生物质平台化合物电催化制备高值燃料与化学品研究进展

生物质是一类丰富的可再生碳基资源,有望代替传统化石资源生产燃料和化学品,受到了广泛关注和研究.近年来,电催化作为一种绿色高效的转化策略,成为生物质催化转化的重要研究方向之一,具有巨大的应用前景.本文总结了生物质平台化合物电催化制备高附加值燃料与化学品的研究进展,根据反应类型重点介绍了电催化氧化、还原和偶联反应,对催化反应过程和机理进行了阐述,并对电催化生物炼制的前景进行了展望.     

Recyclable ligand-free mesoporous heterogeneous Pd catalysts for Heck coupling

Ligand-free Pd-MCM41 catalysts are highly active in the Heck coupling of bromoarenes including deactivated bromo derivatives to give coupled products in high yields with high selectivities without the need to exclude air or moisture. The catalyst samples exhibit unprecedented stability among heterogeneous catalysts and can be reused at least 20 times to achieve complete conversion without any additional activation treatment.     

Chromium(II)-catalyzed diastereoselective pinacol type cross coupling: studies of substrate-controlled effects

Using 20 mol % of CrCl₂ as catalyst, manganese powder as reducing agent, and TMS-Cl as scavenger, various acroleins and aldehydes were coupled with moderate to high yields and diastereomeric excesses. Alkyl aldehydes usually favor syn configuration while aldehydes with functional groups containing chelating hetero atoms promote the formation of anti configuration. Using sterically demanding alkyl residues on the acrolein substrate, the syn configuration is definitely preferred.     

铁基费托合成催化剂相变调控及反应性能

在Fe基模型催化剂上,通过先深度还原后控制碳化的方法实现了物相结构的调控.采用X射线衍射、穆斯堡尔谱、程序升温脱附技术和激光拉曼光谱等方法表征了催化剂还原和反应前后的物化性质,并在固定床反应器中考察了不同条件活化后催化剂上费托反应性能.结果表明,H₂还原后的催化剂主要由α-Fe相组成,且随着还原温度的提高,α-Fe相的致密程度增加,平均晶粒尺寸增加,稳定性提高;再采用乙烯对H₂还原后催化剂进行碳化,可有效控制α-Fe的碳化速度,使碳化过程主要发生在Fe晶粒表层,同时改变了催化剂在反应过程中的物相变化,乃至其催化性能.与纯H₂或合成气气氛活化的催化剂相比,采用先H₂还原后乙烯碳化的预处理方法能够明显提高催化剂的活性和稳定性.     

The destruction of organic pollutants under mild reaction conditions: A review

A survey of the literature covering the destruction of organic pollutants accomplished under mild reaction conditions is presented. Technologies presented are segregated according to two main reaction pathways; oxidation and reduction. Sub-topics discussed are representative of the main component of the degradation system, including the following; electrochemical reactors, hydrogen as a reducing agent, zero-valent metals, biological based systems, photolytic processes, Fenton reaction, and a recently discovered process that is a form of room temperature and pressure oxygen activation.     

Palladium(II) complexes containing a bulky pyridinyl N-heterocyclic carbene ligand: Preparation and reactivity

Coordination chemistry of a pyridine imidazole-2-ylidene ligand (pyN ˆC) with sterically hindered substituents toward palladium(II) metal ions has been investigated. The palladium carbene complex [(C-pyN ˆC)Pd(η³-allyl)Cl] (3) is prepared via the transmetallation from the corresponding silver carbene complexes with [ClPd(η³-allyl)]₂. Upon the abstraction of chloride, coordination of pyridinyl-nitrogen becomes feasible to form [C,N-(pyN ˆC)Pd(η³-allyl)](BF₄) (4). Ligand substitution reaction of 4 with triphenylphosphine results in the formation of [(C-pyN ˆC)Pd(PPh₃)(η³-allyl)](BF₄)], which the pyridinyl-nitrogen donor is substituted by the phosphine. This palladium complex appears to be base sensitive. Treatment of 4 with t-butoxide causes the decomposition to yield the metal nano-particles. Furthermore, de-complexation of 4 takes place under hydrogen atmosphere to generate the carbene precursor, 1-(6-mesityl-2-picolyl)-3-mesitylimidazolium salt. Nevertheless, the palladium complex 4 shows good catalytic activity on the Suzuki-Miyaura and Mizoroki-Heck reactions.     

