Ti(O-i-Pr)4-NaNp-N2固氮体系在PtCl2(PPh3)2存在下和H2的反应

1975年Chatt等采用质子酸对稳定的钼钨分子氮络合物进行还原质子化反应,取得了生成氨的结果.我们在1979年开展了过渡金属氢化物与稳定和不稳定的分子氮络合物反应的研究,同样也取得了生成氨的结果.这个结果为在温和条件下H_2和配位氮分子氢化反应制取氨准备了实验基础.采用的稳定分子氮络合物有[Mo(N_2)_2(dppe)_2](Ⅰ),trans-[Mo(N_2)_2(PMePh_2)_4](Ⅱ);不稳定固氮体系有[Ti(O-i-Pr)_4-NaNp-N_2]     

二氧化碳的过渡金属络合物及其反应

前言形成过渡金属络合物是活化惰性分子最有效和最普遍的方法之一。络合的结果,改变了配位体的反应活性,创造了有利的反应空间条件,从而使我们能够实现在过渡金属络合物影响下的许多催化反应。有两个重要的生物过程:光合作用和固氮,长久以来就引起化学工作者的注意。大气中的分子氮(N_2)——通过生物固氮或工业合成氨——是地球上合成含氮化合物的唯一来源;而二氧化碳(CO_2)则是所有有生命物质的唯一碳源。因此,光合作用和生物固氮是地球上提供生命的两大过程。化学工作者正在努力创造类似的纯化学过程来模拟生物固氮和光合作用。近十年来,N_2与过渡金属化合物的反应已进行了广泛的研究。自从十年前 Allen 和 Senoff 制备了第一个分子氮络合物以来,到目前已成功地合成了一百多个过渡金属分子氮络合物。另一方面,N_2可以在温和条件下,在过渡金属化合物存在下还原,水解之后产生氨或肼。但是,现在的化学固氮体系,在固氮效果方面还远不能与固氮酶相比。迄今,对生物固氮的还原机理尚在研究中。最近,Chatt 报导,单金属络合的分子氮络合物[M(N_2)_2(PR_3)_4](M=Mo 或 W;R=烷基或芳基),在质子环境中,温和条件下,以高达90%的产率还原为 NH_3。这一反应对于我们了解固     

VCl2(PPh3)2甲醇溶液光还原氮和放氢反应动力学及氮还原氢化机理的探讨

进行了VCl_2(PPh_3)_2甲醇溶液光还原氮和放氢反应动力学的研究,提出了肼是氮还原为氨的中间物的动力学证据。说明Ⅴ(Ⅱ)络合物是活性物种。氮分子的光还原氢化反应的可能机理是:以形成线形桥式双核钒(Ⅱ)的双氮基络合物活化,受氢原子攻击,形成配位的二亚胺和游离的肼,肼再还原质子化变成氨。     

关于VFeS原子簇化学研究的一点建议

在圆褐固氮菌中除了含有 Mo 酶外,另外还含有一种钒酶,钒固氮酶在缺钼条件下可进行 N_2的活化,而且可能含有同钼酶相似的活性中心。在 Fe_4S_4~*簇骼结构中,如果用一个钒原子置换 Fe_4S~*中的一个铁原     

双核过渡金属络合物引发氮分子活化研究

将自然界资源丰富但化学性质上极其惰性的氮气分子在温和条件下转化为氨及其他含氮化合物,具有非常重要的意义。过渡金属络合物引发氮分子的活化及官能化已成为现代工业固氮的一大研究热点。本文回顾了氮分子与双核过渡金属络合物结合的键型模式,总结了影响氮分子活化的诸多因素如配体调变效应、金属调变效应等,对双核过渡金属络合物引发的双氮裂解、双氮官能化及CO/CO2协助双氮活化官能化等反应的实验与理论研究现状和进展进行了简要综述,并对未来过渡金属络合物在氮分子固定的应用发展作了展望。     

硫氰氧钼(V)在不同离子强度溶液中稳定性的研究

钼氧基离子MoO3+中Mo为+5价,其外层电子结构为4d15s°,属d4s°杂化轨道,故MoO3+与硫氰根离子SCN-之间可能会发生如下络合反应,生成三种硫氰氧钼(V)络合物本文用分光光度法及一系列数学处理方法进行了研究,结果表明在本实验条件下,MoO3+与SCN-间确有络合反应发生,且求出络合物硫氰氧钼(V)在295K不同离子强度的二甲基亚砜-水介质中的各级积累稳定常数[1],进而求出其热力学各级积累稳定常数[2].     

