NCP‐Type Pincer Iridium Complexes Catalyzed Transfer‐Dehydrogenation of Alkanes and Heterocycles†

A series of NCP‐type pincer iridium complexes, (^RNC^CP)IrHCl ( 2a — 2c ) and (^BQ‐NC^OP)IrHCl 3 , have been studied for catalytic transfer alkane dehydrogenation. Complex 3 containing a rigid benzoquinoline backbone exhibits high activity and robustness in dehydrogenation of alkanes to form alkenes. Even more importantly, this catalyst system was also highly effective in the dehydrogenation of a wide range of heterocycles to furnish heteroarenes.     

Dehydrogenation of a combined LiAlH4/LiNH2 system

Although there have been numerous materials systems studied as potential candidates for hydrogen storage applications, none of the materials known to date has demonstrated enough hydrogen capacity or efficiency at required operating temperature ranges. There are still considerable opportunities for discovery of new materials or material systems that could lead to advances in science as well as commercial technologies in this area. LiAlH(4) is one of the most promising materials owing to its high hydrogen content. In the present work, we investigated dehydrogenation properties of the combined system of LiAlH(4) and LiNH(2) under atmospheric argon. Thermogravimetric analysis (TGA) of 2LiAlH(4)/LiNH(2) mixtures without any catalysts indicated that a large amount of hydrogen (approximately 8.1 wt %) can be released between 85 and 320 degrees C under a heating rate of 2 degrees C/min in three dehydrogenation reaction steps. It is found that LiNH(2) effectively destabilizes LiAlH(4) by reacting with LiH during the dehydrogenation process of LiAlH(4).     

Oxygen‐Assisted Hydroxymatairesinol Dehydrogenation: A Selective Secondary‐Alcohol Oxidation over a Gold Catalyst

Selective dehydrogenation of the biomass‐derived lignan hydroxymatairesinol (HMR) to oxomatairesinol (oxoMAT) was studied over an Au/Al₂O₃ catalyst. The reaction was carried out in a semi‐batch glass reactor at 343 K under two different gas atmospheres, namely produced through synthetic air or nitrogen. The studied reaction is, in fact, an example of secondary‐alcohol oxidation over an Au catalyst. Thus, the investigated reaction mechanism of HMR oxidative dehydrogenation is useful for the fundamental understanding of other secondary‐alcohol dehydrogenation over Au surfaces. To investigate the elementary catalytic steps ruling both oxygen‐free‐ and oxygen‐assisted dehydrogenation of HMR to oxoMAT, the reactions were mimicked in a vacuum over an Au₂₈ cluster. Adsorption of the involved molecular species—O₂, three different HMR diastereomers (namely, one SRR and two RRR forms), and the oxoMAT derivative—were also studied at the DFT level. In particular, the energetic and structural differences between SRR‐HMR and RRR‐HMR diastereomers on the Au₂₈ cluster were analyzed, following different reaction pathways for the HMR dehydrogenation that occur in presence or absence of oxygen. The corresponding mechanisms explain the higher rates of the experimentally observed oxygen‐assisted reaction, mostly depending on the involved HMR diastereomer surface conformations. The role of the support was also elucidated, considering a very simple Au₂₈ charged model that explains the experimentally observed high reactivity of the Au/Al₂O₃ catalyst.     

化学计量比和放氢背压对LiBH4+xMg2NiH4体系放氢性能的影响

研究了不同化学计量比(x=0.25, 0.5, 0.75, 1.0, 1.25)和放氢背压(1×10-4和0.4 MPa)对LiBH4+xMg2NiH4复合体系吸放氢性能的影响. 结果表明, 随着化学计量比(x)的增加, 复合体系的放氢温度逐渐降低, 放氢动力学性能得到提高, 但放氢容量逐渐降低; 其中, 在1×10-4和0.4 MPa初始放氢背压下, LiBH4+0.75Mg2NiH4体系具有最佳放氢动力学性能和较高的储氢容量. 结果表明, 放氢背压和化学计量比均会对高温下液相LiBH4 与固态Mg2NiH4 的润湿性产生影响, 进而影响复合体系的放氢路径和放氢动力学性能.     

Dehydrogenation of 4-phenyl-substituted spinaceamine and spinacine

The dehydrogenation of 4-phenyl-substituted spinaceamine and spinacine with elemental sulfur in dimethylformamide at 120–150°C leads to the corresponding imidazo[4,5-c]pyridines. Sulfur may be regarded as a specific reagent for oxidative decarboxylation which accompanies dehydrogenation of 4-phenyl-substituted spinacine derivatives.     

