Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.     

Arylation with Unsymmetrical Diaryliodonium Salts: A Chemoselectivity Study

Phenols, anilines, and malonates have been arylated under metal‐free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti‐ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal‐free reagents.     

Investigation of Functionalized α‐Chloroalkyllithiums for a Stereospecific Reagent‐Controlled Homologation Approach to the Analgesic Alkaloid (−)‐Epibatidine

Four putative functionalized α‐chloroakyllithiums RCH₂CHLiCl, where R=CHCH₂ ( 18 a ), CCH ( 18 b ), CH₂OBn ( 18 c ), and CH[O(CH₂)₂O] ( 18 d ), were generated in situ by sulfoxide–lithium exchange from α‐chlorosulfoxides, and investigated for the stereospecific reagent‐controlled homologation (StReCH) of phenethyl and 2‐chloropyrid‐5‐yl ( 17 ) pinacol boronic esters. Deuterium labeling experiments revealed that α‐chloroalkyllithiums are quenched by proton transfer from their α‐chlorosulfoxide precursors and it was established that this effect compromises the yield of StReCH reactions. Use of α‐deuterated α‐chlorosulfoxides was discovered to ameliorate the problem by retarding the rate of acid‐base chemistry between the carbenoid and its precursor. Carbenoids 18 a and 18 b showed poor StReCH efficacy, particularly the propargyl group bearing carbenoid 18 b , the instability of which was attributed to a facile 1,2‐hydride shift. By contrast, 18 d , a carbenoid that benefits from a stabilizing interaction between O and Li atoms gave good StReCH yields. Boronate 17 was chain extended by carbenoids 18 a , 18 b , and 18 d in 16, 0, and 68 % yield, respectively; α‐deuterated isotopomers D ‐ 18 a and D ‐ 18 d gave yields of 33 and 79 % for the same reaction. Double StReCH of 17 was pursued to target contiguous stereodiads appropriate for the total synthesis of (?)‐epibatidine ( 15 ). One‐pot double StReCH of boronate 17 by two exposures to (S)‐D ‐ 18 a (≤66 % ee), followed by work‐up with KOOH, gave the expected stereodiad product in 16 % yield (d.r.～67:33). The comparable reaction using two exposures to (S)‐D ‐ 18 d (≤90 % ee) delivered the expected bisacetal containing stereodiad (R,R)‐DD ‐ 48 in 40 % yield (≥98 % ee, d.r.=85:15). Double StReCH of 17 using (S)‐D ‐ 18 d (≤90 % ee) followed by (R)‐D ‐ 18 d (≤90 % ee) likewise gave (R,S)‐DD ‐ 48 in 49 % yield (≥97 % ee, d.r.=79:21). (R,S)‐DD ‐ 48 was converted to a dideuterated isotopomer of a synthetic intermediate in Corey’s synthesis of 15 .     

[Pd(Fmes)2(tmeda)]: A Case of Intermittent C?H⋅⋅⋅F?C Hydrogen‐Bond Interaction in Solution

The X‐ray structure of the title compound [Pd(Fmes)₂(tmeda)] (Fmes=2,4,6‐tris(trifluoromethyl)phenyl; tmeda=N,N,N′,N′‐tetramethylethylenediamine) shows the existence of uncommon C? H???F? C hydrogen‐bond interactions between methyl groups of the TMEDA ligand and ortho‐CF₃ groups of the Fmes ligand. The ¹⁹F NMR spectra in CD₂Cl₂ at very low temperature (157 K) detect restricted rotation for the two ortho‐CF₃ groups involved in hydrogen bonding, which might suggest that the hydrogen bond is responsible for this hindrance to rotation. However, a theoretical study of the hydrogen‐bond energy shows that it is too weak (about 7 kJ mol^?1) to account for the rotational barrier observed (ΔH^≠=26.8 kJ mol^?1), and it is the steric hindrance associated with the puckering of the TMEDA ligand that should be held responsible for most of the rotational barrier. At higher temperatures the rotation becomes fast, which requires that the hydrogen bond is continuously being split up and restored and exists only intermittently, following the pulse of the conformational changes of TMEDA.     

