Ancillary ligand effects : from zirconium(IV)-catalyzed homogeneous propylene polymerization to platinum(II)-mediated C-H bond activation

A series of C_s- and C₁-symmetric doubly-linked ansa-metallocenes of the general formula {1,1'-SiMe₂-2,2'-E-('ƞ⁵-C₅H₂-4-R¹)-(ƞ⁵-C₅H-3',5'-(CHMe₂)₂)}ZrC₂ (E = SiMe₂ (1), SiPh₂ (2), SiMe₂ -SiMe₂ (3); R¹ = H, CHMe₂, C₅H₉, C₆H₁₁, C₆H₅) has been prepared. When activated by methylaluminoxane, these are active propylene polymerization catalysts. 1 and 2 produce syndiotactic polypropylenes, and 3 produces isotactic polypropylenes. Site epimerization is the major pathway for stereoerror formation for 1 and 2. In addition, the polymer chain has slightly stronger steric interaction with the diphenylsilylene linker than with the dimethylsilylene linker. This results in more frequent site epimerization and reduced syndiospecificity for 2 compared to 1.

C₁-Symmetric ansa-zirconocenes [1,1 '-SiMe₂-(C₅H₄)-(3-R-C₅H₃)]ZrCl₂ (4), [1,1 '-SiMe₂-(C₅H₄)-(2,4-R₂-C₅H₂)]ZrCl₂ (5) and [1,1 '-SiMe₂-2,2 '-(SiMe₂-SiMe₂)-(C₅H₃)-( 4-R-C₅H₂)]ZrCl₂ (6) have been prepared to probe the origin of isospecificity in 3. While 4 and 3 produce polymers with similar isospecificity, 5 and 6 give mostly hemi-isotactic-like polymers. It is proposed that the facile site epimerization via an associative pathway allows rapid equilibration of the polymer chain between the isospecific and aspecific insertion sites. This results in more frequent insertion from the isospecific site, which has a lower kinetic barrier for chain propagation. On the other hand, site epimerization for 5 and 6 is slow. This leads to mostly alternating insertion from the isospecific and aspecific sites, and consequently, a hemi-isotactic-like polymers. In comparison, site epimerization is even slower for 3, but enchainment from the aspecific site has an extremely high kinetic barrier for monomer coordination. Therefore, enchainment occurs preferentially from the isospecific site to produce isotactic polymers.

A series of cationic complexes [(ArN=CR-CR=NAr)PtMe(L)]⁺[BF₄]⁺ (Ar = aryl; R = H, CH₃; L = water, trifluoroethanol) has been prepared. They react smoothly with benzene at approximately room temperature in trifluoroethanol solvent to yield methane and the corresponding phenyl Pt(II) cations, via Pt(IV)-methyl-phenyl-hydride intermediates. The reaction products of methyl-substituted benzenes suggest an inherent reactivity preference for aromatic over benzylic C-H bond activation, which can however be overridden by steric effects. For the reaction of benzene with cationic Pt(II) complexes, in which the diimine ligands bear 3,5-disubstituted aryl groups at the nitrogen atoms, the rate-determining step is C-H bond activation. For the more sterically crowded analogs with 2,6-dimethyl-substituted aryl groups, benzene coordination becomes rate-determining. The more electron-rich the ligand, as reflected by the CO stretching frequency in the IR spectrum of the corresponding cationic carbonyl complex, the faster the rate of C-H bond activation. This finding, however, does not reflect the actual C-H bond activation process, but rather reflects only the relative ease of solvent molecules displacing water molecules to initiate the reaction. That is, the change in rates is mostly due to a ground state effect. Several lines of evidence suggest that associative substitution pathways operate to get the hydrocarbon substrate into, and out of, the coordination sphere; i.e., that benzene substitution proceeds by a solvent- (TFE-) assisted associative pathway.

Theory of s-d exchange scattering in dilute magnetic alloys

The problem of s-d exchange scattering of conduction electrons off localized magnetic moments in dilute magnetic alloys is considered employing formal methods of quantum field theoretical scattering. It is shown that such a treatment not only allows for the first time, the inclusion of multiparticle intermediate states in single particle scattering equations but also results in extremely simple and straight forward mathematical analysis. These equations are proved to be exact in the thermodynamic limit. A self-consistent integral equation for electron self energy is derived and approximately solved. The ground state and physical parameters of dilute magnetic alloys are discussed in terms of the theoretical results. Within the approximation of single particle intermediate states our results reduce to earlier versions. The following additional features are found as a consequence of the inclusion of multiparticle intermediate states;

(i) A non analytic binding energy is pre sent for both, antiferromagnetic (J < o) and ferromagnetic (J > o) couplings of the electron plus impurity system.

