单核第一过渡周期金属水氧化催化剂（英文）

由于传统化石能源的不可再生性,其储量日益减少.同时,传统化石能源的使用对环境产生了巨大影响,给人类社会带来了一系列问题,包括温室效应、酸雨等.因此,进入二十一世纪以后,人类面临着日益严峻的能源危机和环境问题,寻找清洁、高效的替代能源已经迫在眉睫.太阳能被认为是一种洁净的可再生能源.自然界通过光合作用将太阳能转化为化学能,在这一过程中,水被氧化产生氧气,同时释放出的电子和质子通过和二氧化碳作用生成碳水化合物.为了模拟这一过程,人工光合作用可以直接将电子和质子结合形成氢气.由此生成的氢气也被认为是洁净的可再生能源,因为在其燃烧过程中只产生水.因此,通过光致水分解析氢析氧的人工光合作用受到了越来越广泛的重视.水分解可以分为两个独立的半反应,即水的氧化析氧和水的还原析氢.水的氧化无论在热力学还是动力学方面,都存在着非常大的阻碍.在热力学上,两分子的水氧化生成一分子氧气需要提供很多能量(ΔE=1.23 V vs NHE).在动力学上,由于涉及到四个氢原子和两个氧原子的重组,并且涉及到氧氧键形成并释放出一分子氧气,因此水氧化是一个非常缓慢的过程.在自然界,水的氧化主要发生在光合作用中,在绿色植物的叶绿体中完成.通过对光合作用的研究,科学家们发现氧气的产生由光系统Ⅱ(PSII)中的释氧中心来完成.释氧中心是一个钙锰簇合物,由四个锰和一个钙组成(Mn_4CaO_x).自然界水分解产生氧气的过程给了我们很大启示,对设计和研究高效稳定的水氧化催化剂具有一定的指导意义.目前水氧化催化剂主要有两大类.第一类是基于材料的水氧化催化剂.该类催化剂的催化效率高,过电势小,但是对水氧化催化过程的机理缺乏深入研究.第二类是基于金属配合物的分子催化剂.相比基于材料的催化剂,分子催化剂具有以下特点:(1)分子催化剂的结构可以通过实验手段表征清楚;(2)可以结合光谱对水氧化的机理进行深入研究,可以对催化过程中间体进行表征;(3)催化剂的结构可以从分子水平上进行修饰,因此可以更好地研究催化效率与结构之间的关系,为设计高效、稳定的催化剂提供必要信息;(4)比较容易组装成分子器件从而应用到实际的水氧化装置中;(5)通过实验与理论的结合,对氧氧成键提出新的认识与理解.近几年来,一些单核的金属配合物逐渐被发现可以高效、稳定地催化水氧化.研究表明,一些基于钌和铱的催化剂具有良好的催化活性,但由于金属钌和铱储量少、价格昂贵等因素,限制了该类催化剂的大量使用.由于第一过渡系金属元素具有储量丰富、安全无毒、廉价易得等优势,第一过渡周期金属化合物逐渐成为科学家们研究的热点.近几年来,基于第一过渡系金属的水氧化催化剂已经有大量报道.本文主要总结了近几年来基于第一过渡系金属的单核水氧化分子催化剂.通过对催化机理进行深入的讨论,特别是对氧氧成键的总结,本文将对设计合成结构新颖、具有高催化效率和良好稳定性的水氧化分子催化剂提供理论依据.     

Orthopalladated complexes as phase-transfer catalysts for asymmetric alkylation of achiral Schiff base esters

The asymmetric C-alkylation of benzophenone Schiff base glycine esters has been achieved using a palladium(II) chiral complex as a phase-transfer catalyst. The aromatic moiety around the metal center and various physicochemical parameters were investigated to study their effect on the asymmetric alkylation reaction under phase-transfer conditions. Moderate enantioselectivity(30–40%) was achieved under room temperature conditions, which is a significant improvement compared to no enantioselectivity with a chiral palladium-salen complex reported earlier. Computer simulation studies indicate that coordination of the metal center with Z-enolate forming a square planar complex provides a favorable steric environment where the α-carbon atom of the enolate is available for enantioselective alkylation.     