Stereoselective synthesis of the C14C23 fragment of biselyngbyolide A and B enabled by transition metal catalysis

Transition metal catalysis has enabled the highly stereoselective and protecting group-free synthesis of the C14C23 fragment of the apoptosis-inducing natural products biselyngbyolide A and B. A Pd-catalyzed Stille reaction between a vinyl stannane and a crotyl carbonate formed the skipped diene with complete control of the trisubstituted bond and excellent control over the branched/linear products. A Cu-catalyzed Stahl oxidation was used to form the requisite aldehyde needed for a Ag-catalyzed asymmetric allylation. The latter provided the final fragment with excellent stereochemical control.     

Synthesis of symmetrical 1, 3-diynes via tandem reaction of (Z)-arylvinyl bromides in the presence of DBU and CuI

Microwave-assisted tandem reaction of(Z)-arylvinyl bromides involving an elimination and homocoupling in the presence of DBU and Cul in DMF affords a variety of symmetrical 1,3-diynes in good to excellent yields.This tandem process,eliminating the need of volatile and savory terminal alkynes,provides an alternative to the conventional homocoupling methods for the synthesis of symmetrical 1,3-diynes.     

壳聚糖接枝共聚改性最新研究进展

壳聚糖是一种天然高分子,也是迄今为止唯一发现的阳离子碱性多糖。壳聚糖分子链中富含羟基和氨基等反应性官能团,具有生物相容性、生物可降解性、抗菌性、无细胞毒性等优良性能,在生化、医药、环保、农业等领域有广泛的应用前景。然而,由于其大分子具有较好的立构规整性和较强的氢键作用,除稀盐酸、稀醋酸外,壳聚糖不溶于水和其它有机溶剂,因而限制了它的应用范围。为了扩大其应用领域,常通过接枝共聚反应来改善壳聚糖的性能。本文介绍了壳聚糖接枝共聚改性的最新研究进展,包括自由基引发接枝法、偶联接枝法以及催化接枝法。     

Reactivity of TEMPO anion as a nucleophile and its applications for selective transformations of haloalkanes or acyl halides to aldehydes

Sodium 2,2,6,6-tetramethylpiperidine-N-oxide (TEMPO⁻Na⁺), generated by reduction of TEMPO· with sodium naphthalenide in THF, reacted with alkyl halides or acyl halides to produce O-alkylated or acylated TEMPOs, which were in turn oxidized with mCPBA or reduced with DIBAL-H to afford the corresponding aldehydes, thus accomplishing a new protocol for the halides-carbonyls conversion.     

A simple and convenient method for the preparation of diborane from tetrabutylammonium borohydride and benzyl chloride for application in organic synthesis

Diborane is readily generated in situ at 25 °C in toluene using the Bu₄NBH₄/PhCH₂Cl and Bu₄NBH₄/I₂ reagent systems. The reagent prepared in this way is used for the reduction of carbonyl compounds and hydroboration-oxidation of olefins to obtain the corresponding alcohols in good yields.     

An evaluation of phosphine and carbene adducts of phosphite- and phosphinite-based palladacycles in the coupling of alkyl bromides with aryl boronic acids

A range of palladacyclic catalysts and their phosphine and carbene adducts were tested in the Suzuki coupling of an alkyl bromide with phenylboronic acid and showed modest activity in some cases. Unlike with aryl halide substrates it appears that there is no particular benefit in the use of palladacycles as the palladium source. Initial data indicate that the rate determining step is not the oxidative addition of the alkyl halide substrate, but rather lies later in the catalytic cycle.     