(ii) The correct behavior of the energy difference of the conduction electron plus impurity system and the free electron system is found which is free of unphysical singularities present in earlier versions of the theories.

(iii) The ground state of the conduction electron plus impurity system is shown to be a many-body condensate state for J < o and J > o, both. However, a distinction is made between the usual terminology of "Singlet" and "Triplet" ground states and nature of our ground state.

(iv) It is shown that a long range ordering, leading to an ordering of the magnetic moments can result from a contact interaction such as the s-d exchange interaction.

(v) The explicit dependence of the excess specific heat of the Kondo systems is obtained and found to be linear in temperatures as T→ o and T ℓnT for 0.3 T_K ≤ T ≤ 0.6 T_K. A rise in (ΔC/T) for temperatures in the region 0 < T ≤ 0.1 T_K is predicted. These results are found to be in excellent agreement with experiments.

(vi) The existence of a critical temperature for Ferromagnetic coupling (J > o) is shown. On the basis of this the apparent contradiction of the simultaneous existence of giant moments and Kondo effect is resolved.

I. Foehn winds of southern California. II. Foehn wind cyclo-genesis. III. Weather conditions associated with the Akron disaster. IV. The Los Angeles storm of December 30, 1933 to January 1, 1934

I. Foehn winds of southern California.
An investigation of the hot, dry and dust laden winds occurring in the late fall and early winter in the Los Angeles Basin and attributed in the past to the influences of the desert regions to the north revealed that these currents were of a foehn nature. Their properties were found to be entirely due to dynamical heating produced in the descent from the high level areas in the interior to the lower Los Angeles Basin. Any dust associated with the phenomenon was found to be acquired from the Los Angeles area rather than transported from the desert. It was found that the frequency of occurrence of a mild type foehn of this nature during this season was sufficient to warrant its classification as a winter monsoon. This results from the topography of the Los Angeles region which allows an easy entrance to the air from the interior by virtue of the low level mountain passes north of the area. This monsoon provides the mild winter climate of southern California since temperatures associated with the foehn currents are far higher than those experienced when maritime air from the adjacent Pacific Ocean occupies the region.

II. Foehn wind cyclo-genesis.
Intense anticyclones frequently build up over the high level regions of the Great Basin and Columbia Plateau which lie between the Sierra Nevada and Cascade Mountains to the west and the Rocky Mountains to the east. The outflow from these anticyclones produce extensive foehns east of the Rockies in the comparatively low level areas of the middle west and the Canadian provinces of Alberta and Saskatchewan. Normally at this season of the year very cold polar continental air masses are present over this territory and with the occurrence of these foehns marked discontinuity surfaces arise between the warm foehn current, which is obliged to slide over a colder mass, and the Pc air to the east. Cyclones are easily produced from this phenomenon and take the form of unstable waves which propagate along the discontinuity surface between the two dissimilar masses. A continual series of such cyclones was found to occur as long as the Great Basin anticyclone is maintained with undiminished intensity.

III. Weather conditions associated with the Akron disaster.
This situation illustrates the speedy development and propagation of young disturbances in the eastern United States during the spring of the year under the influence of the conditionally unstable tropical maritime air masses which characterise the region. It also furnishes an excellent example of the superiority of air mass and frontal methods of weather prediction for aircraft operation over the older methods based upon pressure distribution.

IV. The Los Angeles storm of December 30, 1933 to January 1, 1934.
This discussion points out some of the fundamental interactions occurring between air masses of the North Pacific Ocean in connection with Pacific Coast storms and the value of topographic and aerological considerations in predicting them. Estimates of rainfall intensity and duration from analyses of this type may be made and would prove very valuable in the Los Angeles area in connection with flood control problems.

Heteroepitaxy of Group IV and Group III-V semiconductor alloys for photovoltaic applications

Photovoltaic energy conversion represents a economically viable technology for realizing collection of the largest energy resource known to the Earth -- the sun. Energy conversion efficiency is the most leveraging factor in the price of energy derived from this process. This thesis focuses on two routes for high efficiency, low cost devices: first, to use Group IV semiconductor alloy wire array bottom cells and epitaxially grown Group III-V compound semiconductor alloy top cells in a tandem configuration, and second, GaP growth on planar Si for heterojunction and tandem cell applications.

