Study on the alkylation reaction of guanine and N-acetylguanine and the synthesis of 1''''-C alkylated carba-DHPG analogues

The alkylation reaction of guanine and N-acetylguanine with model compounds such as isopropyl bromide or 4-heptyl tosylate were studied. The reaction conditions such as temperature, solvent, base, and catalyst were examined for their effects on the reaction rate, and the yield and regioselectivity of the coupling reaction. The highest yield was obtained by using DMSO as the solvent. The reaction proceeded in a homogenous manner to give higher yield of 9-N and 7-N substituted product in a mole ratio of 1:1. The ratio could be raised to 2:1 if dibenzo-18-crown-6 was used as a catalyst. Using the above procedure, three carba-DHPG analogues bearing different 1'-C alkyl side chains were synthesized.     

Effects of pretreatment and reduction on the Co/Al2O3 catalyst for CO hydrogenation

The purpose of this study was to investigate the effect of preadsorbed CO at different temperatures, calcination temperatures, the combined influence of reduction temperature and time, and pretreatment using hydrogen or syngas as reduction agents on the F-T synthesis （FTS） activity and selectivity of Co/Al2O3 catalyst. The reactivity of the carbon species at higher preadsorption temperature with H2 in TPSR decreased, whereas the carbon-containing species showed higher reactivity over Co/Al2O3 catalyst with low calcination temperature. This agreed well with the order of catalytic activity for F-T synthesis on this catalyst. The catalytic activity of the catalyst varied with reduction temperature and time remarkably. CODEX optimization gave an optimum reduction temperature of 756 K and reduction time of 6.2 h and estimated C5＋ yield perfectly. The pretreatment of Co/Al2O3 catalyst with different reduction agents （hydrogen or syngas） showed important influences on the catalytic performance. A high CO conversion and C5＋ yield were obtained on the catalyst reduced by hydrogen, whereas methane selectivity on the catalyst reduced by syngas was much higher than that on the catalyst reduced by hydrogen.     

Synergistic Effects of the ZnCl2-SiCl4 Modified TiCl4 /MgCl2 /THF Catalytic System on Ethylene/1-Hexene and Ethylene/1-Octene Copolymerizations简

The copolymerizations of ethylene with 1-hexene or 1-octene by using TiCl4 /MgCl2 /THF catalysts modified with different metal halide additives(ZnCl2, SiCl4, and the combined ZnCl2-SiCl4) were investigated based on catalytic activity and copolymer properties. It was found that the catalyst modified with mixed ZnCl2-SiCl4 revealed the highest activities for both ethylene/1-hexene and ethylene/1-octene copolymerization. The increase in activities was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Based on the FTIR measurements, the characteristic C―O―C peaks of the catalysts modified with metal halide additives were slightly shifted to lower wavenumber when compared to the unmodified catalyst. This showed that the modified catalysts could generate more acid sites in the TiCl4 /MgCl2 /THF catalytic system leading to an increase in activities as well as comonomer insertion(as proven by13C-NMR). However, Lewis acidmodifications did not affect the microstructure of the copolymers obtained. By comparison on the properties of copolymers prepared with the unmodified catalyst, it was found that polymers with ZnCl2 and/or SiCl4 modification exhibited a slight decrease in melting temperature, crystallinity and density. It is suggested that these results were obtained based on the different amount of α-olefins insertion, regardless of the types of Lewis acids and comonomer.     

THERMAL DECOMPOSITION OF THE[Fe_6C(CO)_(16)]~(2-) ON ALUMINA AND MODIFIED ALUMINA

Thermal decomposition of the supported carbido cluster was investi-gated by in situ FT-IR spectroscopy in a temperature range of 25-300℃. Thesupported clusters on alumina and modified alumina with Me_4NBr or PPNClshow quite different decomposition ways in vacuo and under various atmo-spheres, such as H_2, CO, N_2 and CO + H_2. The different decomposition waysprobably lead to the different metal sites of the final catalyst.     

