Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1911. / Reprinted from Journal of physical chemistry, vol. 16, no. 1. Includes bibliographical references.

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Thesis advisor: Shih-Yuan Liu / Thesis advisor: Marc Snapper / Organoboron compounds are widely used in organic synthesis and medicinal chemistry. It has been shown that organoboron compounds can undergo a vast quantity of transformations, especially stereospecific reactions. Boron enolates and their reactivity are less explored in the field of organic chemistry. In enolates, boron can be bound to oxygen or carbon. The boron-carbon enolates are of interest for having the potential to engage in stereospecific organoboron chemistry via the stereospecific carbon connected to the boron atom. Two methods of synthesizing boron-carbon enolates are through quaternized and unquaternized boron centers. While quaternized boron-carbon enolates are more studied, unquaternized boron-enolates represent a gap in the field. To date only four unquaternized boron-carbon enolates have been isolated and characterized with only one of the compounds engaging in organoboron chemistry. Herein I report the synthesis, isolation, and characterization of a boron-carbon enolate containing 1,2-azaborine as the organoboron analog. / Thesis (MS) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Part I: Compounds of the type benzo(group VI)azole (I) were treated with diborane using standard vacuum line techniques. The group VI elements were oxygen. sulfur. and selenium. Initially. an insoluble borane adduct formed which spontaneously reduced and replaced carbon in the hetero-ring by boron via an unstable intermediate either (II) or (III). For example. benzoxazole reacted to produce 2-H-3-methyl-l.3.2- benzoxazaborole (IV). The 2-H-3-alkyl-l,3.2-benzo(group VI)azaboroles (V) were easily purified. produced in high yield, and upon methanolysis yielded N-alkyl-2-(group VI)anilines (VI). These boroles were characterized by IR, H-l and B-ll NMR spectra, and mass spectroscopy. Part II: Kinetics of the polymerization of imidazole-borane in the presence of diborane was followed by monitoring hydrogen production at 30°C. Pseudo first-order kinetics was observed at all ratios of diborane to irnidazole-borane, and the observed rate constant increased linearly with excess diborane. A mechanism is proposed in which the diborane acts as a catalyst. Half the hydrogen molecule comes from the diborane, while the other half comes from the nitrogen-bonded hydrogen on imidazole-borane. Hydrogen is formed when diborane reacts with imidazole-borane in a slow step. followed by fast coupling with another imidazole-borane and regeneration of diborane. The structure of the polymer is shown below (VII). and the average size of the polyme1 was 32-38 units.

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Three heterosubstituted boranes were successfully synthesized from the corresponding amines and borane dimethyl sulfide (BH3·DMS) in high yields, and were noted to be significantly more stable than the analogous dioxo-compounds. In situ 11B NMR spectroscopy indicated that the mechanism of the reaction to form these boranes contains two intermediates and supports a step-wise addition mechanism. 15N NMR spectroscopic analysis of the boranes identified a downfield shift in the location of the nitrogen signal from the typical amine region towards the aromatic region, supporting the theory of electron back-donation from the nitrogen lone pair to the boron atom’s vacant pz-orbital. The three boranes proved to be suitable hydroboration reagents under microwave-assisted conditions, with Wilkinson’s catalyst and a rhodium(I) carbonyl hydride catalyst both showing catalytic ability, however yields were noted to be dependent on the borane, the olefin and the catalyst. Twelve heterosubstituted boranes were successfully synthesized in high yields as products from condensation reactions between diamines and boronic acids both in solution and under microwave-assisted solvent-free conditions, which resulted in the reaction time being reduced from three hours to 15 minutes. 15N NMR spectroscopic analysis of these compounds showed a similar downfield shift in the amine signal as was observed previously, lending support to the electron back-donation explanation for the stability of these compounds. Crystals suitable for X-Ray diffraction analysis were grown for four 1,8-diaminonaphthalene-based boranes, and analysis of the data showed that the compounds are not planar as originally thought, rather there is a degree of torsion inherent in each of the structures, ranging from a slight (3-4%) to a substantial deviation (19-20%). It was shown that heterosubstituted boranes can be used in Petasis reactions as the organoborane reagent in a number of cases, although the reaction conditions used were not optimized for these compounds. Microwave irradiation was also successfully employed in the Petasis reactions, which reduced the reaction time from 48 hours to 10 minutes. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Zhang, Jian. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 263-289). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Zheng, Fangrui. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 181-197). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The high temperature transformations of trialkylboranes were investigated in the range: 50- 200 ºC. The extent of dealkylation was found to be linked to temperature with ca. 10% octene liberation from tri-n-octylborane at 150 ºC in the absence of bulk solvent. Analysis of the oxidised samples from the dealkylation investigation shows that, whereas the control experiment shows no back-isomerisation of tri-n-octylborane at 150 ºC, the addition of 10 mol% of DMF, DMSO, HMPA and trimethoxyphosphate results in back-isomerisation of the alkyl chain. In general, the addition of Lewis base catalyst was found to enhance the extent of dealkylation. In a supporting 11B NMR spectroscopy study to understand the interaction of trialkylboranes and Lewis bases, the interactions of a series of oxygen and phosphorous donor Lewis bases with tri-n-butylborane were found to be favourable, as indicated by large negative binding enthalpy ( HBIND) and entropy ( SBIND) values. Only the trialkylamine Lewis bases were found to have unfavourable interactions with tri-nbutylborane, as indicated by positive HBIND and SBIND values. The results also show that the chemical shift of the adduct at infinite dilution ( 11 B = ) is not as reliable a measure of the interaction between the two species and that correlation of binding constant (logKBIND) at 25.0 ºC to GBIND defines a linear trend that orders the Lewis bases according to spontaneity of the interaction with the strength of the dative bond formed. The applicability of 11B NMR spectroscopy to the study of the reactions of boranes and alkylboranes was extended to the investigation of the reduction of nitriles by BH3.SMe2 in dichloromethane (15-30 ºC). Results from the kinetic study indicate that the overall reduction with BH3.SMe2 is associative ( Sactivation = -71 ± 10 J K-1 mol-1), with the dependence of kobs data on SMe2 concentration highlighting the importance of the dissociation of the SMe2 from BH3 to the reduction process. The lack of reaction with propionitrile and benzonitrile at 25 ºC can be attributed to lack of stability of their adducts with BH3 as demonstrated by the small equilibrium constants for the formation of their adducts with borane; as determined by 1H NMR spectroscopy and further illustrated by computational calculation of their energies at the B3LYP/6-31G* level of theory. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