Dinuclear metal complexes of Schiff base ligands as catalysts for oxidation and epoxidation reactions

Dinuclear copper(II) complexes (Cu₂ L_nCl₃), nickel(II) complexes (Ni₂ L_nCl₃) and cobalt(II) complexes (Co₂L ₂ ⁿ Cl₂) from Schiff base ligands are synthesised, characterised and used as catalysts for oxidation of 3,5-DTBC to 3,5-DTBQ. (Cu₂L_nCl₃) are found to be more efficient than the other complexes. Dinuclear iron(III) complexes of composition (Fe₂L₂Cl₂) and ruthenium (III) complexes of composition Ru₂L ₂ ⁿ Cl₆(PPh₃)₂ and Ru₂L ₂ ⁿ Cl₂(PPh₃)₂ catalyse epoxidation of styrene and cyclohexene. Catalytic activities of ruthenium(III) complexes are much greater than those of analogous iron(III) complexes.     

Ruthenium complexes bearing bidentate Schiff base ligands as efficient catalysts for organic and polymer syntheses

A concise overview is given on mononuclear and dinuclear, bidentate Schiff base ruthenium complexes with different additional ligands and on their applications in various chemical transformations such as Kharasch addition, enol-ester synthesis, alkyne dimerization, olefin metathesis and atom transfer radical polymerization. These new ruthenium complexes, conveniently prepared from commonly available ruthenium compounds, are very stable, exhibit a good tolerance towards organic functionalities, air and moisture and display high activity and chemoselectivity in chemical transformations. Relevant features of coordination chemistry connected with the reaction mechanism and chemoselectivity are also fully described. Since the nature of Schiff bases can be changed in a variety of ways, appealing routes for designing and preparing novel ruthenium complexes can be foreseen in the future.     

Studies on ruthenium(II) Schiff base complexes as catalysts for transfer hydrogenation reactions

The reactions of [RuHCl(CO)(B)(EPh₃)₂] (B = EPh₃ or Py; E = P or As) and Schiff bases in 1:1 molar ratio led to the formation of [RuCl(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃, AsPh₃ or Py; L = Schiff base ligand). The new complexes have been characterized by analytical and spectroscopic (IR, electronic and ¹H NMR) data. They have been assigned an octahedral structure. The new complexes were found to catalyse the transfer hydrogenation of ketones.     

Acetamidine complexes as catalysts for ethylene polymerization

The reaction of (2,6-diisopropyl-phenyl)-acetimidoyl chloride or (2,6-dimethyl-phenyl)-acetimidoyl chloride with 2,6-dimethylaniline in the presence of triethylamine yields a mixture of isomers N′-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine (1a) and N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N′-(2,6-dimethyl)-acetamidine (1b), and N,N′-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine (2), respectively. The addition of isomers (1a + 1b) to nickel (II) dibromide 2-methoxyethyl ether, (NiBr₂[O(C₂H₄OMe)₂]) gives a mixture of new nickel complexes, [NiBr₂{N′-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine}] (3a) and [NiBr₂{N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N′-(2,6-dimethyl)-acetamidine}] (3b). Similarly, ligand 2 reacts with nickel (II) dibromide 2-methoxyethyl ether to afford the complex [NiBr₂{N,N´-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine}] (4). The structures of the ligands and nickel complexes have been determined by single crystal X-ray diffraction.The addition of MAO to these complexes generates catalytically active species for the homopolymerization of ethylene. The polymer products are high molecular weight (80-169 K). At temperatures of up to 60 °C both catalysts are a single site giving a monomodal molecular weight distribution. However, at 70 °C the mixture (3a + 3b) shows a bimodal molecular weight distribution.     

Functional zinc(II) phthalocyanines bearing Schiff base complexes as oxidation catalysts for bleaching systems

Oxidation catalysis is used to increase the performance of hydrogen peroxide in laundry bleach applications. Bleach catalysts provide cost‐effective, energy‐saving and environmentally friendly bleach systems yielding perfect stain removal at lower temperatures. This comparative study is based on the synthesis of bis[bis(salicylhydrazonephenoxy)manganese(III)] phthalocyaninatozinc(II) ( 2 ), bis[bis(salicylhydrazonephenoxy)cobalt(III)] phthalocyaninatozinc(II) ( 3 ) and bis[bis(salicylhydrazonephenoxy)iron(III)] phthalocyaninatozinc(II) ( 4 ) as tri‐nuclear complexes consisting of two Schiff base complexes substituting a zinc phthalocyanine. Complexion on the periphery to obtain complexes 2 , 3 , 4 was performed through the reaction of a Schiff base‐substituted phthalocyanine using MnCl₂?4H₂O, CoCl₂?6H₂O or FeCl₃?6H₂O salts in basic condition in dimethylformamide. Fourier transform infrared, ¹H NMR, ¹³C NMR, UV–visible, inductively coupled plasma optical emission and mass spectra were applied to characterize the prepared compounds. The bleach performances of the three phthalocyanine compounds 2 , 3 , 4 were examined by the degradation of morin as hydrophilic dye. The degradation progress in the presence of catalysts 2 , 3 , 4 /H₂O₂ combination in aqueous solution was investigated using an online spectrophotometric method. It was found that the catalysts 2 , 3 , 4 exhibited better bleaching performance at 25 °C than tetraactylethylethylenediamine as bleach activator used in powder detergent formulations for stain removal. Copyright © 2015 John Wiley & Sons, Ltd.     