Metal catalyzed vapor-liquid-solid grown microwire arrays are an intriguing alternative for wafer-free Si and SiGe materials which can be removed as flexible membranes. Selected area Cu-catalyzed vapor-liquid solid growth of SiGe microwires is achieved using chlorosilane and chlorogermane precursors. The composition can be tuned up to 12% Ge with a simultaneous decrease in the growth rate from 7 to 1 μm/min^-1. Significant changes to the morphology were observed, including tapering and faceting on the sidewalls and along the lengths of the wires. Characterization of axial and radial cross sections with transmission electron microscopy revealed no evidence of defects at facet corners and edges, and the tapering is shown to be due to in-situ removal of catalyst material during growth. X-ray diffraction and transmission electron microscopy reveal a Ge-rich crystal at the tip of the wires, strongly suggesting that the Ge incorporation is limited by the crystallization rate.

Tandem Ga_1-xIn_xP/Si microwire array solar cells are a route towards a high efficiency, low cost, flexible, wafer-free solar technology. Realizing tandem Group III-V compound semiconductor/Si wire array devices requires optimization of materials growth and device performance. GaP and Ga_1-xIn_xP layers were grown heteroepitaxially with metalorganic chemical vapor deposition on Si microwire array substrates. The layer morphology and crystalline quality have been studied with scanning electron microscopy and transmission electron microscopy, and they provide a baseline for the growth and characterization of a full device stack. Ultimately, the complexity of the substrates and the prevalence of defects resulted in material without detectable photoluminescence, unsuitable for optoelectronic applications.

Coupled full-field optical and device physics simulations of a Ga_0.51In_0.49P/Si wire array tandem are used to predict device performance. A 500 nm thick, highly doped "buffer" layer between the bottom cell and tunnel junction is assumed to harbor a high density of lattice mismatch and heteroepitaxial defects. Under simulated AM1.5G illumination, the device structure explored in this work has a simulated efficiency of 23.84% with realistic top cell SRH lifetimes and surface recombination velocities. The relative insensitivity to surface recombination is likely due to optical generation further away from the free surfaces and interfaces of the device structure.

Finally, GaP has been grown free of antiphase domains on Si (112) oriented substrates using metalorganic chemical vapor deposition. Low temperature pulsed nucleation is followed by high temperature continuous growth, yielding smooth, specular thin films. Atomic force microscopy topography mapping showed very smooth surfaces (4-6 Å RMS roughness) with small depressions in the surface. Thin films (~ 50 nm) were pseudomorphic, as confirmed by high resolution x-ray diffraction reciprocal space mapping, and 200 nm thick films showed full relaxation. Transmission electron microscopy showed no evidence of antiphase domain formation, but there is a population of microtwin and stacking fault defects.

O papel do herói-mito na política de assentamento do nacional em povos desterrados pelo sistema colonial: uma leitura crítico-textual de Viva o povo brasileiro, de João Ubaldo Ribeiro e Sudjata ou A epopéia mandinga, de Djibril Tamsir Niane

A Literatura e a História sempre foram determinantes na evolução e afirmação de todos os povos que sofreram dominação estrangeira; o que, tantas vezes, levou os povos subjugados à perda de todas ou de uma boa parte de suas características específicas. Uma situação que ocasionou o questionamento das histórias destes povos - elaboradas pelos dominadores da cultura hegemônica à época e que, no nosso trabalho, são identificados como colonizadores. Este trabalho se propõe a visitar e salientar, através de duas obras bem características - a brasileira, Viva o Povo Brasileiro, de João Ubaldo Ribeiro e a senegalesa Sundjata ou a Epopéia Mandinga, de Djibril Tamsir Niane - não só o impacto das ocupações no cotidiano desses povos, mas também discutir e contribuir para a destruição da visão estereotipada desses povos espalhada pelos colonizadores antes de projetar a re-construção das identidades nacional e cultural corrompidas pela depend��ncia cultural, uma das conseqüências da colonização. Tal será levado a cabo através de uma atuação de primeiro e segundo planos do Herói-Mito que, ultrapassando o maravilhoso e o fantástico com que se identifica geralmente sua personagem, sublinha com insistência a evolução de uma entidade totalizadora como o povo-nação: o passado, o presente e o futuro. O Senegal e o Brasil, a partir de uma exploração detalhada de suas culturas, têm plena consciência dos laços mais do que estreitos que os definem como meio-irmãos, frutos de um pai...polígamo

