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2018 Volume 76 Issue 2
2018, 76(2): 85-94
doi: 10.6023/A17070319
Abstract:
As the biomass energy and green chemistry processes have gained more and more attention from researchers, ionic liquids as a novel green solvent were widely concerned by research teams since 1990s, because of many excellent properties of chemical stability, low viscosity, high conductivity and so on. The research on the preparation methods and application fields is getting better, especially in the fields of catalytic reaction, photoelectron chemistry, materials chemistry and biomass pretreatment. However, some disadvantages such as large consumption, high cost, hard to separate, and complexity in purification process were appeared. Thus, in recent years, many scholars tried to immobilize ILs on inorganic porous materials or organic polymer materials by physical adsorption or chemical grafting. In this way, the characteristics of ILs were transferred to the polyphase solid catalysts, and it can be applied to the continuous and closed fixed-bed reactions. In this review, the development of immobilized ionic liquid technology were summarized in detail, and the current applications of immobilized ionic liquid were illustrated with a multi-angle. The immobilized ionic liquid as catalysts were used in chemical catalytic field depending on the chemical structure of ionic liquid; While the immobilized ionic liquid as a functional materials were used in adsorption separation field depending on the surface characteristic of solid carrier.
As the biomass energy and green chemistry processes have gained more and more attention from researchers, ionic liquids as a novel green solvent were widely concerned by research teams since 1990s, because of many excellent properties of chemical stability, low viscosity, high conductivity and so on. The research on the preparation methods and application fields is getting better, especially in the fields of catalytic reaction, photoelectron chemistry, materials chemistry and biomass pretreatment. However, some disadvantages such as large consumption, high cost, hard to separate, and complexity in purification process were appeared. Thus, in recent years, many scholars tried to immobilize ILs on inorganic porous materials or organic polymer materials by physical adsorption or chemical grafting. In this way, the characteristics of ILs were transferred to the polyphase solid catalysts, and it can be applied to the continuous and closed fixed-bed reactions. In this review, the development of immobilized ionic liquid technology were summarized in detail, and the current applications of immobilized ionic liquid were illustrated with a multi-angle. The immobilized ionic liquid as catalysts were used in chemical catalytic field depending on the chemical structure of ionic liquid; While the immobilized ionic liquid as a functional materials were used in adsorption separation field depending on the surface characteristic of solid carrier.
2018, 76(2): 95-98
doi: 10.6023/A17100473
Abstract:
Developed as novel protecting groups for solid-phase peptide synthesis, aryl boronate ester based amino acid building blocks exhibit many advantages over Alloc/Allyl groups and other traditional protecting groups due to their environmental-friendly deprotection conditions and high deprotection efficiency. These protecting groups have been found to exhibit all of the chemical properties compatible to the standard Fmoc(9-Fluorenylmethyloxycarbonyl) solid-phase peptide synthesis and to be orthogonal to other protection groups, such as tBu (tert-butyl), pbf (2, 2, 4, 6, 7-penta-methyldihydroben zofuran-5-sulfonyl), Trt (trityl) and Boc (t-Butyloxy carbonyl). In this paper, the aryl bronate ester protected Asp was employed to synthesize a lactam-bridged bicyclic peptide, BI-32169 ([Gly-Leu-Pro-Trp-Gly-Cys-Pro-Ser-Asp]-Ile-Pro-Gly-Trp-Asn-Thr-Pro-Trp-Ala-Cys), which is a human glucagon receptor peptide inhibitor, via on-resin cyclization and solution phase oxidative folding. First of all, the Fmoc-Asp(pDobb)-OH (pDobb, dihydroxyborylbenzyl pinacol ester) was successfully synthesized via esterification between Fmoc-Asp-OtBu and 4-(4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolan-2-yl) followed by deprotection of tBu with trifluoroacetic acid. Subsequently, the fully protected linear peptide was obtained by incorporating Fmoc-Asp(pDobb)-OH into peptide backbone through standard SPPS using HCTU/DIPEA as the coupling reagent and base. The following release of pDobb group on Asp side chain and deprotection of the N-terminal Fmoc group on solid support provided the linear peptide containing a free Asp residue and an N-terminal amino group. The critical cyclization step was accomplished on resin using PyAOP/HOAt/NMM, followed by resin cleavage and global deprotection with TFA/Phenol/Water/TIPS to give the monocyclic peptide. Finally, the intramolecular disulfide bond was formed through oxidative folding in an aqueous environment with 10% DMSO to provide the final bicyclic target, BI-32169, with a total yield about 27%. In summary, the human glucagon receptor peptide inhibitor BI-32169 was successfully synthesized utilizing an aryl boronate ester based amino acid building block via an on-resin cyclization and solution phase oxidative folding strategy. This convenient and efficient synthetic route could provide a way for chemical total synthesis of BI-32169 and other analogues.
