progress in recent years. However, the approaches to iodohydrins are still very limited. Our previous studies revealed that DMSO could oxidize halo anions to halo cations under acidic conditions. As our continuous development DMSO-based reactions, we report the iodohydroxylation of olefins by using DMSO and HI generated in situ. In this transformation, DMSO performed versatile roles as an oxidant, a solvent and an oxygen source. This reaction featured with simple operation, mild reaction condition, and wild substrate scope, and provided an efficient method to synthesize iodohydrins. Furthermore, the iodoetheration of olefins was also realized by using DMSO and alcohol as the solvent. A representative procedure for this reaction is as following:The mixture of alkene (0.5 mmol), NaI (0.6 mmol), conc. H2SO4 (1.0 mmol), DMSO (1 mL) and DCE (1 mL) were stirred at 60℃ under air. TCL monitor the reaction, and the product had a clear spot in phosphomolybdic acid chromogenic agent. After the reaction was completed, saturated solution of Na2S2O3 (0.5 mL) was added into the system to consume the extra I2. After cooling down to room temperature, the mixture was diluted with water (10 mL) and extracted with ethyl acetate (10 mL×3). The combined organic extract was washed with saturated solution of NaCl (15 mL), dried over MgSO4, and evaporated in vacuo. The residue was purified by chromatography on silica gel (petroleum ether/ethyl acetate) to afford the desired product.
2017, 75(12): 1207-1214
doi: 10.6023/A17050220
Abstract:
With Prussian blue (PB) as the precursor for γ-Fe2O3, the tri-component CdS/RGO/γ-Fe2O3 photocatalyst was prepared through loading PB nanocubes and CdS nanoparticles on graphene oxide (GO) nanosheets, followed by a calcination process in inert atmosphere (N2). The content of γ-Fe2O3 in the CdS/RGO/γ-Fe2O3 photocatalyst can be adjusted by changing the loading amount of PB, and the cubic morphology of PB was maintained after the calcination. The composition, structure, morphology and light absorption of the as-prepared products were investigated by X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (FT-IR), Raman spectroscopy and ultraviolet-visible (UV-vis) spectroscopy. The photocatalytic activity of the ternary photocatalysts was evaluated by the degradation of the organic pollutant of Rhodamine B (RhB) under visible-light irradiation. It was found that the degradation process of RhB follows pseudo-first-order kinetics. Compared to the bi-component CdS/RGO photocatalyst, the tri-component CdS/RGO/γ-Fe2O3 exhibited greatly enhanced photocatalytic activity, demonstrating that the γ-Fe2O3 played an important role in the photocatalytic process. The CdS/RGO/γ-Fe2O3 composite with PB loading amount of 12 mg exhibits the highest photocatalytic degradation efficiency of about 99.8% and the highest apparent reaction rate constant (k) value of about 0.03289 min-1, which is almost 2.9 times and 1.8 times higher than that of CdS and CdS/RGO, respectively. This result indicates that a suitable loading amount of γ-Fe2O3 is important to optimize the photocatalytic performance of the CdS/RGO/γ-Fe2O3 composites. Moreover, owing to the ferromagnetism of γ-Fe2O3, the CdS/RGO/γ-Fe2O3 photocatalyst could be easily separated from the reaction solution for recycling by a magnet. A possible photocatalytic mechanism was also proposed based on the photoluminescence (PL) characterization and the active species capture experiment. It was demonstrated that the enhanced photocatalytic degradation properties of CdS/RGO/γ-Fe2O3 composites can be ascribed to the excellent conductivity of RGO and the construction of Z-scheme heterostructure between CdS and γ-Fe2O3, which facilitate the transport and separation of photogenerated carriers.
With Prussian blue (PB) as the precursor for γ-Fe2O3, the tri-component CdS/RGO/γ-Fe2O3 photocatalyst was prepared through loading PB nanocubes and CdS nanoparticles on graphene oxide (GO) nanosheets, followed by a calcination process in inert atmosphere (N2). The content of γ-Fe2O3 in the CdS/RGO/γ-Fe2O3 photocatalyst can be adjusted by changing the loading amount of PB, and the cubic morphology of PB was maintained after the calcination. The composition, structure, morphology and light absorption of the as-prepared products were investigated by X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (FT-IR), Raman spectroscopy and ultraviolet-visible (UV-vis) spectroscopy. The photocatalytic activity of the ternary photocatalysts was evaluated by the degradation of the organic pollutant of Rhodamine B (RhB) under visible-light irradiation. It was found that the degradation process of RhB follows pseudo-first-order kinetics. Compared to the bi-component CdS/RGO photocatalyst, the tri-component CdS/RGO/γ-Fe2O3 exhibited greatly enhanced photocatalytic activity, demonstrating that the γ-Fe2O3 played an important role in the photocatalytic process. The CdS/RGO/γ-Fe2O3 composite with PB loading amount of 12 mg exhibits the highest photocatalytic degradation efficiency of about 99.8% and the highest apparent reaction rate constant (k) value of about 0.03289 min-1, which is almost 2.9 times and 1.8 times higher than that of CdS and CdS/RGO, respectively. This result indicates that a suitable loading amount of γ-Fe2O3 is important to optimize the photocatalytic performance of the CdS/RGO/γ-Fe2O3 composites. Moreover, owing to the ferromagnetism of γ-Fe2O3, the CdS/RGO/γ-Fe2O3 photocatalyst could be easily separated from the reaction solution for recycling by a magnet. A possible photocatalytic mechanism was also proposed based on the photoluminescence (PL) characterization and the active species capture experiment. It was demonstrated that the enhanced photocatalytic degradation properties of CdS/RGO/γ-Fe2O3 composites can be ascribed to the excellent conductivity of RGO and the construction of Z-scheme heterostructure between CdS and γ-Fe2O3, which facilitate the transport and separation of photogenerated carriers.