离子液体在铈（IV）钍及稀土（III）萃取分离中的应用研究

本文对1-辛基-3-甲基咪唑六氟磷酸盐离子液体（[C8mim]PF6）在包头稀土矿分离钍以及攀西矿分离铈工艺中的应用作了初步探索。论文首先研究了伯胺N1923溶于离子液体对硫酸体系钍的萃取分离行为，考察了酸度、盐析剂浓度、萃取剂浓度等对N1923/IL萃取钍的影响，并与庚烷体系的萃取规律作了对比。在此基础上对萃取机理进行了探讨，提出了不同于分子溶剂体系的萃取机理，认为N1923/IL在水相有硫酸钠作为盐析剂时对钍的萃取为“胶束增溶”萃取机理。此外，钍对稀土的分离考察结果认为，虽然N1923/IL对钍的萃取效率降低，但在一定条件下钍对稀土仍能保持较高的分离系数。由此本文对N1923/IL应用于钍的分离实践作了初步评估。 论文的另外一部分工作研究了纯[C8mim]PF6及其与2-乙基己基膦酸二（2-乙基己基）酯（DEHEHP）的混合体系对硝酸铈（IV）的萃取性能。研究发现纯[C8mim]PF6本身对硝酸铈（IV）有良好的萃取选择性，机理考察结果认为铈（IV）的萃取是由于Ce4+离子在富硝酸根溶液中形成络阴离子Ce(NO3)62-并与离子液体的阴离子PF6—发生交换的结果。一种新型含铈离子液体[C8mim]2Ce(NO3)6的合成进一步证实了这一机理。反萃考察发现被萃入离子液相的铈（IV）用水可完全反萃，且萃取和反萃过程中因离子交换机理导致的离子液体流失可以通过添加适量离子液体组分的方法予以抑制。此外，本文考察了DEHEHP溶于[C8mim]PF6对于含氟硝酸体系铈（IV）的萃取行为，发现在一定条件下DEHEHP对铈（IV）的萃取能获得与分子溶剂中等同的萃取机理。在此基础上，采用DEHEHP/IL从氟碳铈矿分解液中进行分离铈和氟的研究，获得纯度为99.9%以上的纳米CeF3产品。由此我们提出一个将离子液体应用于攀西氟碳铈矿铈钍稀土分离流程的模型，为离子液体在稀土清洁分离流程中实现溶剂绿色化的目标提供了一个范例。

D&#8722;A型有机近红外材料的设计、合成及表征

近年来，随着近红外领域研究的深入，特别是光通讯工业的发展，迫切需要一大批具有良好发光性质的近红外材料。有机材料由于成本低、工艺简单和结构易调控等优点而备受关注。目前，对近红外有机发光材料的研究主要集中在两大类：一是稀土元素配合物；二是有机离子染料。但由于稀土元素的4f-4f跃迁是宇称禁阻的，其分子的激发需通过配体与中心离子的能量转移，发光效率低。同时有机离子染料由于静电相互作用，分子容易因聚集而导致发光萃灭，其器件结构主要采用主客体掺杂技术，存在着较强的主体材料发光和器件发光效率低等缺点。传统有机非离子型材料则不受上述因素的限制，可得到聚集态下高效的发光效率。本论文通过将电子给体与受体共轭连接，设计并合成了系列非离子型的窄带隙有机小分子，研究了它们在近红外电致发光等器件中的应用，主要工作内容和结果如下： (1)在分子内同时引入电子给体和受体，将它们共轭连接，设计并合成了系列D-π-A-π-D���的有机小分子，利用分子内电荷转移，实现近红外区域的吸收和发射。我们选择三苯胺和芴为电子给体，苯并双噻二唑及其衍生物为电子受体，苯、噻吩和吡咯为连接基团，得到的系列化合物的光谱及电化学性质能在很大的范围内进行调节。化合物的吸收光谱可从600nm至1400nm，发射光谱从900nm至1600nm范围内调节。化合物的带宽可从1.19eV减小到0.56eV。由于分子间的强相互作用，化合物在混合溶剂中可自组装成带状结构。同时该系列化合物在隔绝氧气的环境中有良好的光化学稳定性，可应用于电致发光或光伏器件中。 (2)多层器件结构是提高有机电致发光效率的有效方法，但前提是发光材料最好是可真空蒸镀。我们在前部分工作的基础上，合成了系列热稳定的可蒸镀型有机小分子。通过改变受体及给体结构可调节发光波长及效率。利用“掺杂剂/主体材料的思想”制备的电致发光器件，发光波长覆盖700nm到1500nm的范围，最长中心波长为1115nm。发光波长752nm时，器件最高外量子效率为1.12%。基于化合物IV-5制备的非掺杂器件，发光波长为1080nm，外量子效率为0.28%。该效率比基于有机离子染料的器件提高了近10倍。基于化合物IV-7的器件最大发射波长为1220nm，为迄今为止非掺杂有机电致发光器件中的最长发射波长。以上结果证明，该系列分子是良好的近红外电致发光材料。 (3)我们研究了含苯并双噻二唑分子与常见阴离子的相互作用关系，发现其只对CN-离子和F-离子有响应，而对其它阴离子如Cl , Br , I , AcO , H2PO4 , HSO4 , 和NO3 等则没有任何响应。并且通过将其中噻二唑环换成硝基，可实现对CN-离子和F-离子的区分。化合物V-2可高选择性的检测氰离子，其它离子的存在不会干扰检测信号，包括氟离子。检测信号为外观颜色的改变，可作为显色传感器。化合物V-3可定量检测CN-离子，检测极限为1μM。并且检测信号包括近红外发射的萃灭、可见发射的增强和吸收光谱的改变，多重检测信号可增加检测的可靠性。由于响应信号处于近红外区的生物波段，可应用于生物领域