Unzipping Nucleoside Channels by Means of Alcohol Disassembly

Gold nanoparticles capped with simple adenosine derivatives can form colloidal aggregates in nonpolar solvents. Theoretical calculations indicate the formation of organic channels by the supramolecular assembly of the nanoparticles by means of hydrogen bonds between the adenine moieties. The aggregates were only negligibly sensitive to nPrOH, iPrOH, and tBuOH, whereas some showed a similar response to MeOH and EtOH, and others showed high selectivity toward MeOH. DNA nucleoside derivatives (1‐(2‐deoxy‐β‐D ‐ribofuranosyl)‐5‐methyluracil and 2′,3′‐O‐isopropylideneadenosine) as well as thymine and other aromatic compounds such as pyrene derivatives (pyrene, 1‐chloropyrene, 1‐hydroxypyrene, (1‐pyrenyl)methanol, and 2‐hydroxynapthalene) did not induce disassembly of the nanoparticle aggregates. Data suggest that the nucleoside channels allow access to alcohols according to their size, and an efficient interaction between the alcohol and the adenine units destabilizes the hydrogen bonds, which eventually leads to nanoparticle disassembly.     

基于自交联杂萘联苯聚芳醚阴离子交换膜制备及其物理化学性质

以氯甲基杂环聚醚酮(CMPPEK)为原料,加入三乙胺进行铵化,并分别加入二乙烯三胺(DETA)和二乙胺(DEA),生成的仲胺基(或叔胺基)与邻近分子链氯甲基团进行自交联.经过制膜和离子交换反应,制备了DETA自交联杂萘联苯聚芳醚阴离子交换膜(DETA-QPPEK-OH)和DEA自交联杂萘联苯聚芳醚阴离子交换膜(DEA-QPPEK-OH).采用傅里叶变换红外(FTIR)光谱对制备自交联膜的化学结构进行表征.研究了DETA-QPPEK-OH和DEA-QPPEK-OH膜的理化性质,结果表明前者具有较低吸水率和更低溶胀度.通过研究DETAQPPEK-OH和DEA-QPPEK-OH膜的离子传导率随温度的变化规律,结果表明在80°C时其离子传导率分别达到0.060和0.028 S cm-1,表明本文制备的自交联膜具有较高离子传导率.此外还通过热重分析(TGA)对两类自交联膜的热稳定性进行了研究.     

钪元素对AB2型合金Zr1-xScxMn0.6V0.2Ni1.2Co0.1（x=0～1）储氢和电化学性能的影响

用真空电弧熔炼方法制备了Zr1-xScxMn0.6V0.2Ni1.2Co0.1(x=0～1)AB2型储氢合金,研究了Sc元素替代Zr对合金的微观组织结构、气态储氢及电化学性能的影响。研究结果表明,Zr1-xScxMn0.6V0.2Ni1.2Co0.1合金主要是由FCC型C15相、CsCl型结构的(ScZr)Ni相和少量的Ni10Zr7相组成,随Sc含量的增加,C15相丰度逐渐减小,(ScZr)Ni相丰度逐渐增加,当x=0.2时Ni10Zr7相基本消失;Sc元素对合金的首次气态吸氢动力学行为影响较大,随Sc含量的增加,合金吸氢动力学性能逐渐变缓,但吸氢容量逐渐提高,直至达x=1.0时的最大吸氢量1.87%;Sc元素对合金吸氢PCT曲线平衡氢压的影响规律不明显,随Sc含量增加,合金氢化物的形成焓ΔH从-26.66 kJ.mol-1逐渐减小到-8.14 kJ.mol-1。Sc元素的加入可明显改善合金电极的活化性能,提高放电容量,随Sc含量的增加,合金电极最大放电容量从x=0时的350.3 mAh.g-1增加到x=1时的429.8 mAh.g-1,呈先减小后增大的趋势,但电极容量的保持率S100随Sc含量增加而快速下降。     