固相配位化学反应研究(XLIX)——[(n-Bu)_4N]_3[Mo_4S_4Cl_4]的固相合成和晶体结构

近处来,有关环状四核钼硫化合物的报道很多,这些同核钼硫化合物都是通过改变反应溶液的酸碱度和变换不同的有机配体或无机配体产生的,与之有关的固体合成尚未见文献报道.我们在探索低加热温度(100℃左右)下的配位化合物的固相反应过程中,已合成出了几十种新的同核或异核的Mo(W)-S化合物(包括含20种金属原子的大核簇合物[(n-Bu)_4N]_4[Mo_8Cu_(12)S_(32)]~[9]).标题化合物也是其中之一.本文将报道它的固相合成及晶体结构.     

草酸双过氧钒配合物与有机配体相互作用的NMR和ESI－MS研究

应用~1H, ~(13)C和~(51)V多核NMR技术和电喷雾质谱等谱学手段研究草酸双过 氧钒配合物与吡啶、4－甲基咪唑、咪唑等有机配体的相互作用。研究发现：这些 相互作用都生成过氧钒物种[OV(O_2)_2L]~-（L为有机配体），其从易到难的顺序 为咪唑＞4－甲基咪唑＞吡啶。当配体为4－甲基咪唑时，产物是一对未见报道的异 构体。研究结果表明：将NMR技术和电喷雾质谱有机结合是研究此类体系切实可行 的方法，有助于提示钒化合物与有机配体相互作用的规律和机制。     

链状三核钼(钨)硫原子簇化合物[M_3O_2S_8]~(2-)的合成、光谱和晶体结构

本文以[NH_4]_2MO_nS_(4-n)(M=Mo、W,n=0-2)为原料,在酸性和中性条件下,合成出九个新的三核不对称钼硫和钨硫原子簇状化合物L_2[M_3O_2S_8][L=(n-Bu)_4N、Ph_4P、PyC_(16)H_(33)、(CH_3)_3NC_(16)H_(33)、Et_4N]。用元素分析、红外光谱、紫外光谱对簇合物进行了表征,并测定了其中 [(n-Bu)_4N]_2[Mo_3O_2S_8](1)和[(n-Bu)_4N]_2[W_3O_2S_8](5)两个簇合物的晶体结构,簇合物1和5均属单斜晶系,P2_1/c空间群,簇合物1的晶胞参数:a=15.910(2),b=15.411(1),c=20.407(5)A,β=103.40°(1),V=4867.5A~3,Z=4,最终偏离因子R=0.060。簇合物5的晶胞参数。a=15.896(4),b=15.674(2),c=20.409(9)A,β=103.43°(3),V=4946.5A~3,Z=4,最终偏离因子为R=0.051。本文又一次验证了钼(钨)硫成簇反应是分子内部电子转移反应,并提出了可能的成簇反应历程。     

固氮酶催化活性中心及其化学模拟

固氮酶是固氮微生物在常温常压下固氮成氨的催化剂,其催化机理和化学模拟一直是国际上长期致力研究的对象.钼铁蛋白高分辨1.0单晶X射线衍射分析表明,固氮酶催化活性中心铁钼辅基的结构为Mo Fe7S9C(R-homocit),其中,Mo原子和3个u2-硫配体、1个组氨酸和1个高柠檬酸配位,形成八面体构型.高柠檬酸以α-烷氧基氧和α-羧基氧与钼螯合形成双齿配位,氨基酸残基上的组氨酸咪唑氮和半胱氨酸巯基与钼和铁单齿配位.在固氮酶铁钼辅基的生物合成过程中,高柠檬酸和咪唑侧基是在最后的合成步骤插入铁硫碳簇前驱体中,其中高柠檬酸和咪唑侧基有可能对质子传递以及稳定Mo Fe7S9C簇起到重要作用.本文从固氮酶铁钼辅基结构出发,结合最近本课题组从化学模拟出发,将固氮酶催化活性中心铁钼辅基结构修订为加氢新结构Mo Fe7S9C(R-Hhomocit)的研究,着重介绍了近年来国内外固氮酶活性中心、生物合成和催化作用机理的研究进展,并展望了固氮酶的研究前景.     

