1,4-Cyclohexadiene with Pd/C as a rapid, safe transfer hydrogenation system with microwave heating

A method for the rapid, safe hydrogenation of alkenes and deprotection of benzyl ethers and carboxybenzyl amides is described using catalytic transfer hydrogenation under microwave heating conditions. Commonly available Pd/C catalyst is extremely effective with 1,4-cyclohexadiene as the hydrogen transfer source. In general, the reactions are complete within five minutes at 100 °C.     

Magnetically recoverable supported ruthenium catalyst for hydrogenation of alkynes and transfer hydrogenation of carbonyl compounds

A ruthenium (Ru) catalyst supported on magnetic nanoparticles (NiFe₂O₄) has been successfully synthesized and used for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The catalyst shows excellent selectivity toward the desired products with very high yield even after five repeated uses.     

Recent topics of transfer hydrogenation

A number of transition metal catalysts have been developed for transfer hydrogenation of organic molecules. This method provides a useful process for the reduction of unsaturated molecules without the need for explosive hydrogen gas. An important development in this area is the design of new ligands that improve activity and selectivity under mild reaction conditions. Polydentate ligands are good candidates for producing high performance metal catalysts. This digest describes recent developments in transfer hydrogenation as well as asymmetric reactions using metal catalysts containing polydentate ligand systems.     

Chiral ferrocenyl diphosphines for asymmetric transfer hydrogenation of acetophenone

The synthesis of new optically pure ferrocenyl diphosphines have been realized from (R)-(+)-N,N-dimethylaminoethylferrocene. Particularly, dissymmetric ferrocenyl diphosphines have been synthesized. The diphosphines have been used as ligands in asymmetric transfer hydrogenation of acetophenone in the presence of Ru catalysts.     

Selective debenzylation of aromatic benzyl ethers by silica-supported sodium hydrogen sulfate

A new debenzylation of aromatic benzyl ethers by silica-supported sodium hydrogen sulfate is described. The process proceeds selectively and efficiently in good to excellent yields without affecting sensitive functional groups such as nitro, COOMe, aldehyde, ketone, and tosyl.     

Regio- and chemoselective transfer hydrogenation of quinolines catalyzed by a CpIr complex

An efficient method for the transfer hydrogenation of quinolines catalyzed by a Cp^∗Ir complex was developed. A variety of 1,2,3,4-tetrahydroquinolines were obtained by regio- and chemoselective transfer hydrogenation of quinolines using 2-propanol as a hydrogen source.     

Optimisation and scale-up of microwave assisted cyanation

A microwave enhanced palladium catalysed cyanation procedure was optimised for the final step of a production method for citalopram 2. The method was demonstrated on multigram batch scale for the synthesis of escitalopram (S)-2 and then in a stop-flow continuous process for citalopram.     

Transition metal free transfer hydrogenation of ketones promoted by 1,3-diarylimidazolium salts and KOH

An efficient transition metal free and greener catalytic system was developed for the selective transfer hydrogenation of saturated ketones to alcohols. This was achieved by the use of 1,3-diarylimidazolium salts in the presence of KOH as a promoter for the reaction. When the range of substrates was expanded to include unsaturated ketones, selective reduction of the double bond occurred. The catalyst efficiency was comparable to some established transition metal catalyzed systems. The current system utilizes mild aerobic reaction conditions compared to the inert atmosphere conditions required for the corresponding metal based systems.     

Theoretical investigation on the mechanisms of transfer hydrogenation of ketones catalyzed by iridium complexes

The detailed catalytic mechanisms on transfer hydrogenation of ketones are explored by employing the representative reaction of 3-pentanone and 2-propanol catalyzed by the model complex IrH₃[(Me₂PC₂H₄)₂NH], derived from the catalyst IrH₃[(ⁱPr₂PC₂H₄)₂NH], with the aid of the density functional theory calculations. The geometrical transformation from an octahedron to a Y-type involved in the catalytic cycle is also elucidated in terms of molecular theory of transition metal complexes. The trend for the variation of Ir-N bond distance is also analyzed.     