膜基萃取稀土研究－中空纤维膜器中RE(III)、Th(IV)的萃取传质动力学及分离

首次使用两种新的聚偏氟乙烯中空纤维膜萃取法研究了HEH／EHP体系中钕、钐及铈及Cyanex272体系中镱、铒及钍的膜基萃取及分离。研究了膜材料性能。提出了膜萃取反应与液液萃取相同，且均为一级反应；高料液pH值条件下的H~+优先于NH_4~+的传质规律；氨化萃取剂可降低传质阻力；膜萃取机理为伴有界面反应的扩散控制机理及膜孔径对萃取机理的影响。利用钍的传质速率远大于镱的传质速率的特点，实现动力学竞争分离钍和镱。通过界面反应动力学研究，得到了各组分的反应动力学方程、反应速率常数K及相关组分的分离系数。将氨离子选择电极与流动注射分析相结合，实现了氨离子的自动在线分析。为膜萃取技术的工业化提供有价值的基本参数。

Tin (IV) phthalocyanine oxide: An air-stable semiconductor with high electron mobility

Air-stable n-type field effect transistors were fabricated with an axially oxygen substituted metal phthalocyanine, tin (IV) phthalocyanine oxide (SnOPc), as active layers. The SnOPc thin films showed highly crystallinity on modified dielectric layer, and the electron field-effect mobility reached 0.44 cm(2) V-1 s(-1). After storage in air for 32 days, the mobility and on/off ratio did not obviously change. The above results also indicated that it is an effective approach of seeking n-type semiconductor by incorporating the appropriate metal connected with electron-withdrawing group into pi-pi conjugated system.

Phthalocyanato tin(IV) dichloride: An air-stable, high-performance, n-type organic semiconductor with a high field-effect electron mobility

Phthalocyanato tin(IV) dichloride, an axially dichloriniated MPc, is an air-stable high performance n-type organic semiconductor with a field-effect electron mobility of up to 0.30 cm(2) V-1 s(-1). This high mobility together with good device stability and commercial availability makes it a most suitable n-type material for future organic thin-film transistor applications.

Self-immobilized titanium and zirconium catalysts with phenoxy-imine ligands for ethylene polymerization. X-ray crystal structure of bis(N-(3-tert-butylsalicylidene)-4 '-allyloxyanilinato) zirconium(IV) dichloride

Four self-immobilized FI catalysts with allyl substituted phenoxy-imine ligands [{4-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2) MCl2] (1: M = Ti: 2: M = Zr), [{3-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2)MCl2] (3: M = Zr), [{4-(CH2=CHCH2-2,6-(iso-C3H7)(2))C6H5N=CH-C6H3(3,5-(NO2)(2))O}(2)MCl2] (4: M = Zr) have been synthesized and characterized. The molecular structure of 2 has been determined by X-ray crystallographic analysis. The results of ethylene polymerization showed that the self-immobilized titanium (IV) and zirconium (IV) catalysts 1-3 kept high activity for ethylene polymerization and 4 showed no activity. SEM showed the immobilization effect could greatly improve the morphology of polymer particles to afford micron-granula polyolefin as supported catalysts.