电羧化苯乙烯基苯基酮合成2,4-二苯基-4-丁酮酸

研究了常压下以CO2和苯乙烯基苯基酮为原料的电羧化反应. 在一室型电解池中, 用Mg作为辅助电极, 不锈钢、铜、镍、钛、石墨电极等作为工作电极, Ag/AgI为参比电极, 恒电位电解苯乙烯基苯基酮和CO2可得到产物2,4-二苯基-4-丁酮酸. 为提高电解产率, 优化了电解条件, 对影响该反应的溶剂、支持盐、阴极材料、电解电位、底物浓度和温度等因素作了进一步讨论. 实验结果表明, 不同的电解条件下, 苯乙烯基苯基酮的还原性能存在较大差异. 通过变化规律的研究, 找到了各个影响因素的最佳条件为: 反应温度为0 ℃, MeCN作为溶剂, 0.1 mol•L－1 四乙基四氟硼酸铵为支持盐, 不锈钢电极为工作电极, Mg棒为辅助电极, 电解电位是－1.75 V. 在此条件下恒电位电解, 2,4-二苯基-4-丁酮酸的产率可达88%. 在乙腈中还研究了苯乙烯基苯基酮的电化学行为, 推测其电羧化反应经历一个电子传递反应-化学反应-电子传递反应-化学反应(ECEC)过程.     

Electrochemical Reduction of Trichlorobiphenyls: Mechanism and Regioselectivity

The regioselectivity of electrochemical reduction of four trichlorobiphenyls (PCB 28–30 and PCB 37) was studied by cyclic voltammetry and bulk electrolysis. The number of stages and mechanism of electrochemical reduction of each of the examined substrate were inferred on the basis of the experimental electron transfer coefficients and calculated (DFT) bond lengths and potential energy surface sections. GC/MS analysis of the controlled potential electrolysis products showed that chlorine atom in the disubstituted ring of trichlorobiphenyls is reduced more readily than in the monosubstituted ring and that the rate of chlorine reduction changes in the series o-Cl > p-Cl > m-Cl.     

Catalytic Reduction of Bisulfite by Myoglobin/Surfactant Films

The voltammetry of bisulfite at a film formed with myoglobin was studied in aqueous solutions. A broad wave was observed for the reduction of bisulfite. Using controlled potential electrolysis, the reduction at potentials positive of the Fe^II/Fe^I wave formed dithionite exclusively. As the potential approached the region for the Fe^II/Fe^I reduction, bisulfite was reduced primarily to HS⁻. Even at the negative potentials, some dithionite was still formed, which could then be electrochemically reduced to thiosulfate. Analysis of the formation of HS⁻, dithionite and thiosulfate during the electrolysis was consistent with the parallel formation of HS⁻ and dithionite, the latter of which was reduced to thiosulfate. Thiosulfate was verified by chemical analysis of the products from controlled potential electrolysis of the solution, and dithionite was observed spectroscopically using spectroelectro−chemistry.     

LiCl-KCl-LaCl3熔盐体系中La(III)的电化学行为

在773 K条件下,研究了La（III）在LiCl-KCl熔盐中W和Ni电极上的电化学行为。La（III）还原反应是一步三电子转移的准可逆反应;通过在Ni电极上直接电沉积La的方法可以获得La-Ni金属间化合物;恒电位电解可以获得含三种金属间化合物（LaNi₅、La₇Ni₁₆和La₂Ni₃）的La-Ni合金层,并且通过X射线衍射仪（XRD）和扫描电镜-能谱分析仪（SEM-EDS）确定物相并表征结构。采用开路计时电位法估算了LaNi₅金属间化合物的标准生成吉布斯自由能。揭示了恒电位电解方法是制备La-Ni镀层合金以及提取熔盐中La的有效方法。     

Polarographic reduction of some mesoionic 2,3-diaryl-2 H-tetrazolium-5-thiolate compounds

The polarographic behaviour at the DME of 2,3-diphenyl-, 2,3-di(4-methylphenyl)- 2,3-di(3-chlorophenyl- and 2,3-di(2-chlorophenyl)-2 H-tetrazolium-5-thiolate compounds was investigated in 10% (v/v) aqueous methanol over a wide range of pH. The reduction proceeded through one four-electron irreversible wave to give the corresponding thiocarbazide. A mechanism for this reduction was proposed and subsequently substantiated by a controlled potential electrolysis of a mesoionic compound whereby the identify of the final reduction product has been proved spectrophotometrically to be the thiocarbazide.     

