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theses

Organoboranes have been widely used for catalytic transformations, polymerizations, small molecule activation, anion and glycol sensing and construction of electronic materials. These remarkable applications commonly benefit from the electron-deficient nature of tricoordinate boron, i.e., its empty p-orbital can accommodate a lone pair of electrons or participate in conjugation of extended π-systems. Therefore, approaches to enhance the Lewis acidity of the boron center are desirable, and different strategies have been introduced with this aim, including (1) installation of electron withdrawing pendant groups such as pentafluorophenyl groups; (2) generation of cationic borenium species and (3) incorporation of tricoordinate boron into anti-aromatic systems such as borole derivatives. Recently, much effort has been directed to the preparation of the so-called “Frustrated Lewis Pair” (FLP) and the application of their unquenched relativity for catalytic transformations. However, chiral versions of highly Lewis acidic organoboranes remain scarce. On the other hand, planar chiral ferrocenes have proven to provide rigid frameworks for transition metal ligands such as phosphines and amines, which have been successfully applied to the asymmetric hydrogenation of alkenes, ketones and other processes. This dissertation describes our efforts towards the stereoselective synthesis of ferrocene-based multifunctional organoboranes with unique geometric features and electrochemical properties: (1) the 1,2-disubstituted ferrocene backbone provides a rigid planar chiral environment; (2) the reversible oxidation of the ferrocene unit can be exploited for redox active Lewis acids, Lewis pairs and ambiphilic ligands. We demonstrate that a series of highly Lewis acidic derivatives can be synthesized via installation of electronic deficient pentafluorophenyl groups and generation of a borenium cation. The planar chiral borenium cation species serves as a catalyst for the asymmetric hydrosilylation of ketones. Next, we concentrated our attention on the construction of planar chiral borane-pyridine systems: the interactions between the borane and pyridine units can be tuned by introduction of different steric and electronic effects. The coordination of a planar chiral diferrocenylphosphaborin ligand to transition metals is also investigated. We discovered that the F- binding to the boryl moiety leads to an enhancement of the electron donating properties as a phosphine ligand by monitoring the v(CO) frequency of the corresponding Vaska-type rhodium complex.

ETD_5574

Ph.D.

Includes bibliographical references

Includes vita

by Jiawei Chen

doi:10.7282/T3MW2FD5

ETD doctoral

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