Ruthenium complexes of Schiff base ligands as efficient catalysts for catechol–hydrogen peroxide reaction

Zeolite Y-encapsulated ruthenium(III) complexes of Schiff bases derived from 3-hydroxyquinoxaline-2-carboxaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYqpd, RuYqap and RuYqab, respectively) and the Schiff bases derived from salicylaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYsalpd, RuYsalap and RuYsalab, respectively) have been prepared and characterized. These complexes, except RuYqpd, catalyze catechol oxidation by H₂O₂ selectively to 1,2,4-trihydroxybenzene. RuYqpd is inactive. A comparative study of the initial rates and percentage conversion of the reaction was done in all cases. Turn over frequency of the catalysts was also calculated. The catalytic activity of the complexes is in the order RuYqap > RuYqab for quinoxaline-based complexes and RuYsalap > RuYsalpd > RuYsalab for salicylidene-based complexes. The reaction is believed to proceed through the formation of a Ru(V) species.     

Ruthenium complexes with chelating carboxylate-NHC ligands as efficient catalysts for CH arylation in water

Ruthenium(ii) complexes with chelating N-heterocyclic carbene (NHC) ligands were studied in the arylation of phenyl group in 2-phenylpyridine and 1-phenylpyrazole with aryl chlorides in water. Complexes with NHC-ligands containing a hemilabile coordinating N-carboxylatomethyl group enable fast and selective ortho-CH-diarylation in the absence of carboxylate-assisting additives.     

Oxorhenium complexes as aldehyde-olefination catalysts

Several oxorhenium compounds in the formal oxidation states V and VII are examined as catalysts for the aldehyde-olefination starting from diazo compounds, phosphines, and aldehydes. Of these, [ReMeO2(eta2-alkyne)] complexes provide the simplest catalysts to study, although [ReOCl3(PPh3)2] still remains the most efficient rhenium catalyst for aldehyde-olefination described to date. Prior to the reaction with the Re catalysts the phosphine and the diazo compound react to form a phosphazine. No catalytic reaction occurs in cases where no phosphazine formation is observed. The first step of the catalytic cycle involves the formation of a carbene intermediate by the reaction of phosphazine and catalyst under extrusion of phosphine oxide and dinitrogen. In a second step the carbene reacts with aldehyde under olefin formation and catalyst regeneration. Excess of alkyne as well as the presence of ketones slows down the catalytic reaction. The olefination of 4-nitrobenzaldehyde with diazomalonate is possible with these Re catalysts. In contrast, this reaction does not take place either in the classical Wittig fashion from Ph3P=C(CO2Et)2 and aldehyde or by use of all other catalysts for aldehyde olefination reactions reported to date. Catalytic ylide formation from diazo compounds seems therefore not to be the only pathway through which catalytic aldehyde-olefination reactions can proceed.     

Chromone-based Schiff base metal complexes as catalysts for catechol oxidation: Synthesis,kinetics and electrochemical studies

Two new Schiff base ligands with chromone moiety and their transition metal complexes were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conductance and TGA analyses, FT IR, UV-Vis, NMR and mass spectroscopy. All the complexes synthesized have been investigated as functional models for catechol oxidase (catecholase) activity by employing 3,5-di-tert-butylcatechol as a model substrate. The two mononuclear copper(II) and two mononuclear iron(II) complexes show catecholase activity with turnover (k_cat) numbers lying in the range 27.2–1328.4 h^?1. According to the kinetic measurement results, the rate of catechol oxidation follows first order kinetics and iron(II) complexes were found to have higher catalytic activity than those of copper(II) complexes. Electron-donating substituent on Schiff base ligand enhanced the catalytic activity of metal complexes while the electron-withdrawing substituent led to a decrease in activity. The electrochemical properties of two Schiff bases and their metal complexes were also investigated by Cyclic Voltammetry (CV) using glassy carbon electrode (GCE) at various scan rates. Electrochemical processes of all the compounds were observed as irreversible.     