Developed as novel protecting groups for solid-phase peptide synthesis, aryl boronate ester based amino acid building blocks exhibit many advantages over Alloc/Allyl groups and other traditional protecting groups due to their environmental-friendly deprotection conditions and high deprotection efficiency. These protecting groups have been found to exhibit all of the chemical properties compatible to the standard Fmoc(9-Fluorenylmethyloxycarbonyl) solid-phase peptide synthesis and to be orthogonal to other protection groups, such as tBu (tert-butyl), pbf (2, 2, 4, 6, 7-penta-methyldihydroben zofuran-5-sulfonyl), Trt (trityl) and Boc (t-Butyloxy carbonyl). In this paper, the aryl bronate ester protected Asp was employed to synthesize a lactam-bridged bicyclic peptide, BI-32169 ([Gly-Leu-Pro-Trp-Gly-Cys-Pro-Ser-Asp]-Ile-Pro-Gly-Trp-Asn-Thr-Pro-Trp-Ala-Cys), which is a human glucagon receptor peptide inhibitor, via on-resin cyclization and solution phase oxidative folding. First of all, the Fmoc-Asp(pDobb)-OH (pDobb, dihydroxyborylbenzyl pinacol ester) was successfully synthesized via esterification between Fmoc-Asp-OtBu and 4-(4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolan-2-yl) followed by deprotection of tBu with trifluoroacetic acid. Subsequently, the fully protected linear peptide was obtained by incorporating Fmoc-Asp(pDobb)-OH into peptide backbone through standard SPPS using HCTU/DIPEA as the coupling reagent and base. The following release of pDobb group on Asp side chain and deprotection of the N-terminal Fmoc group on solid support provided the linear peptide containing a free Asp residue and an N-terminal amino group. The critical cyclization step was accomplished on resin using PyAOP/HOAt/NMM, followed by resin cleavage and global deprotection with TFA/Phenol/Water/TIPS to give the monocyclic peptide. Finally, the intramolecular disulfide bond was formed through oxidative folding in an aqueous environment with 10% DMSO to provide the final bicyclic target, BI-32169, with a total yield about 27%. In summary, the human glucagon receptor peptide inhibitor BI-32169 was successfully synthesized utilizing an aryl boronate ester based amino acid building block via an on-resin cyclization and solution phase oxidative folding strategy. This convenient and efficient synthetic route could provide a way for chemical total synthesis of BI-32169 and other analogues.
2018, 76(2): 99-102
doi: 10.6023/A17110519
Abstract:
Decarboxylation reactions have been widely explored in recent ten years, and decarboxylative cascade reaction of cinnamic acids has also attracted much attention. Generally, this class of reaction includes two processes:radical addition and decarboxylation. The result of reaction can introduce kinds of functional groups on the benzene ring, such as halogen atom, nitro-group and trifluoromethyl. Following the continuous studies of our group on oxidative cascade reaction, especially the oxidative reaction in the absence of metal, herein we disclosed a decarboxylative oxidative cascade reaction of cinnamic acids under metal-free conditions. We employed K2CO3 as base, tert-butyl hydroperoxide (TBHP) as oxidant and DMSO/H2O as co-solvent, and cinnamic acids could be converted to propiophenone derivatives in moderate yield. To get an insight into the mechanism of this process, several controlled experiments were conducted. First, DMSO-d6 was employed under the standard conditions and no d-methyl was detected in the 1H NMR spectrum of product. It demonstrated that the methyl of product was derived from tert-butyl hydroperoxide. Subsequently, the reaction was carried out under nitrogen and oxygen atmosphere, and it was found that higher reaction efficiency was obtained in N2. The result indicated that methyl radical was easily quenched by oxygen. On the basis of experiment results, we proposed a plausible mechanism. First, tert-butyl hydroperoxide yielded methyl radical, then the reaction underwent radical addition and decarboxylation to generate the desired product. The reaction featured that tert-butyl hydroperoxide was used as oxidant and methylation reagent in this process, and the reaction proceeded under metal-free and aqueous phase condition. Therefore, it met the requirement of green chemistry. Meanwhile, the operation of reaction was also simple, for example, to a DMSO/H2O (0.5 mL/0.5 mL) solution of cinnamic acids (0.2 mmol) were successively added K2CO3 (0.3 mmol), TBHP (0.8 mmol). The reaction mixture was stirred at 100 ℃. Upon the completion, the desired product was purified by silica gel column chromatography.