Platinum carbonyl derived catalysts on inorganic and organic supports: a comparative study

Fumed silica, silica gel, silica-alumina and cross-linked (5.5%) polystyrene have been functionalized with quaternary ammonium groups and the Chini cluster [Pt₁₂(CO)₂₄]²⁻ has been anchored onto these functionalized materials by ion pairing. A catalyst has also been prepared by the adsorption of Na₂[Pt₁₂(CO)₂₄] on unfunctionalized fumed silica. The catalytic activities of the resultant materials, and that of commercially purchased 5% platinum on alumina have been studied for the hydrogenation of a variety of unsaturated compounds. The substrates studied are: α-acetamidocinnamic acid, cyclohexanone, acetophenone, methyl pyruvate, ethyl acetoacetate, nitrobenzene and benzonitrile. Compared to the polystyrene supported catalyst, the inorganic oxide supported catalysts have higher surface areas and for most of the substrates have notably higher activities. The functionalized fumed silica-based catalyst gives higher conversions than functionalized silica gel and silica-alumina-based catalysts. In the hydrogenation of acetophenone and ethyl acetoacetate, the functionalized fumed silica-based catalyst show superior activity compared to the commercial platinum catalyst, and the catalyst made by conventional adsorption method. In benzonitrile hydrogenation with all the cluster-derived catalysts a hydrazine derivative is selectively formed, but when the commercial platinum catalyst is used benzyl amine is the main product.     

Direct formation of silver nanoparticles in cuttlebone-derived organic matrix for catalytic applications

Development of biologically derived materials for the construction of materials with new functions is a crucial intersection of materials science and biotechnology, which is currently a topic of research interest. In this paper, we report on the use of cuttlebone-derived organic matrix (CDOM) as scaffold and reducer for the formation of silver nanoparticles (AgNPs). The experiment was carried out by simple immersing of CDOM in tollen’s reagent and incubating at 80 °C. UV–vis spectra and TEM were utilized to characterize the AgNPs and investigate their formation process. Results demonstrate that the size and distribution of AgNPs are influenced by the incubation time and protein component in CDOM. Furthermore, the AgNPs–CDOM composite was applied to catalyze the reduction of 4-nitrophenol in the presence of NaBH₄, and it can be easily separated from the liquid-phase reaction system during the reusing cycles.     

Crown ether complex cation ionic liquids: preparation and applications in organic reactions

A series of crown ether complex cation ionic liquids (CECILs) were designed, synthesised and characterised by NMR spectroscopy, HRMS, thermogravimetric differential thermal analysis (TG-DTA) and elemental analysis. Their applications in various organic reactions were investigated: [15-C-5Na][OH], [15-C-5Na][OAc], [18-C-6K][OH] and [18-C-6K][OAc] (15-C-5=[15]crown-5; 18-C-6=[18]crown-6) efficiently catalysed the Michael addition of alkenes and relevant nucleophiles; [18-C-6K][OH] and [15-C-5Na][OH] effectively catalysed the Henry reaction of nitromethane and aromatic aldehydes; [18-C-6K][OH] has excellent catalytic efficiency for Knoevenagel condensation of aromatic aldehydes and malononitrile; PdCl(2) /[18-C-6K](3)[PO(4)]/K(2)CO(3) efficaciously catalysed the Heck reaction of olefins and aromatic halides; [18-C-6K][BrO(3)] can be used as both oxidant and solvent in the oxidation reaction of aromatic alcohols. The CECIL catalysts [15-C-5Na][OH] (Michael addition) and [18-C-6K][OH] (Henry reaction) can be recycled and reused several times without obvious loss of activity and their recovery is very simple.     

Recent applications of N-sulfonyloxaziridines (Davis oxaziridines) in organic synthesis

N-Sulfonyloxaziridines are the most commonly used oxaziridines in organic synthesis. Most applications of these stable, commercially available reagents involve the stereo- and regioselective oxidation of nucleophiles which have found many applications in the synthesis of architecturally complex molecules. In addition, these oxaziridines have been used in cycloaddition reactions (oxyamination), epoxidation of alkenes, silyl enol ethers and enamines, as well as C-H oxidation and amination reactions. The object of this review is to highlight recent applications of N-sulfonyloxaziridines in organic synthesis.     