Spontaneous dehydrogenation of 2-hydrazinoethyl- and 4-hydrazinobut-2-enylphosphonium salts

2-Hydrazinoethyl- and 4-hydrazinobut-2-enylphosphonium salts undergo spontaneous dehydrogenation leading to the corresponding hydrazones or diazenes, depending on the structure of the starting compounds or the reaction conditions. A possible mechanism of the trans-formations is discussed.     

TiF3对LiAlH4放氢性能的影响

采用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)和热重(TG)等测试方法, 对掺杂TiF₃前后和不同TiF₃掺杂量LiAlH₄的放氢性能进行了研究. 结果发现, 在TiF₃存在下, LiAlH₄在球磨过程中有少量分解. TiF₃对LiAlH₄放氢具有明显的催化作用. 随着掺杂量的增加, LiAlH₄的起始放氢温度降低, 但放氢量会明显减少. 掺杂2%(摩尔分数)TiF₃的LiAlH₄从80 ℃开始放氢, 比未处理的LiAlH₄的起始放氢温度降低了70 ℃, 放氢量高达6.6%(质量分数).     

LiAlH4与LiNH2的相互作用机理及储氢特性

将LiAlH4和LiNH2按摩尔比1：2进行球磨复合,随后将复合物进行加热放氢特性研究,然后对其完全放氢后的产物进行再吸氢特性研究。通过X射线衍射分析(XRD)、热分析(DSC)和红外 (FTIR)分析等测试手段对其反应过程进行了系统分析研究。研究结果表明,LiAlH4/2LiNH2加热放氢分为3个反应阶段,放氢后生成Li3AlN2,总放氢量达到8.65wt%。放氢生成的Li3AlN2在10MPaH2压力和400℃条件下,可以可逆吸氢5.0wt%,吸氢后的产物为 LiNH2 、AlN和LiH,而不能再生成LiAlH4。本文对LiAlH4/2LiNH2复合物放氢/再氢化过程机理进行了分析。     

Synthesis and dehydrogenation of spinaceamine and spinacine 4-hetaryl derivatives

The reaction of histamine and histidine with various hetarylaldehydes under the conditions of the base-catalyzed Pictet-Spengler process affords 4-hetaryl-substituted derivatives of spinaceamine and spinacine. The dehydrogenation of the 4-hetaryl-substituted spinaceamine derivatives using elemental sulfur in DMF at 120–130°C led to the formation of 4-hetaryl derivatives of imidazo[4,5-c]-pyridine. Under similar conditions the 4-hetaryl-substituted spinacine derivatives suffered both the dehydrogenation and oxidative decarboxylation resulting in the products identical to the compounds obtained by the dehydrogenation of 4-hetaryl-substituted spinaceamine.     

Pyrolysis-gas chromatography-mass spectrometry of tricyclic hydroaromatic compounds from coal hydrogenates

Pyrolysis—gas chromatography—mass spectrometry of perhydrophenanthrene, perhydroanthracene and 9,10-dihydrophenanthrene was carried out between 700 and 1000°C in order to study their conversion into light aromatics. The results show that the total hydrogenation of the rings has a great influence on the yields of monoaromatics, obtained by cleavage of the rings and recombination of the fragments. The partially hydrogenated compounds undergo a dehydrogenation reaction, leading back to the stable polycyclic aromatic.     

Effect of substituents on the nature of the products of oxidation of 4H-thiopyrans

Depending on the degree of substitution of the thiopyran ring, either oxidation at the sulfur atom, which leads to the formation of the 1,1-dioxide, or dehydrogenation of the heteroring in the C₍₄₎ position may occur in the reaction of 4H-thiopyrans with hydrogen peroxide in acetic acid. In the case of dehydrogenation the composition of the products depends on the nature of the starting 4H-thiopyran. Some peculiarities of the structure of 4H-thiopyrans that promote their conversion to 1,1-dioxides were ascertained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1042–1046, August, 1985.     

Oxidation of 4-chromanones with thallium(III) nitrate

Treatment of 4-chromanones 1a-g with thallium(III) nitrate in acidic methanol results mainly in dehydrogenation, whereas α-methoxylation and/or Taylor-McKillop rearrangement predominate in trimethyl orthoformate. The mechanistic features of these oxidations are briefly discussed.     

3LiBH4/CeF3体系的放氢性能及机制

采用球磨法制备了3LiBH₄/CeF₃反应体系, 通过压力-组成-温度(PCT)测试仪、 X射线衍射仪(XRD)和傅里叶变换红外光谱仪(FTIR)研究了体系的放氢性能、 反应机制及性能改善机理. 结果表明, 3LiBH₄/CeF₃体系在295 ℃左右快速放氢, 总放氢量为4.1%(质量分数). 放氢过程中CeF₃与LiBH₄直接发生反应: 3LiBH₄+CeF₃1/2CeB₆+1/2CeH₂+3LiF+11/2H₂. 与纯LiBH₄相比, 放氢热力学稳定性和表观活化能的降低是3LiBH₄/CeF₃体系放氢温度下降的主要原因.     