Methanol conversion to DME as a blue fuel:The beneficial use of ultrasonic irradiation for the preparation of CuO/H-MOR nanocatalyst

Methanol conversion to DME was investigated over CuO /H-MOR nanocatalyst prepared by precipitation and /or by precipitation flowed by ultrasonic irradiation methods. BET,XRD,SEM,NH3-TPD and H2-TPR techniques were used to characterize nanocatalysts. The effective ultrasonication factors encountered during carrying out the dehydration of methanol on Cuo /H-MOR zeolite catalysts to produce dimethylether are studied in the present work. These factors include: the type of ultrasonication media,the ultrasonication time,and the fixed weight of the solid catalyst per the volume of the ultrasonication liquid media( Wcatalyst/ Vliquidratio). XRD showed that structure of H-MOR is not damaged even after it is loaded with CuO nanoparticles or with ultrasonication. H2-TPR profiles indicated that reducibility of sonicated CuO / H-MOR nanocatalyst is higher than non-sonicated catalyst. It is found that employing ultrasound energy for 60 min has the highest influence on the surface properties of nanocatalyst and its catalytic performance( activity and stability) of CuO / H-MOR catalyst. Surface morphology( SEM) of the sonicated CuO /H-MOR catalysts have clarified that methanol by itself used as an ultrasonication medium gives the best results concerning the homogeneity of particle sizes compared to the non-sonicated catalyst,where large agglomerates and non-homogeneous clusters appeared. Water used as a sonication medium showed many large agglomerates in addition to some smaller particles resulted in lowcatalytic activity. The different alcohols and( Wcatalyst/ Vliquid) ratio were examined to give precise correlation with the catalytic activity of the sonicated CuO / H-MOR zeolite catalyst. These findings certified that ultrasonication has a deep effect on the surface morphology and hence on the catalytic behavior of the dehydration of methanol to DME. NH3-TPD shows that ultrasound irradiation has enhanced the acidity of CuO / H-MOR catalyst and hence it’s catalytic performance for DME formation.     

Amorphous Cu0 on Carbon Nanofiber as Recyclable Heterogeneous Catalyst for N-Arylation Reactions

A novel heterogeneous catalyst,amorphous Cu^0 on the carbon nanofibers was developed and characte-rized by means of several characterization techniques.The prepared Cu^0 was investigated as a heterogeneous catalyst for N-arylation reaction.The results show it is an excellent catalyst with recyclability,high consistency and catalytic activity.After the catalyst was used for 5 cycles in the N-arylation reaction,amorphous Cu^0 reunited into crystalline copper nanoparticles with different particle sizes and its good heterogeneity in the catalytic system was confirmed after the catalyst recovery.     

Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag／SiO2 Catalysts for CO Selective Oxidation in H2

The interactions of oxygen with pre~reduced silver catalysts as well as their catalytic propertiesfor CO selective oxidation in H2 after oxygen pre-treatment are studied in this paper. It is found that the pretreatment exerts a strong influence on the activity and selectivity of the silver catalyst. A drop in activity and selectivity is observed after treating a pre-reduced catalyst with oxygen at low temperatures,whereas a converse result is obtained after an oxidizing treatment at high temperatures (T≥350℃). O2-TPD results show that surface oxygen species adsorbs on silver surface after the oxygen treatment at low temperatures. However, penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile the surface oxygen species disappear. No other silver species except metallic silver are observed on all the catalysts by XRD, and the size of silver particle is not changed after the treatment with oxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also be removed by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorption and diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing the decrease in CO oxidation activity, in other words, it is important to obtain a clean silver surface for increasing the catalyst activity in CO removal from H2-rich feed gas. The differences in activity and selectivity due to the oxygen pretreatment at different temperatures axe discussed in terms of the changes in the surface/subsurface oxygen species of the silver particles.     

VINYLATION OF ARYL IODIDES CATALYZED BY〔POLY(STYRYL)BIPYRIDINE〕PALLADIUM(0)

[Poly(styryl)bipyridine]palladium(O),a polymer-bound hydrogrnation catalyst,was characterized by DRS,ESCA and electron microscopy.This material was used as cata-lyst for the vinylation of ary liodides.It was found that the catalytic activlty is comparableto that of the homogeneous catalyst and is not remarkably lowered on being used threetimes With this catalyst,a series of substituted stilbenes,cinnamic acids and methylcinnamates was prepared in high yields.     