Pt 含量对Co@Pt/C核壳结构催化剂性能的影响

采用两步还原法制得Co@Pt/C核壳结构催化剂, 其中Co与Pt 的总质量分数为20%. 通过改变金属前驱体的用量, 制备了不同Co:Pt 原子比的Co@Pt/C 催化剂, 以20% (w) Co@Pt(1:1)/C 与20% (w) Co@Pt(1:3)/C 表示. 采用透射电镜(TEM)、光电子射线能谱分析(XPS)、循环伏安(CV)、线性扫描伏安(LSV)等方法考察了其结构与性能, 并与实验室早先制备的40% (w) Co@Pt/C 催化剂进行了比较. 自制20% Co@Pt(1:1)/C 与20% Co@Pt(1:3)/C 催化剂的金属颗粒直径约为2.2-2.3 nm, 在碳载体上分散均匀, 粒径分布范围较窄, 电化学活性比表面积(ECSA)分别为56 和60 m²·g^-1, 均超过商用催化剂20% Pt/C(E-tek) (ECSA=54 m²·g^-1). 20%Co@Pt(1:1)/C 与20% Co@Pt(1:3)/C 的半波电位相较于40% Co@Pt(1:1)/C 和40% Co@Pt(1:3)/C 均向正向移动, 表现出更好的氧还原(ORR)催化活性, 并有望降低催化剂的成本, 在质子交换膜燃料电池领域表现出良好的应用前景.     

18O同位素标记定量肽段串联体蛋白质结合同位素稀释-多反应监测质谱的蛋白质绝对定量新方法

建立了定量肽段串联体蛋白质(concatamers of Q peptides, QconCATs)结合¹⁸O同位素标记-多反应监测质谱的蛋白质绝对定量新方法。首先对QconCAT重组蛋白质进行了纯度表征,十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)表征结果表明重组蛋白质的纯度在99%以上,相对分子质量约为63.4 kDa。对QconCAT重组蛋白质酶切后的肽段混合物进行质谱分析,并经pFind和pLabel软件处理,验证了目标肽段。还考察了QconCAT重组蛋白质的酶切效率和¹⁸O标记效率,并对QconCAT蛋白质结合¹⁸O标记-同位素稀释-多反应监测质谱方法进行了评价。实验结果表明,采用该方法对腾冲嗜热厌氧菌(Thermoanaerobacter tengcongensis, TTE)中选定蛋白质的肽段进行绝对含量测定时,相对标准偏差小于20%,准确度较高,说明该方法可用于复杂生物样本中蛋白质的绝对定量。更重要的是所建方法不仅解决了细胞培养氨基酸稳定同位素标记(SILAC)技术的重标试剂价格昂贵的问题,也为定量蛋白质组学提供了一种新的方法。     

结构稳定的CuO/TiO2纳米管的功能化溶胶修饰法制备及其催化CO氧化性能研究

以水热处理方法得到的钛酸纳米管为载体,采用含有醋酸铜的功能化钛溶胶对其进行一步浸渍修饰,制备结构稳定的CuO修饰TiO₂纳米管催化剂(CuO/TiO₂NTs)。通过XRD(X-射线衍射)、TEM(透射电子显微镜)、HR-TEM(高倍透射电子显微镜)、XPS(X-射线光电子能谱)、BET(氮气吸附-脱附法)、TPD(程序升温脱附法)等表征材料的结构和性质,并研究其催化CO氧化的性能。研究表明：经过溶胶浸渍处理过程,不仅将功能化铜组分负载在纳米管上,而且纳米管载体的耐热性能明显提高;催化剂载体、铜钛原子比及焙烧温度对催化剂的活性有明显影响,且400℃焙烧的Cu/Ti原子比为1∶5的CuO/TiO₂NTs的活性最高。