Pressure-enhanced dehydrogenation reaction of the LiBH4-YH3 composite

The increase in hydrogen back pressure unexpectedly enhances the overall dehydrogenation reaction rate of the 4LiBH(4) + YH(3) composite significantly. Also, argon back pressure has a similar influence on the composite. Gas back pressure seems to enhance the dehydrogenation reaction by kinetically suppressing the formation of the diborane by-product.     

Superior hydrogen storage properties of LiBH4 catalyzed by Mg(AlH4)2

Mg(AlH(4))(2) is found to provide a synergistic effect on improving the de-/rehydrogenation properties of LiBH(4). The Mg(AlH(4))(2)-catalyzed LiBH(4) exhibits lower dehydrogenation temperature and faster de-/rehydrogenation kinetics than the individually MgH(2)- or Al-catalyzed LiBH(4).     

Synthesis of 4''''-Methoxy Flavone

Theflav0nesare0btainedmainlyfr0mnature,sec0ndlybybiol0gicalsynthesis.ThechemicaIsynthesisiscarried0utm0stIybycyclizati0nandc0ndensati0n0f0-hydroxyacet0phe11one"',orbydehydr0genati0n0fflavanones4'5'6.Herewerep0rtanewsyntheticmethod0fflav0nesbythereacti0n0fenamineandheptanedioylchIoride.AcyIation0f2m0Ieenaminewithlm0lechl0ride0fdicarb0xylicacidhasbeenusedt0preparebis-(l,3-diket0ne)compound',butwediscoveredthat4'-methoxy-5,6,7,8-tetrahydroflav0nepreparedbyreacti0n0f4-meth0xyacet0phen0neenamine…     

Palladium-promoted formation of cyclohexenonitriles from 1-hexene and acrylonitrile

Acrylonitrile and 1-hexene react in the presence of palladium on charcoal to give four isomers of 3,6-dimethylcyclohexenonitriles along with 2,5-dimethylbenzonitrile. The reaction probably involves palladium-promoted dehydrogenation of 1-hexene to 2,4-hexadienes followed by a Diels—Alder reaction between 2,4-hexadiene and acrylonitrile. The structures of the main products are discussed.     

Physiochemical pathway for cyclic dehydrogenation and rehydrogenation of LiAlH4

A five-step physiochemical pathway for the cyclic dehydrogenation and rehydrogenation of LiAlH4 from Li3AlH6, LiH, and Al was developed. The LiAlH4 produced by this physiochemical route exhibited excellent dehydrogenation kinetics in the 80-100 degrees C range, providing about 4 wt % hydrogen. The decomposed LiAlH4 was also fully rehydrogenated through the physiochemical pathway using tetrahydrofuran (THF). The enthalpy change associated with the formation of a LiAlH4.4THF adduct in THF played the essential role in fostering this rehydrogenation from the Li3AlH6, LiH, and Al dehydrogenation products. The kinetics of rehydrogenation was also significantly improved by adding Ti as a catalyst and by mechanochemical treatment, with the decomposition products readily converting into LiAlH4 at ambient temperature and pressures of 4.5-97.5 bar.     

多取代芳香族化合物的合成 4.取代的环丁-3-烯砜与丁炔二酸二甲酯的Diels-Alder反应

３－苯硒基－或３－苯硫基取代的环丁－３－烯砜甚易与丁炔二酸二甲酯发生Ｄｉｅｌｓ－Ａｌｄｅｒ反应，生成相应的苯硒基或苯硫基取代的１，４－环己二烯－１，２－二羧酸二甲酯，此类产物用二氯二氰苯醌（ＤＤＱ）处理，即生成相应的多取代芳香族化合物４－苯硒基邻苯二甲酸二甲酯或４－苯硫基邻苯二甲酸二甲酯。     

The Li+-Initiated Twofold Dehydrogenation and C−C Bond Formation of Hexaphenylbenzene to the Dilithium Salt of the 9,10-Diphenyltetrabenz[a,c,h,j]anthracene Dianion

Partly solvent-separated and partly solvent-shared , the contact ion triple of the 9,10-diphenyltetrabenz[a,c,h,j]anthracene dianion is formed by the ultrasonically activated reaction of hexaphenylbenzene with lithium metal powder in 1,2-dimethoxyethane (dme) [Eq. (1)]. The proposed microscopic pathway for this reaction—twofold dehydrogenation and C−C bond formation—is supported by quantum-chemical calculations.