EFFECT OF SUPPORT PORE STRUCTURE ON Pd-CATALYST ACTIVITY AND SELECTIVITY

The results from the tests in reaction temperature and space velocity suggest the reaction ofnitrite with CO is limited by pore diffusion resistance above 354 K.The effect of alumina and carbonsupports with different pore structure on the activity and selectivity of Pal-catalysts showed that thesupport with reasonable pore structure such as α-Al_2O_3 was favorable for the activity and selectivity ofthe catalyst.     

Facile and efficient synthesis of 2-substituted-Nl-carbethoxy-2,3-dihydro-4(1H)-quinazolinones in fluorous solvent

A facile,efficient and novel approach to access 2-substituted-N_1-carbethoxy-2,3-dihydro-4(1H)-quinazolinones was developed by condensation of substituted N-carbethoxyanthranilamide with alkyl,aromatic or heteroaromatic aldehydes in the refluxing 2,2,2- trifluoroethanol or hexafluoroisopropanol using p-toluenesulfonic acid as catalyst.     

Bioorganometallic fulvene-derived titanocene anti-cancer drugs

6-Substituted fulvenes are interesting and easily accessible starting materials for the synthesis of novel substituted titanocenes via reductive dimerisation, carbolithiation or hydridolithiation reactions, which are followed by a transmetallation reaction with titanium tetrachloride in the latter two cases. Depending on the substitution pattern, these titanocenes prove to be bioorganometallic anti-cancer drugs, which have significant potential against advanced or metastatic renal-cell cancer. Patients bearing these stages of kidney cancer have a poor prognosis so far and therefore real progress in the area of metal-based anti-cancer drugs may come from this simple and effective synthetic approach. This tutorial review provides an insight into the synthesis of fulvene-derived titanocenes and their activity in preclinical experiments.     

Further Studies on Homo- and Copolymerization of Styrene through Metallocenic Initiator Systems

Summary: Binary metallocene-MAO and ternary diphenylzinc-metallocene-MAO initiator systems have been tested as initiators in the homopolymerization of styrene and also in its copolymerization with several diverse comonomers including substituted styrenes, styrene derivatives, α-olefins and dienes. Various titanocenes and zirconocenes and some exploratory experiment with hafnocene were carried out. The results indicate that titanocenes were more effective than zirconocenes in the homopolymerization of styrene while zirconocenes did better in α-olefin polymerization. It was found that titanocenes generated mainly syndiotactic polystyrene, s-PS, while zirconocenes yielded atactic polystyrene or, depending on the zirconocene, a low percentage of s-PS. For these types of initiators the polymerization process depends largely on the inductive effect of the substituents linked to the benzene ring of styrene and on its position (ortho, meta or para). Substituent multiplicity reduced markedly the effectiveness of these initiator systems. Styrene/isoprene polymerization was also studied using binary zirconocene-MAO initiator systems that yielded low conversions and also low molecular weight polymers.     

大基团取代不对称茂钛（Ⅳ）化合物的合成

大基团取代不对称茂钛（Ⅳ）化合物的合成舒学军贺峥杰＊陈寿山（南开大学元素有机化学研究所天津３０００７１）关键词有机锂，富烯，茂钛化合物，合成１９９６－０６－１９收稿，１９９６－１２－３１修回国家自然科学基金资助课题取代茂钛化合物常常是烯烃异构化的良好...     