Decarboxylation reactions have been widely explored in recent ten years, and decarboxylative cascade reaction of cinnamic acids has also attracted much attention. Generally, this class of reaction includes two processes:radical addition and decarboxylation. The result of reaction can introduce kinds of functional groups on the benzene ring, such as halogen atom, nitro-group and trifluoromethyl. Following the continuous studies of our group on oxidative cascade reaction, especially the oxidative reaction in the absence of metal, herein we disclosed a decarboxylative oxidative cascade reaction of cinnamic acids under metal-free conditions. We employed K2CO3 as base, tert-butyl hydroperoxide (TBHP) as oxidant and DMSO/H2O as co-solvent, and cinnamic acids could be converted to propiophenone derivatives in moderate yield. To get an insight into the mechanism of this process, several controlled experiments were conducted. First, DMSO-d6 was employed under the standard conditions and no d-methyl was detected in the 1H NMR spectrum of product. It demonstrated that the methyl of product was derived from tert-butyl hydroperoxide. Subsequently, the reaction was carried out under nitrogen and oxygen atmosphere, and it was found that higher reaction efficiency was obtained in N2. The result indicated that methyl radical was easily quenched by oxygen. On the basis of experiment results, we proposed a plausible mechanism. First, tert-butyl hydroperoxide yielded methyl radical, then the reaction underwent radical addition and decarboxylation to generate the desired product. The reaction featured that tert-butyl hydroperoxide was used as oxidant and methylation reagent in this process, and the reaction proceeded under metal-free and aqueous phase condition. Therefore, it met the requirement of green chemistry. Meanwhile, the operation of reaction was also simple, for example, to a DMSO/H2O (0.5 mL/0.5 mL) solution of cinnamic acids (0.2 mmol) were successively added K2CO3 (0.3 mmol), TBHP (0.8 mmol). The reaction mixture was stirred at 100 ℃. Upon the completion, the desired product was purified by silica gel column chromatography.
2018, 76(2): 103-106
doi: 10.6023/A17110476
Abstract:
1, 2, 3, 4-Tetrahydropyrrolo[1, 2-a]pyrazines are an important motif due to their biological activities and widely existing in natural products. Notably, the substituent and the absolute configuration are important for the medicinal efficacy. Thus, the synthesis of chiral tetrahydropyrrolo[1, 2-a]pyrazines has attracted much attention of scientists. Most synthetic methods utilized chiral starting materials or auxiliaries. Kinetic resolution was an alternative way to give chiral tetrahydropyrrolo[1, 2-a]pyrazines. The first cata-lytic asymmetric synthetic method was developed in 2011 by Li and Antilla through a chiral phosphoric acid-catalyzed asymmetric intramolecular aza-Friedel-Crafts reaction of aldehydes with N-aminoethylpyrroles in high enantiocontrol level. Subsequently, the sequential aerobic oxidation-asymmetric intramolecular aza-Friedel-Crafts reaction between N-aminoethylpyrroles and benzyl alcohols for the synthesis of tetrahydropyrrolo[1, 2-a]pyrazines was realized using chiral bifunctional heterogeneous materials composed of Au/Pd nanoparticles and chiral phosphoric acids. The asymmetric hydrogenation as an efficient way has been successfully applied to synthesize the kind of chiral amines. In 2012, Our group achieved the asymmetric hydrogenation of 1-substituted pyrrolo[1, 2-a]pyrazines via a substrate activation strategy. Recently, we reported the direct asymmetric hydrogenation of 3-substituted pyrrolo[1, 2-a]pyrazines in up to 96% ee values. Considering their impressive significance, herein, we successfully hydrogenated 3, 4-dihydropyrrolo[1, 2-a]pyrazines and 3, 4-dihydroindolo[1, 2-a]pyrazines with up to 99% yield and 95% ee. The reaction features mild condition, high enantioselectivity and high atom-economy. The typical procedure for asymmetric hydrogenation is as follows:A mixture of[Ir(COD)Cl]2 (3.0 mg, 0.0045 mmol) and the ligand Cy-WalPhos (6.6 mg, 0.0099 mmol) was stirred in toluene (1.0 mL) at room temperature for 5 min in the glove box. Then the solution was transferred to the vial containing the substrate 3, 4-dihydropyrrolo[1, 2-a]pyrazines (0.3 mmol) together with toluene (2.0 mL). The vial was taken to an autoclave and the hydrogenation was conducted at 40℃ as well as at a hydrogen pressure of 500 psi for 48 h. After carefully releasing the hydrogen, the autoclave was opened and the toluene was evaporated in vacuo. The residue was purified by column chromatography to afford the corresponding chiral tetrahydropyrrolo[1, 2-a]pyrazines.