氧掺入MoS2调节芳香硝基化合物选择性转氢还原

芳香胺类化合物及其衍生物是一类重要的有机合成中间体,广泛应用于染料、农药、医药及其他精细化学品.目前催化芳香硝基化合物还原制备芳香胺的多相催化体系多使用含有d6-d10贵金属以及高活性Ni的催化剂.为了提高反应的选择性,金属纳米颗粒的尺寸控制、合金效应、金属载体强相互作用、溶剂以及添加剂的筛选等不同手段被采用.考虑到该类催化剂复杂的制备方法以及易氧化的性质,近年来稳定高效的非贵金属体系的开发得到了广泛关注.MoS2是一类重要的高温加氢催化剂,不饱和的Mo位点(CUS Mo)被认为在催化过程中起到了关键性作用.但是理论与实践已经证明,作为代表性的二维材料,MoS2的活性位点多集中于层状结构的边楞结构处.占有最大暴露面积的基面结构因为稳定的Mo-S化学键组成在化学反应中多表现为催化惰性.通过剥离的手段可以有效提升活性位点的数目,但新增的活性位点仍然多集中于层状结构的边楞结构处而不是基面.在MoS2与MoO2结构中Mo-S和Mo-O的键长不同,同时S和O的配位形式也不同.可以预见的是,如果MoS2结构中的一部分S元素被O元素取代,在这样的材料中将会出现大量缺陷以及活性CUS Mo结构.结合先前关于硫化钼材料的制备方法,我们通过部分硫化还原[Mo7O24]6-前驱物的方法制备了氧掺杂的MoS2材料(标记为O-MoS2).通过XRD,XPS,Raman和EDX等表征发现,不同的Mo-O结构存在于O-MoS2材料中.HRTEM表征结果显示,O-MoS2表面存在着丰富的结构缺陷.EXAFS结果显示,O-MoS2材料中可能含有四配位以及五配位的CUS Mo结构.以甲酸铵还原硝基苯为探针反应检测了CUS Mo结构.发现O-MoS2可以在水相条件下高效催化芳香硝基化合物还原生成相应的芳香胺,且催化剂稳定,可以多次循环使用.结合对照不同催化剂的NH3-TPD数据以及MoS2结构模型,我们发现O-MoS2材料中含有丰富的CUS Mo结构,这些CUS Mo结构更多地存在于材料的基面而非边楞结构.我们认为,对于该类掺杂MoS2材料的制备及结构表征将有利于拓宽MoS2催化剂从高温气相反应到温和液相反应中的应用.     

Structure–reactivity relationship in transfer hydrogenation of aliphatic ketones over magnesium oxide

The vapour phase reduction of various aliphatic ketones to the corresponding carbinols by propan-2-ol in the presence of MgO as a catalyst has been studied. A strong decrease of the reactivity (from 86 to 0%) in the reduction of pentan-3-one and its polymethyl derivatives with an increase of the bulkiness of both alkyl groups in the ketone has been observed. For ketones with the general formula CH₃-(CH₂)_n-CO-(CH₂)_8–n-CH₃, where n = 0, 1, 2, 3 and 4, a shift of the carbonyl group to the middle of a molecule causes only a small decrease of the reactivity. It has been stated that the observed changes in the reactivity of ketones are mainly caused by a steric hindrance around their carbonyl groups.     

Carbon dioxide hydrogenation to formic acid by using a heterogeneous gold catalyst

AUROlite, consisting of gold supported on titania (picture shows extrudates in a steel net cage), is a robust catalyst for the production of catalyst-free HCOOH/NEt(3) adducts from H(2), CO(2), and neat NEt(3). Pure HCOOH is freed from the adducts by amine exchange.     