茂钛配合物—纳米氢化钠双组分高活性加氢催化剂的研究

提出了带有不同取代基的茂钛配合物与纳米氢化钠（ＮａＨ）组成的高活性加氢催化剂，在常温常压下，取代茂钛配合物ＴｉＣｌ２／ＮａＨ对１－己烯的加氢反应有极高的初始活性，ＴＯＦｍａｘ达到１１０ｍｏｌＨ２／（ｍｏｌＴｉ．ｓ），催化转换数达到２２２００ｍｏｌＨ２／（ｍｏｌＴｉ）。该催化体系对底物有明显的专一选择性，只有端烃才能发生加氢反应，且无民构化副反应发生，纳米氢化钠的助剂作用是该催化体系高活性关键因素。     

The synthesis and cytotoxic evaluation of a series of benzodioxole substituted titanocenes

Using 6‐benzo[1,3]dioxolefulvene ( 1a ), a series of benzodioxole substituted titanocenes was synthesized. The benzyl‐substituted titanocene bis[(benzo[1,3]dioxole)‐5‐methylcyclopentadienyl] titanium (IV) dichloride ( 2a ) was synthesized from the reaction of Super Hydride with 1a . An X‐ray determined crystal structure was obtained for 2a . The ansa‐titanocene {1,2‐di(cyclopentadienyl)‐1,2‐di‐(benzo[1,3]dioxole)‐ethanediyl} titanium(IV) dichloride ( 2b ) was synthesized by reductive dimerisation of 1a with titanium dichloride. The diarylmethyl substituted titanocene bis(di‐(benzo[1,3]dioxole)‐5‐methylcyclopentadienyl) titanium(IV) dichloride ( 2c ) was synthesized by reacting 1a with the para‐lithiated benzodioxole followed by transmetallation with titanium tetrachloride. When titanocenes 2a–c were tested against pig kidney (LLC‐PK) cells inhibitory concentrations (IC₅₀) of 2.8 × 10^?4, 1.6 × 10^?4 and 7.6 × 10^?5 M , respectively, were observed. These values represent improved cytotoxicity against LLC‐PK, when compared with unsubstituted titanocene dichloride, but are not as impressive as values obtained for titanocenes previously synthesized using the above methods. Copyright © 2006 John Wiley & Sons, Ltd.     

Binuclear titanium complexes coordinated by rigid p-phenylene linked bis-β-carbonylenamine: Synthesis,structure, ethylene polymerization and copolymerization with 1,5-hexadiene

Binuclear complexes for olefin polymerization have attracted great attention due to their unique catalytic properties compared with their mononuclear counterparts. Here a series of p-phenylene-bridgedbis-β-carbonylenamine ligands and their binuclear Ti complexes Ti ₂ L ¹ – Ti ₂ L ³ were prepared and characterized by ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy, and elemental analysis. The binuclear complex Ti ₂ L ³ bearing an octylthio sidearm was further investigated by single-crystalX-ray diffraction, which revealed that the ligand was of β-imino enol form, with one titanium atom ligated with six other atoms, forming a deformed octahedral configuration. Furthermore, the ligand in Ti ₂ L ³ adopted a cis configuration, which was different from the trans configuration of its m-phenylene-bridged derivatives. These binuclear complexes ( Ti ₂ L ¹ – Ti ₂ L ³ ) could catalyze ethylene polymerization and copolymerization with 1,5-hexadiene(1,5-HD) efficiently under modified methylaluminoxane activation. Compared with the mononuclear complex TiL ⁵ , the binuclear catalysts were thermally more stable and showed higher activity for ethylene polymerization at higher temperatures. The activity of these titanium complexes for the copolymerization of ethylene with 1,5-HD were over 10⁶ g/mol Ti.h.atm, almost twice as high as for homopolymerization. Compared with the mononuclear analogue TiL ⁵ and the m-substituted binuclear derivative Ti ₂ L ⁴ , binuclear catalyst Ti ₂ L ² showed higher activity and insertion rate of the comonomer. The activity of Ti ₂ L ² was two to three times higher than that of TiL ⁵ and Ti ₂ L ⁴ , indicating that p-substituted binuclear catalysts generate clear bimetallic synergistic effect for the copolymerization of ethylene and 1,5-HD. Meanwhile, 1,5-HD takes 1,3-cyclopentyl form in the polymer by 1,3-insertion. The copolymer prepared by binuclear catalysts had higher molecular weight and wider molecular weight distribution than that prepared by the mononuclear catalyst.     