1, 2, 3, 4-Tetrahydropyrrolo[1, 2-a]pyrazines are an important motif due to their biological activities and widely existing in natural products. Notably, the substituent and the absolute configuration are important for the medicinal efficacy. Thus, the synthesis of chiral tetrahydropyrrolo[1, 2-a]pyrazines has attracted much attention of scientists. Most synthetic methods utilized chiral starting materials or auxiliaries. Kinetic resolution was an alternative way to give chiral tetrahydropyrrolo[1, 2-a]pyrazines. The first cata-lytic asymmetric synthetic method was developed in 2011 by Li and Antilla through a chiral phosphoric acid-catalyzed asymmetric intramolecular aza-Friedel-Crafts reaction of aldehydes with N-aminoethylpyrroles in high enantiocontrol level. Subsequently, the sequential aerobic oxidation-asymmetric intramolecular aza-Friedel-Crafts reaction between N-aminoethylpyrroles and benzyl alcohols for the synthesis of tetrahydropyrrolo[1, 2-a]pyrazines was realized using chiral bifunctional heterogeneous materials composed of Au/Pd nanoparticles and chiral phosphoric acids. The asymmetric hydrogenation as an efficient way has been successfully applied to synthesize the kind of chiral amines. In 2012, Our group achieved the asymmetric hydrogenation of 1-substituted pyrrolo[1, 2-a]pyrazines via a substrate activation strategy. Recently, we reported the direct asymmetric hydrogenation of 3-substituted pyrrolo[1, 2-a]pyrazines in up to 96% ee values. Considering their impressive significance, herein, we successfully hydrogenated 3, 4-dihydropyrrolo[1, 2-a]pyrazines and 3, 4-dihydroindolo[1, 2-a]pyrazines with up to 99% yield and 95% ee. The reaction features mild condition, high enantioselectivity and high atom-economy. The typical procedure for asymmetric hydrogenation is as follows:A mixture of[Ir(COD)Cl]2 (3.0 mg, 0.0045 mmol) and the ligand Cy-WalPhos (6.6 mg, 0.0099 mmol) was stirred in toluene (1.0 mL) at room temperature for 5 min in the glove box. Then the solution was transferred to the vial containing the substrate 3, 4-dihydropyrrolo[1, 2-a]pyrazines (0.3 mmol) together with toluene (2.0 mL). The vial was taken to an autoclave and the hydrogenation was conducted at 40℃ as well as at a hydrogen pressure of 500 psi for 48 h. After carefully releasing the hydrogen, the autoclave was opened and the toluene was evaporated in vacuo. The residue was purified by column chromatography to afford the corresponding chiral tetrahydropyrrolo[1, 2-a]pyrazines.
2018, 76(2): 107-112
doi: 10.6023/A17090422
Abstract:
Self N-doped porous cross-linked carbon nanosheets (N-ICNs) are prepared by one-step activation carbonization using dandelion seeds. The dandelion seeds are rich in nitrogen without any additional doping treatment, which can be served as an ideal carbon precursor. The microstructure and composition of the prepared carbon materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It can be seen from the SEM and TEM spectra that the N-ICNs exhibit the porous interconnected structure, which can facilitate the transfer of the electrons and the dispersion of the electrolyte ions. Moreover, the XRD spectra show the defects in the amorphous carbon material. Nitrogen adsorption/desorption isotherms of the N-ICNs show a high specific surface area of 1564 m2·g-1, and the pore size distribution shows numerous micropores and macropores, which contributes to the formation of double layer capacitance and the accessibility of the electrolyte ions. The wide-scan spectra present the presence of C, N and O atoms. Interestingly, the N content of the N-ICNs without any extra doping treatment is high (2.88%). Based on the high nitrogen content, the N-ICNs exhibit a good specific capacitance of 337 F·g-1 at a current density of 1 A·g-1 with an excellent capacitance retention of 99% after 10000 cycles. The good electrochemical performances mainly caused by the nitrogen functional groups in the carbon lattice, which can improve the wettability as well as provide pseudocapacitance due to the redox reactions of amine groups. In addition, the symmetric supercapacitor assembled with N-ICNs in the operating voltage range of 0~2 V shows high energy density of 25.3 Wh·kg-1 at the power density of 900 W·kg-1, which are superior than the other carbon materials reported. And the capacitance retention can retain 98% after 10000 cycles. Therefore, the low-cost biomass-derived porous interconnected carbon material can be a promising electrode material for supercapacitors.