Upgrading and expanding the scope of homogeneous transfer hydrogenation

Transfer hydrogenation using inexpensive and safe hydrogen sources of alcohols and formic acid has been studied thoroughly over the decades. In particular, the asymmetric version offers the state-of-the-art methods to obtain optically active alcohols and amines, which are valuable synthetic intermediates in the field of pharmaceutical and agrochemical industry. This digest paper highlights the recent notable advances in homogeneous transfer hydrogenation using transition metal complexes, especially in direction to establish practical greener processes by upgrading the catalyst performance or by expanding the scope of reducible functional groups.     

pH-Regulated transfer hydrogenation of quinoxalines with a Cp*Ir-diamine catalyst in aqueous media

The combination of [Cp*IrCl₂]₂ with N-(2-aminoethyl)-4-(trifluoromethyl)benzenesulfonamide constitutes an efficient catalyst for selective transfer hydrogenation of a variety of quinoxalines in water with HCOONa as the hydrogen source, affording the corresponding tetrahydroquinoxalines in good to excellent yields. The catalyst is air-stable, and the reduction could be performed without nitrogen protection. The aqueous phase reduction is shown to be highly pH-dependent, with acidic pH leading to better results. There exits a pH window for optimum rate, and the use of HOAc/NaOAc buffer solution is essential for maintaining a stable pH during the reaction.     

Ruthenium(II) pincer complexes with oxazoline arms for efficient transfer hydrogenation reactions

Well-defined P^NN^CN pincer ruthenium complexes bearing both strong phosphine and weak oxazoline donors were developed. These easily accessible complexes exhibit significantly better catalytic activity in transfer hydrogenation of ketones compared to their PN³P analogs. These reactions proceed under mild and base-free conditions via protonation-deprotonation of the ‘NH’ group in the aromatization-dearomatization process.     

Quinoline-functionalized N-heterocyclic carbene complexes of iridium: Synthesis, structures and catalytic activities in transfer hydrogenation

Iridium complexes containing quinoline-functionalized N-heterocyclic carbene (NHC) ligands have been synthesized by the transmetalation route from silver carbene precursors. The silver complexes undergo a facile reaction with [Ir(COD)Cl]₂ (COD = 1,5-cyclooctadiene) to yield a series of carbene complexes [(NHC)Ir(COD)Cl] (NHC = 3-methyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2a); 3-n-butyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2b); 3-benzyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2c); 1,3-di(8-quinolylmethyl)imidazole-2-ylidene (2d). The coordinated COD was replaced by carbon monoxide to yield the corresponding carbonyl species [(NHC)Ir(CO)₂Cl] (3). Complexes 2 and 3 have been characterized by IR, ESI-MS, ¹H and ¹³C NMR and elemental analyses. The molecular structures of complexes 2b and 2c have been confirmed by single-crystal X-ray diffraction. Two analogous Ir(I) complexes 5 and 6 with naphthalene-containing NHC have also been synthesized and characterized. These Ir(I) complexes in the current work have been proved to be active catalysts in the transfer hydrogenation of ketones to alcohols using 2-propanol as the hydrogen source.     

Palladium-catalysed transfer hydrogenation of aromatic nitro compounds — an unusual chain elongation

Aromatic nitro compounds are reduced via transfer hydrogenation in the presence of palladium on magnesium-lanthanum mixed oxide support in ethanol yielding the corresponding amines. With several acetophenone derivatives, the reduction was accompanied by chain elongation whilst the carbonyl group remained intact.     

Enantioselective transfer hydrogenation of ketones with planar chiral ruthenocene-based phosphinooxazoline ligands

1,2-Disubstituted planar chiral ruthenocene-based phosphinooxazoline ligands (Rc-PHOX, 3 and 4) were synthesized easily and applied in the transfer hydrogenation of ketones to chiral alcohols using 2-propanol as a source of hydrogen with excellent enantioselectivity and high catalytic activity.     

Fast oxidation of secondary alcohols by the bromate-bromide system using cyclic microwave heating in acidic water

We report an improved, gentle, cyclic microwave activation technique for the oxidation of secondary alcohols using nonhazardous hypobromous acid (BrOH) as the reagent in acidic water. Several aliphatic and aromatic secondary alcohols were successfully oxidized to the corresponding ketones using this technique in high yields and with only minor amounts of side products.     

氰基化合物非均相加氢制备有机胺的研究进展

介绍了不同结构的氰基化合物加氢还原制备有机胺的研究工作,重点对用非均相催化剂的氰基化合物加氢研究现状进行了综述,指出高性能催化剂的开发仍是今后研究的主要方向。