钛开环夹心羰基化合物的构象分析

合成了３个钛开环夹心羰基化合物．用１ＨＮＭＲ方法对３个钛开环夹心羰基化合物进行了研究实验结果表明,钛开环夹心羰基化合物的分子构象与开环配体的取代状况有关．由对称取代戊稀基配体形成的化合物只有１种构象,由非对称取代戊二稀基［２ＣＨ３Ｃ５Ｈ６］－形成的化合物具有２种构象（ｃｉｓ和ｔｒａｎｓ）．     

Electrochemical Study of Highly Substituted Titanocene Dihalides

Titanocene dihalides are promising alternative to Cisplatin in cancer chemotherapy which should reduce negative side effects and overcome increasing resistance of cancer cells. Since the mechanism of anti‐cancer action is associated with generation of reactive oxygen species (ROS), hence with redox processes, electrochemical investigation of titanocene species would be an important issue, not applied up to now. In this article we report on the electrochemical reduction as well as oxidation of titanocene difluorides and dichlorides where unsubstituted as well as highly substituted titanocene dihalides are compared. The experiments were realized in acetonitrile using various electrode materials. The studied series was completed by a new dimethylsilylene bridged ansa‐titanocene difluoride which was characterized by NMR and x‐ray crystallography. The influence of structure and substitution on the redox properties was evaluated and, in addition to this, cytotoxicity of studied titanocene dihalides against human ovarian cancer cell lines A2780 and SK‐OV‐3, as well as against human embryonic kidney cell line HEK293 were screened. Two of highly substituted titanocenes exhibit cytotoxicity comparable with that of Cisplatin.     

Comparative study of metal-catalyzed iminations of sulfoxides and sulfides

A comparative study of the imination of sulfur compounds with various metal catalysts in combination with isolated or in situ generated iminoiodinanes (PhI==NR) as nitrogen sources is presented. The influence of the metal catalyst towards the imination of a variety of substituted sulfoxides has been evaluated. Moreover, the effect of the different oxidation states of sulfur on the reactivity and selectivity of the nitrogen transfer redox process in the formation of sulfilimines and sulfoximines was studied. Depending on both the specific metal catalyst as well as the employed nitrene precursor, the sulfide/sulfoxide imination ratio varied in transformations of thianthrene-5-oxide and substituted para-thio phenylsulfoxides.     

SYNTHESIS OF NOVEL THIOPHENEDIMETHYLENE BRIDGED HOMOBINUCLEAR METALLOCENES AND THEIR CATALYTIC PROPERTIES FOR ETHYLENE POLYMERIZATION

By treating disodium(thiophenedirnethylene)dicyclopentadienide C_4H_2S(CH_2C_5H_4Na)_2 with two equivalent of CpTiCl_3 or CpZrCl_3 DME at 0℃ in THF,two new thiophenedimethylene bridged binuclear metallocenes [Cl_2MC_5H_5][C_5H_4CH_2C_4H_2SCH_2C_5H_4][C_5H_5MCl_2](M=Ti 3,M=Zr 4)were synthesized in high yield and their structures were characterized by ~1H-NMR.These complexes were used as catalysts for ethylene polymerization in the presence of methylaluminoxane(MAO).The effects of polymerization temperature,time,concentration of catalyst,molar ratio of MAO/Cat on polymerization were studied in detail.The catalytic activities of thiophenedimethylene bridged binuclear metallocene catalysts(3,4)reached 2.44×10~5 g PE mol~(-1)·cat~(-1)·h~(-1),9.61×10~5 g PE mol~(-1)·cat~(-1)·h~(-1) respectively,which are higher than that of pheneyldimethylene bridged binuclear metallocene catalysts and much higher than that of corresponding mononuclear metallocenes(Cp_2TiCl_2 and Cp_2ZrCl_2).The molecular weight distribution curves of polyethylenes produced by binuclear metallocene catalysts(3,4)and by mononuclear metallocene catalyst have only single peak,but the former(MWD=3.5-4.7)is obviously broader than the latter(MWD=2.0-2.2).