Self N-doped porous cross-linked carbon nanosheets (N-ICNs) are prepared by one-step activation carbonization using dandelion seeds. The dandelion seeds are rich in nitrogen without any additional doping treatment, which can be served as an ideal carbon precursor. The microstructure and composition of the prepared carbon materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It can be seen from the SEM and TEM spectra that the N-ICNs exhibit the porous interconnected structure, which can facilitate the transfer of the electrons and the dispersion of the electrolyte ions. Moreover, the XRD spectra show the defects in the amorphous carbon material. Nitrogen adsorption/desorption isotherms of the N-ICNs show a high specific surface area of 1564 m2·g-1, and the pore size distribution shows numerous micropores and macropores, which contributes to the formation of double layer capacitance and the accessibility of the electrolyte ions. The wide-scan spectra present the presence of C, N and O atoms. Interestingly, the N content of the N-ICNs without any extra doping treatment is high (2.88%). Based on the high nitrogen content, the N-ICNs exhibit a good specific capacitance of 337 F·g-1 at a current density of 1 A·g-1 with an excellent capacitance retention of 99% after 10000 cycles. The good electrochemical performances mainly caused by the nitrogen functional groups in the carbon lattice, which can improve the wettability as well as provide pseudocapacitance due to the redox reactions of amine groups. In addition, the symmetric supercapacitor assembled with N-ICNs in the operating voltage range of 0~2 V shows high energy density of 25.3 Wh·kg-1 at the power density of 900 W·kg-1, which are superior than the other carbon materials reported. And the capacitance retention can retain 98% after 10000 cycles. Therefore, the low-cost biomass-derived porous interconnected carbon material can be a promising electrode material for supercapacitors.
2018, 76(2): 113-120
doi: 10.6023/A17070328
Abstract:
The hydrosilylative reduction with silane is a popular defunctionalization strategy to convert biomass into chemicals and energies because of the mild reaction conditions. Among these, the reduction of C-O bond is particularly important because of its application in sugar biomass reduction. The (C6F5)3 B/silane catalytic system has been frequently used in the reduction of C-O bonds in the past years. However, Brookhart et al. reported alkyl ethers reduction by using Ir(Ⅲ) pincer catalyst and reductant HSiEt3. This work provides a novel hydrosilylation catalyst for C-O reduction and an effective method for sugar biomass deoxygenation. According to the previous mechanistic proposals on similar Ir catalysed hydrosilylation reactions, the iridium dihydride complex, iridium silyl hydride complex, silane adduct iridium complex and iridium silyl trihydride complex might possibly act as the hydride source. We carried out the theoretical study on Brookhart's Ir(Ⅲ) Pincer Complex/HSiEt3 catalyzed hydrosilylation reaction of EtOEt yielding ethane and EtOSiEt3. The density functional theory (DFT) calculations in our study indicate that the iridium dihydride complex is the best hydride source. Our calculation result is consistent well with experimental observations in Brookhart's experiment. For example, the phenomenon that adding iridium dihydride complex into the reaction system increases the reaction rate is understandable because the complex is involved in the rate-determining step. From the Distortion/Interaction analysis, we found that hydride transfer steps on the other three possible hydride sources are disfavoured by the HSiEt3/-SiEt3 group (derived from HSiEt3) bonded with Ir center. The iridium silyl hydride complex is unfavourable because the Ir-H bond is strengthened and the pincer ligand is distorted. For the silane adduct iridium complex, the coordination of HSiEt3 destabilizes iridium complex intermediate for entropy increases and trans effect, and destabilizes the related transition state by damaging its pincer ligand. Further, the corresponding hydride transfer transition state from iridium silyl trihydride is highly unstable and Si-H bond always reform automatically. What's more important, the moderate bond dissociation energy of Ir-hydride, small steric hindrance and the promotion effect of SiEt3 group coordination with ether all facilitate the hydride transfer on the iridium dihydride complex.
