Since Swiatoslaw Trofimenko first reported their synthesis in 1966, poly(pyrazolyl)borate ligands, [R”ₓB(pz，ᴿ⋅ᴿ’)₄₋ₓ], have found widespread utility in modern coordination chemistry, undoubtedly as a consequence of the numerous facets of the ligand scaffold that can be readily altered. Relative to the extensive efforts directed towards the incorporation of pyrazolyl moieties with different substituents and towards the installation of groups other than hydrogen on the bridgehead boron, comparatively few attempts have been dedicated to elucidating synthetic approaches to altering the identity of the bridgehead atom itself. Such manipulations have the potential to generate new compounds that exhibit both structural and electronic properties previously unobserved or inaccessible for the parent boron compound, and the research summarized herein is motivated both by the paucity of these derivatives and by this potential. Chapter 1 explores the use of aluminum and gallium as linker atoms to afford heavier congeners of traditional poly(azolyl)borates. This study has utilized LiEH₄ (E = Al, Ga) in place of LiBH₄, and significantly has afforded the first structurally characterized examples of tris(pyrazolyl)hydrogallates and of tris(pyrazolyl)methylgallates featuring substituted pyrazolyl groups. Moreover, the structures of {[R”ETpᴿ⋅ᴿ’]Li}₂ (E = Al, Ga) have been found to vary as a consequence of the identity of both the pyrazolyl substituents (R, R’) and the substituent on the linker atom (R”), and in some instances differ significantly from the structures of the corresponding boron derivatives. Additionally, the reactions of LiEH4 with tert-butylmercaptoimidazole, HmimBut, have afforded the first examples of tris(mercaptoimidazolyl) ligands to feature aluminum and gallium bridgeheads. The molecular structures of these derivatives similarly display interesting coordination modes which, in some cases, contrast greatly to those of the parent boron ligands. In Chapter 2, synthetic approaches for the preparation of novel dianionic tris(pyrazolyl) ligands, obtained via the use of magnesium and zinc as linker atoms, are summarized. Interestingly, the otherwise neutral {[MeMTpᴹᵉ²][Li₂]} fragment is found to associate with an additional Lipzᴹᵉ² molecule, thereby affording a series of [MeMTpᴹᵉ²][Li3(pzᴹᵉ²)Ln] compounds in which each lithium is coordinated to two pyrazolyl nitrogen atoms. Both chloride and iodide anions can also serve as capping ligands for the {[MeMTpᴹᵉ²][Li₃]}+ moieties, suggesting that the trilithio scaffold can be viewed as a trifold receptor for anions. Additionally, the tetrakis(pyrazolyl) derivatives, [(THF)2Li{μ-[M(pzᴹᵉ²)₄]}Li(THF)₂], have also been prepared and structurally characterized. Chapter 3 details the preparation, characterization, and reactivity of symmetric homodinuclear magnesium and zinc complexes, [MeM(pzᴹᵉ²)₃MMe]–, in which the two metal centers are bridged by three exo-bidentate pyrazolyl ligands. The bridging of two identical metal centers by more than two pyrazolyl groups is a rare structural motif, and so [MeM(pzᴹᵉ²)₃MMe]– represent important contributions to not only the chemistry of magnesium and zinc, but also to that of the pyrazolyl ligand. The reactivity of [MeZn(pzᴹᵉ²2)₃ZnMe]– towards protic reagents and trimethyltin halides has been investigated, and has most notably afforded a rare example of an anionic terminal zinc fluoride complex, [FZn(pzᴹᵉ²)₃ZnF]–. Additionally, the homodinuclear zinc hydride complex, [HZn(pzᴹᵉ²)₃ZnH]–, has been obtained and structurally characterized, and represents the first example of an anionic terminal zinc hydride compound. The spectroscopic characterization of both [HZn(pzMe2)₃ZnH]– and its isotopologue, [DZn(pzᴹᵉ²)₃ZnD]–, are summarized, as are the results of preliminary reactivity studies with CO2 and CS2, which suggest that insertion of these heterocumulenes into the Zn–H bonds is facile and affords, inter alia, zinc formate and zinc dithioformate species, respectively. Chapter 4 summarizes the exocyclic N-methylation of Nitron(S), a 1,2,4-triazole thione derived from Nitron. The molecular structures of both Nitron(S) and of the methylated derivative, Nitron(S)Me, are reported, and a comparison of metrical data indicates that (i) the structures of these thiones differ significantly from the dominant tautomer of Nitron and (ii) the structures of these thiones compare favorably with the NHC tautomer of Nitron. Analyses of these compounds using natural bond orbital (NBO) and natural resonance theory (NRT) methods are in accord with the experimental structures.