This thesis focuses on the investigation of the optoelectronic, photo and thermal- responsive properties of organoboron compounds. In search of blue phosphors for phosphorescent organic light emitting diodes, new triarylboron functionalized phosphorescent Pt(II) complexes were synthesized and their device performances were evaluated. In Pt(II) complexes with the 2-phenylpyridyl N,C-chelate ligand and an acetylacetonato ancillary ligand, it was found that BMes2 substitution at the 4’ position of the phenyl ring can increase the phosphorescent emission energy, compared to the 5’-BMes2 substituted analogue. This occurred without substantial loss of luminescent quantum efficiency. At 100 cdm-2 luminance, electroluminescence devices with the newly synthesized Pt(II) complexes as emitters have achieved external quantum efficiency of ~ 4.7-13.4%. Tuning of the photo-responsive properties of biaryl N,C-chelate dimesitylboron compounds was achieved by functionalization with either a bisthienyl moiety or ferrocene unit. It was demonstrated that the bisthienyl unit has the ability to completely stabilize a N,C-chelate boryl chromophore toward photoisomerization. With the ferrocene unit being part of the chelation backbone of BMes2 moiety, the B−N bond of molecule B(2-ferrocenyl-N-Me-benzimidazolyl)Mes2 was found to undergo a dynamic dissociation/association process in solution, leading to its slow hydrolysis under ambient conditions. The oxidized ferrocenium species has a notable spin delocalization through space from the Fe(III) center to a flanking mesityl group. To further expand the photochromic family based on pyridyl N,C-chelate dimesityboron compounds, a systematic study was carried out with the pyridyl N donor replaced by N-heterocyclic carbene donor and azolyl, benzoazolyl N donors. These new classes of organoboranes all underwent transformation to their corresponding dark isomer in a similar fashion as the pyridyl N,C-chelate dimesitylboron. However, a second-step photoisomerization was observed in the NHC,C-chelate dark isomer via a “borylene”-like intermediate. The thiazolyl, benzoazolyl N,C-chelate dark isomers demonstrate multi-structural transformations, which include hydrogen atom transfer, 1,3-boryl shift and diastereomer interconversion via a spiropyran type ring-opening/closure process. The imidazolyl N,C-chelate dark isomer exhibits a consecutive photochromism phenomenon, namely an interconversion between azaboratabisnorcaradiene and azabenzotropilidene derivatives. The calculated mechanism for this bares an interesting resemblance to that of the “walk” rearrangement in norcaradiene. / Thesis (Ph.D, Chemistry) -- Queen's University, 2014-06-23 20:55:20.399