The hydrosilylative reduction with silane is a popular defunctionalization strategy to convert biomass into chemicals and energies because of the mild reaction conditions. Among these, the reduction of C-O bond is particularly important because of its application in sugar biomass reduction. The (C6F5)3 B/silane catalytic system has been frequently used in the reduction of C-O bonds in the past years. However, Brookhart et al. reported alkyl ethers reduction by using Ir(Ⅲ) pincer catalyst and reductant HSiEt3. This work provides a novel hydrosilylation catalyst for C-O reduction and an effective method for sugar biomass deoxygenation. According to the previous mechanistic proposals on similar Ir catalysed hydrosilylation reactions, the iridium dihydride complex, iridium silyl hydride complex, silane adduct iridium complex and iridium silyl trihydride complex might possibly act as the hydride source. We carried out the theoretical study on Brookhart's Ir(Ⅲ) Pincer Complex/HSiEt3 catalyzed hydrosilylation reaction of EtOEt yielding ethane and EtOSiEt3. The density functional theory (DFT) calculations in our study indicate that the iridium dihydride complex is the best hydride source. Our calculation result is consistent well with experimental observations in Brookhart's experiment. For example, the phenomenon that adding iridium dihydride complex into the reaction system increases the reaction rate is understandable because the complex is involved in the rate-determining step. From the Distortion/Interaction analysis, we found that hydride transfer steps on the other three possible hydride sources are disfavoured by the HSiEt3/-SiEt3 group (derived from HSiEt3) bonded with Ir center. The iridium silyl hydride complex is unfavourable because the Ir-H bond is strengthened and the pincer ligand is distorted. For the silane adduct iridium complex, the coordination of HSiEt3 destabilizes iridium complex intermediate for entropy increases and trans effect, and destabilizes the related transition state by damaging its pincer ligand. Further, the corresponding hydride transfer transition state from iridium silyl trihydride is highly unstable and Si-H bond always reform automatically. What's more important, the moderate bond dissociation energy of Ir-hydride, small steric hindrance and the promotion effect of SiEt3 group coordination with ether all facilitate the hydride transfer on the iridium dihydride complex.
2018, 76(2): 121-132
doi: 10.6023/A17090442
Abstract:
Magnesium silylamido complexes 1~7 bearing non-symmetric β-diketiminate ligands were synthesized via the reactions of corresponding proligands HL1~7 with one equivalent of Mg[N(SiMe3)2]2 at 80℃ in toluene. All complexes were characterized by 1H NMR, 13C NMR and elemental analysis. The monomeric nature of complexes 1 and 5 in the solid state was further confirmed by X-ray diffraction studies. In both complexes, the metal center is tri-coordinated by the β-diketiminate ligand and one silylamido group. The very close bond lengths of two Mg-N bonds as well as close C-N distances of the chelate ring indicate significant delocalization. The apparent deviation of the magnesium center from the ligand backbone plane suggests a certain ηn-coordination nature of the ligand to the metal center. These magnesium silylamido complexes showed good catalytic activities for the ring-opening polymerization of rac-lactide under ambient conditions, and could polymerize 300 equivalents of rac-lactide to high molecular weight polymers within short time in THF. The solvent effect played a critical role during the polymerization process. All complexes showed higher catalytic activity in THF than in toluene. Taking complex 2 as an example, a monomer conversion of 96% could be achieved within 10 min in THF, whereas a conversion of 80% could only be achieved within extended polymerization time of 210 min in toluene (Table 1 , Entries 6 and 9, [LA]0/[Mg]0=100). Upon the addition of isopropanol, the activities of magnesium silylamido complexes 1~7 increased significantly. For instance, when the polymerization runs were carried in THF in the presence of isopropanol, the reaction time could be reduced to 10~20 min even with a high molar ratio of[LA]0/[Mg]0=300. Moreover, the type and location of the substituent(s) on the N-aryl group of the β-diketiminate ligand exerts a significant influence on the catalytic activity of the corresponding complex toward the polymerization of rac-lactide. In the absence of excess isopropanol, the introduction of sterically demanding substituent to the ortho-position of N-aryl ring leads to a decrease of the polymerization activity; but the influence of electron-withdrawing group is different in different solvents (toluene or THF). These magnesium complexes could produce heterotactic polymers in THF (Pr=0.64~0.80) and atactic polymers in toluene (Pr=0.45~0.58). Magnesium complexes 1~7 also displayed high catalytic activities for the ring-opening polymerization (ROP) of ε-caprolactone, among them complexes bearing β-diketiminate ligand with bulky ortho-substituted N-aryl rings showed higher activities. Generally, the ROPs of ε-caprolactone initiated by these magnesium silylamido complexes were not well-controlled, giving moderately distributed polymers (Mw/Mn=1.37~1.67). Additionally, diblock copolymers of L-lactide and ε-caprolactone were obtained by using 2 as the initiator via both sequential feeding of two monomers (in either order) and the one-pot method. The formation of diblock copolymers were verified by 1H NMR, 13C NMR, DSC and GPC analysis.