Thesis advisor: Shih-Yuan . Liu / Chapter 1. Use of boron as a pharmacophore is as growing but still underdeveloped strategy for expanding chemical space in biomedical research. In addition to more established methods of incorporating boron in drug development, an attractive and emerging method of introducing boron into biologically active compounds is through boron-nitrogen containing heterocycles. In particular, the Liu group has focused on exploring the interactions of monocyclic 1,2-azaborines in biological space. In order to install complicated chemical functionality needed for further studies, methods for late stage functionalization of 1,2-azaborines must be developed. Described herein is a method for functionalizing 1,2-azaborine at the C3- and C5-positions, with bromine and iodine handles, respectively. Chapter 2. Described is the application of the turbo Grignard reaction to 1,2-azaborines bearing a B–Cl bond. The reaction utilizes iPrMgCl·LiCl to form aryl carbon nucleophiles and is tolerant of sensitive functional groups such as nitriles and esters. Development of the reaction obviates the need to use toxic organotin reagents to install aryl groups at the B-position that bear sensitive, electrophilic functionalities. / Thesis (MS) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

The adsorption of boron by Aiken clay loam and Vernal sandy loam was studied in the boron equilibrium concentration range of 0 to 40 ppm. Adsorption data were obtained at 11, 20 and 30°C. The data were analyzed by the application of the Langmuir adsorption isotherm. It was concluded that, in both Soils, the adsorption of boron occurred on three distinct sites or regions. The acid ferrigenous Aiken soil had a higher adsorption capacity for boron than the calcareous Vernal soil when compared on a unit mass basis. On the unit area basis, however, the Vernal soil adsorbed more boron than the Aiken soil. The isoteric heat of adsorption showed that boron reacted more energetically with the Vernal soil. The calculated 6H values were -7.6 K cal/M and -3.3 K cal/M for Vernal and Aiken soils, respectively. The capacity of both soils to adsorb phosphorus was higher than their capacity to adsorb boron. The presence of adsorbed phosphate did not greatly reduce the amount of boron adsorbed by either soil studied. In the Vernal soil, phosphate was three times more efficient in replacing boron than in the Aiken soil. Also, chloride was found to desorb more boron from the Aiken soil than phosphate. However, neither phosphate nor chloride was found to be effective in reducing to any great extent the adsorption of boron by the two soils studied.

Sintering parameter effects on the microstructure of boron carbide and boron carbide/titanium diboride composites are investigated. The resulting microstructure and composition are characterized by scanning electron microscopy (SEM), x-ray microscopy (XRM) and x-ray diffraction (XRD). Starting powder size distribution effects on microstructure are present and effect the mechanical properties. Reactive spark plasma sintering introduces boron nitride (BN) intergranular films (IGF's) and their effects on fracture toughness, hardness and flexural strength are shown. Mechanical testing of Vickers hardness, 3-point bend and Chevron notch was done and the microstructural effects on the resulting mechanical properties are investigated.

付記する学位プログラム名: 充実した健康長寿社会を築く総合医療開発リーダー育成プログラム / 京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21793号 / 工博第4610号 / 新制||工||1718(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 田中 一生, 教授 秋吉 一成, 教授 大内 誠 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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Neutron imaging is a non-destructive technique with many applications in diverse fields such as industrial quality assurance, archaeology, and border security. However with the high cost of the standard fill gas 3He and the high cost of scaling conventional digital imaging systems to large areas its applications are limited. Here is presented the proof of concept for a gaseous neutron imaging system utilizing a 10B4C solid state converter and THGEM technology and 2D passive delay line readout. THGEMs used for signal amplification can be produced cost effectively and in large areas by PCB manufacturers. This combined with the reduced channel processing requirements of delay lines over individual pixel readouts results in a cost-effective and scalable system when compared to similar designs using solid state multipliers such as silicon photomultipliers. Here is presented a proof of concept of this imaging system with data acquisition accomplished by digitization and offline image reconstruction achieving mean X and Y resolution of <sigma_x> = (1.37+-0.24) mm and <sigma_y> = (1.15+-0.13) mm respectively. Studied in parallel with this system is the effectiveness of gadolinium oxide based paint as a thermal neutron shield and image contrast agent. / Thesis / Doctor of Philosophy (PhD) / In this work is presented the development process of a novel and cost-effective neutron imaging system capable of imaging soft biological and dense materials that X-rays are unable to penetrate. Such a system may be scaled to large areas for many applications including the study of large archeological objects or employed as a security measure to monitor border checkpoints for transportation of controlled radioactive materials.

The present thesis comprises synthesis and stoichiometric model reactions of well-defined NHC-stabilized copper(I) complexes (NHC = N-heterocyclic carbene) in order to understand their basic reactivity in borylation and cross-coupling reactions. This also includes the investigations of the reactivity of the ligands used (NHCs and CaaCs = cyclic alkyl(amino)carbenes) with the substrates, i.e. diboron(4) esters and arylboronates, which are addressed in the second part of the thesis. / Die dargelegte Arbeit gliedert sich in zwei Teile. In einem ersten wird die Synthese sowie stöchiometrische Modell-Reaktionen von definierten NHC-stabilisierten Kupfer(I)-Komplexen (NHC = N-heterocyclisches Carben) untersucht, um Einblick in das grundlegende Reaktionsverhalten in Borylierungs- und Kreuzkupplungsreaktionen zu erlangen. Der zweite Teil adressiert die Reaktivität der eingesetzten Liganden (NHCs und CaaCs = cyclische Alkyl Amino Carbene) gegenüber verwendeten sowie möglichen Substraten (Arylboronsäureester und Diboran(4)-Verbindungen).

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