Electrochemical oxidation of 2-thiouracil at pyrolytic graphite electrode

2-Thiouracil has been studied in phosphate buffers of pH 1.95-11.08 using linear and cyclic sweep voltammetry, coulometry, controlled potential electrolysis and spectral studies. One well-defined oxidation peak I(a) in the pH range 1.95-11.08 was noticed. The number of electrons involved in peak I(a) was found to be four in a thin layer cell whereas under exhaustive electrolysis condition oxidation was found to involve six electrons. A reduction peak II(c) (2e, 2H(+)) is noticed in the reverse sweep. Spectral studies during oxidation were carried out at different pH. Kinetic studies indicated that the decay of the UV-absorbing intermediate is a first order reaction. The products of the electrooxidation have been characterized and a tentative EC mechanism has been suggested for the oxidation of 2-thiouracil.     

Analysis of active chemical species generated by electrolysis using non-aqueous capillary electrophoresis. Detection of the anion radical and the divalent anion of tetracyanoquinodimethane

We have investigated detection of the anion radical and the divalent anion of tetracyanoquinodimethane (TCNQ) by acetonitrile-CE under anaerobic conditions. With electrolysis at a potential of 0.0 V (vs. Ag/AgCl), an acetonitrile solution of TCNQ turned green, characteristic of the TCNQ anion radical (TCNQ-). Only one peak of the anionic compound was observed in CE of the electrolysis solution and it should be that of TCNQ-. Then, the electrolysis potential was shifted to -0.8 V expected to be sufficient potential for the further reduction of TCNQ-, and the solution turned almost colourless. In CE analysis of the latter solution, another anionic component possessing a larger electrophoretic mobility than that of TCNQ- was detected, and it was decomposed immediately under aerobic conditions. This product was strongly suggested to be the divalent anion of TCNQ, and the present method would contribute notably to detection of the unstable species.     

Electrochemical reduction of triorganohalo-silanes and -germanes

The electrochemical reduction of triorganohalo-silanes and -germanes in 1,2-dimethoxyethane has been investigated by polarography, cyclic voltammetry, controlled potential coulometry, and macroscale electrolysis. The reduction of the silicon compounds exhibits a single irreversible wave. The polarograms for the germanium compounds exhibit two irreversible waves. The second wave shifts to more anodic potentials with addition of phenol or acetic acid. Dimer (i.e. disilanes or digermanes) are the main product of macroscale electrolysis in aprotic solvent but the hydrides are the principal products in protic solution.The results are interpreted in terms of the coexistence of two separate processes. The first involves a one electron reduction followed by dimerization of the radical. At higher cathodic potential a two electron charge transfer step occurs to form an anion, which in aprotic solvents reacts with the starting halogeno compound to form dimer, and in protic solutions gives the hydride.     

氯化物熔盐中钕离子在铂电极上的电化学还原

利用极谱,Ⅲ利用电位阶跃研究了轻稀土离子在碱金属氯化物熔盐中的阴极还原。本文作者研究过Sm~(3 )在NaCl-KCl熔盐中的电还原。上述工作分别提出了稀土离子一步还原和分步还原的结论。本文采用线性扫描伏安法和恒电位电解,并配以扫描电子显微镜X射线能谱分析,对Nd~(3 )在Pt电极上的阴极还原过程进行了研究,利     

Ion transfer of bromophenol blue across liquid-liquid interfaces

The ion transfer of the acidic dye bromophenol blue (BPB) at the interfaces of water/nitrobenzene (W/NB), water/1,2-dichloroethane (W/1,2-DCE) and water/(nitrobenzene+chlorobenzene) (W/(NB +CB)) was studied in detail by cyclic voltammetry (CV), chronopotentiometry with linear current scanning (CLC), controlled potential electrolysis and UV spectroscopic methods. Using controlled potential electrolysis, we observed successfully the transfer process of BPB across the W/NB interface from the colour changes of BPB in two different phases. The proposed transfer mechanism for BPB is proved to be reasonable using UV spectroscopy of the product of the electrolysis. The standard potential differences Δ^o_w^o and the standard Gibbs energies of the BPB transfer from water to some organic solvents were calculated. The dissociation constants of BPB obtained were quite close to the literature values.