Magnesium silylamido complexes 1~7 bearing non-symmetric β-diketiminate ligands were synthesized via the reactions of corresponding proligands HL1~7 with one equivalent of Mg[N(SiMe3)2]2 at 80℃ in toluene. All complexes were characterized by 1H NMR, 13C NMR and elemental analysis. The monomeric nature of complexes 1 and 5 in the solid state was further confirmed by X-ray diffraction studies. In both complexes, the metal center is tri-coordinated by the β-diketiminate ligand and one silylamido group. The very close bond lengths of two Mg-N bonds as well as close C-N distances of the chelate ring indicate significant delocalization. The apparent deviation of the magnesium center from the ligand backbone plane suggests a certain ηn-coordination nature of the ligand to the metal center. These magnesium silylamido complexes showed good catalytic activities for the ring-opening polymerization of rac-lactide under ambient conditions, and could polymerize 300 equivalents of rac-lactide to high molecular weight polymers within short time in THF. The solvent effect played a critical role during the polymerization process. All complexes showed higher catalytic activity in THF than in toluene. Taking complex 2 as an example, a monomer conversion of 96% could be achieved within 10 min in THF, whereas a conversion of 80% could only be achieved within extended polymerization time of 210 min in toluene (
2018, 76(2): 133-137
doi: 10.6023/A17090418
Abstract:
Cryptomelane-type manganese dioxide (OMS-2) is a very important nanomaterial in electrochemistry. Its intrinsic properties can be tailored by controlling shape or size. The diameter of one-dimensional OMS-2 nanomaterial is an important parameter in controllable synthesis and electrochemistry applications. Generally, the control of the diameter of one-dimensional OMS-2 nanomaterial can be realized by cosolvents or surfactants, even other special methods. In this paper, without any acid added, a series of one-dimensional OMS-2 nanomaterial with different diameters were synthesized by adjusting the ratio of potassium permanganate to manganese sulfate monohydrate in the aqueous solution with the conditional reflux method. The typical samples were characterized in detail by N2 adsorption-desorption analyses (BET), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscope (TEM) and hydrogen temperature-programmed reduction (H2-TPR). The results reconfirmed that the growth of OMS-2 nanofibers and nanowires mainly followed the lateral attachment mechanism. The role of Oswald ripening in the growth of one-dimensional OMS-2 nanomaterials was making two or more primary thinner nanofibers or nanowires welded together. In the synthesis process, all the conditions were strictly controlled. The samples synthesized at low ratio of MnO4- to Mn2+ showed thinner and longer nanofibers or nanowires, and the samples synthesized at high ratio of MnO4- to Mn2+ exhibited higher diameter. Therefore, it can be concluded that MnO4- can promote the lateral growth of one-dimensional OMS-2 nanomaterials and Mn2+ tends to promote the longitudinal growth. In the electrochemical tests, when the ratio of potassium permanganate to manganese sulfate monohydrate increased from 0.15 to 1.80, the specific capacitance of one-dimensional OSM-2 nanomaterials decreased gradually. Therefore, the specific capacitance of one-dimensional OSM-2 nanomaterial was directly related to their diameters. The smaller the diameter is, the larger the capacitance is. The specific capacitance of MnO-15, MnO-45, MnO-112 and MnO-180 was 375, 230, 144 and 77 F/g, respectively. The result of galvanostatic charge and discharge of four samples at the current density of 1 A/g in 1 mol/L Na2SO4 solution was consistent with the cyclic voltammetry.
Cryptomelane-type manganese dioxide (OMS-2) is a very important nanomaterial in electrochemistry. Its intrinsic properties can be tailored by controlling shape or size. The diameter of one-dimensional OMS-2 nanomaterial is an important parameter in controllable synthesis and electrochemistry applications. Generally, the control of the diameter of one-dimensional OMS-2 nanomaterial can be realized by cosolvents or surfactants, even other special methods. In this paper, without any acid added, a series of one-dimensional OMS-2 nanomaterial with different diameters were synthesized by adjusting the ratio of potassium permanganate to manganese sulfate monohydrate in the aqueous solution with the conditional reflux method. The typical samples were characterized in detail by N2 adsorption-desorption analyses (BET), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscope (TEM) and hydrogen temperature-programmed reduction (H2-TPR). The results reconfirmed that the growth of OMS-2 nanofibers and nanowires mainly followed the lateral attachment mechanism. The role of Oswald ripening in the growth of one-dimensional OMS-2 nanomaterials was making two or more primary thinner nanofibers or nanowires welded together. In the synthesis process, all the conditions were strictly controlled. The samples synthesized at low ratio of MnO4- to Mn2+ showed thinner and longer nanofibers or nanowires, and the samples synthesized at high ratio of MnO4- to Mn2+ exhibited higher diameter. Therefore, it can be concluded that MnO4- can promote the lateral growth of one-dimensional OMS-2 nanomaterials and Mn2+ tends to promote the longitudinal growth. In the electrochemical tests, when the ratio of potassium permanganate to manganese sulfate monohydrate increased from 0.15 to 1.80, the specific capacitance of one-dimensional OSM-2 nanomaterials decreased gradually. Therefore, the specific capacitance of one-dimensional OSM-2 nanomaterial was directly related to their diameters. The smaller the diameter is, the larger the capacitance is. The specific capacitance of MnO-15, MnO-45, MnO-112 and MnO-180 was 375, 230, 144 and 77 F/g, respectively. The result of galvanostatic charge and discharge of four samples at the current density of 1 A/g in 1 mol/L Na2SO4 solution was consistent with the cyclic voltammetry.