Synthesis and characterization of manganese and copper corrole xanthene complexes as catalysts for water oxidation

Two corrole xanthene ligands and four corresponding Mn^IV and Cu^III complexes have been synthesized and spectroscopically characterized. This kind of complexes, comprising of xanthene and corrole linked by an amide bond, were designed as bio-inspired models for the oxygen evolving complex (OEC) in Photosystem II. We find that both manganese complexes 4a and 5a have efficiency on catalyzing oxygen evolution at low potential (about 0.80 V) by electrochemical method, which is a significant progress in the study of dioxygen formation.     

New Schiff base complexes of ruthenium(III) and their use as catalysts for O-allyl systems isomerization

Seven new ruthenium(III) complexes of the general formula [RuCl(PPh₃)LL′] · xH₂O (LL′ = [ONNO] = symmetrical and unsymmetrical Schiff base derivatives of trans-1,2-diaminocyclohexane and 2-hydroxynaphthaldehyde as well as R-salicylaldehydes, x = 0–3) have been synthesized. The complexes were characterized by physico-chemical and spectroscopic techniques. The catalytic activities of the complexes in the isomerization reaction of selected O-allyl systems, i.e., 1,4-diallyloxybutane and 4-allyloxybutan-1-ol have been studied. Some of the complexes showed high efficiency and E-stereoselectivity in double bond migration of allyl group to 1-propenyl group and high selectivity of isomerization of allyloxyalcohol to cyclic acetal.     

Uranyl Schiff base complexes as new heterogeneous catalysts for halogen exchange reactions between alkyl halides and elemental halogens

Mild and effective procedure for the halogen exchange reaction of alkyl halides with elemental iodine and bromine catalyzed with uranyl Schiff base complexes in various aprotic solvents was developed. Corresponding alkyl bromides and iodides were obtained with high yields within 20—70 min. The structures of the target products were confirmed by physical and spectroscopic data.     

Rhodium carbene complexes as hydrosilylation catalysts

The catalytic activity of various rhodium carbene complexes has been investigated. These complexes are active for the hydrosilylation of a wide variety of unsaturated organic molecules such as olefins, acetylenes and dienes. Their activity is comparable to other rhodium(I) complexes previously used as hydrosilylation catalysts. The yield of products is found to vary with catalyst, silane and organic substrate.     

Anchored palladium-tin complexes as telomerization catalysts

The telomerization of butadiene with diethylamine in the presence of palladium-tin complexes obtained through interaction between palladium -allyl compounds and tin acetate has been studied. Palladium-tin complexes are characterized by high activity and low solubility in the diethylamine-butadiene mixture. Very active supported telomerization catalysts with high palladium concentrations are obtained by means of anchoring palladium-tin complexes to an SiO₂ surface. , - . , -. SiO₂ .     

Silica-immobilised amine-platinum complexes as hydrosilylation catalysts

A simple method has been used to assess the efficiency of a variety of platinumamine compexes anchored to silica and anionic complexes supported on a silica-based ion-exchanger in the catalysis of the hydrosilylation of dec-1-ene by (Me₃SiO)₂Si(H)Me. In all cases, platinum was leached from the support, so that the catalyst became less active on each re-use. A rough correlation between extent of leaching and activity suggested that the effective catalysis was actually occurring homogeneously. The silane was responsible for the leaching.     

Nitrogen-containing carbon nanotubes as solid base catalysts

Nitrogen-containing carbon nanotubes (NCNT) are effective re-usable solid base catalysts, their activity for a Knoevenagel condensation being related to the amount of pyridinic nitrogen incorporated in the NCNT structure, which could be tuned by the synthesis parameters of the catalyst.     

Tetrapyrrole bizirconium complexes as active catalysts for ethylene polymerization

Ethylene polymerization was carried out by using a group of new dizirconium(IV) tetrapyrrole complexes as catalysts and MAO as co-catalyst under 1 atmosphere pressure of ethylene gas at 25 and 40°C. The highest value of catalyst activity was obtained at 40°C by using bizirconium complexes including one calix[4]pyrrole between two zirconium centers and two terminal chlorines, while zirconium(IV) complexes with coordinated THF, almost have not catalytic activity. The maximum catalytic activity mounted to 830 kg/mol·bar·h by Zr₂(Cy₄ Pyr ₄)Cl₄. The results show that the structure of the coordination sphere of zirconium(IV) has great influence on the rate of polymerization, molar masses of forming polymer, and its molecular mass distribution. Correspondence: Sajjad Mohebbi, Chemistry Department, University of Kurdistan, P.O. Box 66176-416, Sanandaj, Iran.