Photomediated core modification of organic photoredox catalysts in radical addition: mechanism and applications

Dihydrophenazines and their analogues have been widely used as strong reducing photoredox catalysts in radical chemistry, such as organocatalyzed atom transfer radical polymerization (O-ATRP). However, when dihydrophenazines were employed as organic photoredox catalysts (OPCs) to mediate O-ATRP, the initiator efficiency was nonquantitative due to cross-coupling between dihydrophenazines and radical species. Here, a new kind of core modification for dihydrophenazines, phenoxazines and phenothiazines was developed through this cross-coupling process. Mechanistic studies suggested that the radical species would be more likely to couple with OPC'' radical cations rather than the ground-state OPC. Core modification of OPCs could stabilize the radical ions in an oxidative quenching catalytic cycle. Significantly, core modifications of OPCs could lower the energy of light required for photoexcitation. Compared with their noncore-modified counterparts, all the core-modified dihydrophenazines and phenoxazines exhibited efficient performance in controlling O-ATRP for the synthesis of poly(methyl methacrylate) with higher initiator efficiencies under the irradiation of simulated sunlight.

Photomediated core modification of organic photocatalysts through a radical/radical cation cross-coupling process enables the ability to stabilize radical ions and prevent undesirable side reactions.     

Synthesis of ‘thianthrene dimer’ by the coupling reaction of stannylthianthrenes in the presence of copper catalysts

The coupling reaction of 1-tributylstannylthianthrene (5) and 2-tributylstannylthianthrene (7) in the presence of copper catalysts at rt afforded the thianthrene dimer 1,1′-bithianthrene (3), 2,2′-bithianthrene (8), and 1,2′-dithianthrene (9) in high yields. Also we obtained thianthrene oxide dimer (R,R) (S,S)-1-(10-S-monoxythianthrene-1-yl)thianthrene-10-S-monoxide (12) and (R,S) (S,R)-1-(10-S-monoxythianthrene-1-yl)thianthrene-10-S-monoxide (13) from 1-tributylstannyl-10-S-monoxythianthrene (10) under the same reaction condition. The final structural conformation of 3, 8, 9, and 12 was performed by X-ray crystallographic analysis. Further, the solvent effects in the coupling reactions were also examined.     

Silicon tetrachloride in organic synthesis: new applications for the vinylogous aldol reaction

This paper describes a novel and efficient methodology for vinylogous aldol reactions based on SiCl₄ catalysis. According to the nucleophilicity Mayr's scale, vinylogous aldol reaction of Chan's diene proved to be effective by using catalytic amount of SiCl₄, without any other promoter. On the contrary, the SiCl₄/Lewis base system has been conveniently exploited for the efficient and selective vinylogous reaction of less nucleophilic Danishefsky's diene and 2-trimethylsilyloxyfuran (TMSOF). Indeed, a number of Lewis bases, such as sulfoxides, formamides and phosphoramides have been successfully used as SiCl₄ promoters. TMSOF and silyloxydienes, resulting from 2,2,6-trimethyl-[1,3]-dioxin-4-one derivatives, required stoichiometric amount of SiCl₄, while vinylogous aldol reaction of Chan's and Danishefsky's dienes took satisfactorily place in the presence of catalytic or sub-stoichiometric amount of catalyst.     

Synthesis and X‐ray Crystal Structures of Zinc Complexes Supported by Chelating Ligands: Various Reactions of α‐Iminopyridines with ZnEt2

α‐Iminopyridine (α‐IP) is an important redox‐noninnocent ligand. The substituents on the imino function of α‐IPs have important impact on the reaction selectivity with diethylzinc. For the α‐IPs with a hydrogen substituent on the imino carbon, reduction occurred for the non‐bulky N‐substituents phenyl and 2‐methylphenyl groups, whereas alkyl addition and coupling reactions can be selectively achieved for the sterically bulky N‐substituents 2,6‐dimethylphenyl or 2,4,6‐trimethylphenyl group. However, for the α‐IPs with a CH₃ substituent on the imino carbon, the deprotonation reaction happened regardless of the N‐substituents of 2‐methylphenyl or 2,6‐dimethylphenyl group. All the products were isolated and characterized by single‐crystal X‐ray diffraction. The possible mechanisms of these reactions were also discussed.