2018, 76(2): 138-142
doi: 10.6023/A17070347
Abstract:
The spectra of the van der Waals (vdW) complexes provide useful information on the intermolecular potential energy surfaces (PESs) and dynamics of such weakly bound molecules. First and foremost, an accurate potential energy surface is required to allow for spectroscopic analysis for van der Waals complexes. Thus, constructing an effective reduced-dimension potential energy surface, which includes direct relevant intramolecular modes, is the most feasible way and widely used in the recent potential studies. In this work, we present a four-dimensional (4D) ab initio potential energy surface (PES) of the Kr-CS2 complex at the coupled-cluster singles and doubles with noniterative inclusion of connected triples[CCSD(T)]-F12 level. We employed the aug-cc-pVTZ basis set of Woon and Dunning for the C and S atoms and the aug-cc-pVTZ-PP basis set for Kr. The bond functions (3s3p2d1f1g) (for 3s and 3p, α=0.9, 0.3, 0.1; for 2d, α=0.6, 0.2; for f and g, α=0.3) were placed at the mid-point of the R vector. The Q1 and Q3 normal modes for the ν1 symmetric stretching vibration and ν3 antisymmetric stretching vibration of CS2 were explicitly taken into account in the calculations of the Kr-CS2 potential energies. Two vibrationally averaged potentials with CS2 at both the vibrational ground and the ν1+ν3 excited states were generated from the integration of the four-dimensional potential over the Q1 and Q3 coordinates. Each potential contains a T-shaped global minimum and two equivalent linear local minima. These fits to 9000 points have root-mean-square (rms) deviations of 0.143 and 0.145 cm-1 for the ground and the ν1+ν3 excited states, respectively. The radial discrete variable representation (DVR)/angular finite basis representation (FBR) method and Lanczos algorithm were employed to calculate the rovibrational states without separating the inter-and intra-molecular vibrations. The spectroscopic parameters for the ground and the ν1+ν3 excited states of Kr-CS2 are predicted. In addition, the predicted band origin shift is -1.2357 cm-1 for Kr-CS2.
The spectra of the van der Waals (vdW) complexes provide useful information on the intermolecular potential energy surfaces (PESs) and dynamics of such weakly bound molecules. First and foremost, an accurate potential energy surface is required to allow for spectroscopic analysis for van der Waals complexes. Thus, constructing an effective reduced-dimension potential energy surface, which includes direct relevant intramolecular modes, is the most feasible way and widely used in the recent potential studies. In this work, we present a four-dimensional (4D) ab initio potential energy surface (PES) of the Kr-CS2 complex at the coupled-cluster singles and doubles with noniterative inclusion of connected triples[CCSD(T)]-F12 level. We employed the aug-cc-pVTZ basis set of Woon and Dunning for the C and S atoms and the aug-cc-pVTZ-PP basis set for Kr. The bond functions (3s3p2d1f1g) (for 3s and 3p, α=0.9, 0.3, 0.1; for 2d, α=0.6, 0.2; for f and g, α=0.3) were placed at the mid-point of the R vector. The Q1 and Q3 normal modes for the ν1 symmetric stretching vibration and ν3 antisymmetric stretching vibration of CS2 were explicitly taken into account in the calculations of the Kr-CS2 potential energies. Two vibrationally averaged potentials with CS2 at both the vibrational ground and the ν1+ν3 excited states were generated from the integration of the four-dimensional potential over the Q1 and Q3 coordinates. Each potential contains a T-shaped global minimum and two equivalent linear local minima. These fits to 9000 points have root-mean-square (rms) deviations of 0.143 and 0.145 cm-1 for the ground and the ν1+ν3 excited states, respectively. The radial discrete variable representation (DVR)/angular finite basis representation (FBR) method and Lanczos algorithm were employed to calculate the rovibrational states without separating the inter-and intra-molecular vibrations. The spectroscopic parameters for the ground and the ν1+ν3 excited states of Kr-CS2 are predicted. In addition, the predicted band origin shift is -1.2357 cm-1 for Kr-CS2.
