Date on Master's Thesis/Doctoral Dissertation

5-2018

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Hammond, Gerald B.

Committee Co-Chair (if applicable)

Noble, Mark E.

Committee Member

Noble, Mark E.

Committee Member

Richter, Natali B.

Committee Member

Ng, Chin K.

Author's Keywords

Long-range electrostatic interactions; counterion effect; hydrogen bonding; gold catalysis; HF reagent

Abstract

Our research focus is on applying two long range electrostatic interactions--coulombic interaction between ion pairs and hydrogen bonding—to two tasks: exploring counterion effects in gold catalysis and utilizing hydrogen bonding for fluorinating reagent development. Cationic gold catalysis is considered one of the most important breakthroughs in organic synthesis over the past two decades. A wealth of empirical information on counterion effects is now available regarding homogeneous gold catalysis. However, the rational understanding of the counterion effect on reactivity is still elusive. We proposed a widely applicable model to rationalize the kinetic effect in gold catalyzed reaction. We first solved the problem of the silver effect that existed in gold catalyst and provided a more stable gold catalyst preparation protocol. We discovered that the presence of silver activators almost always had adverse effects in many gold catalyzed reactions. However, using a pre-formed L-Au+X- complex by removing excess AgX before the reaction avoided this problem. The deleterious silver effect may be caused by the interaction of silver salts with key gold intermediates like vinyl gold complex in the gold catalytic cycle. With the new method of catalyst preparation, we investigated the counterion effect in various cationic gold catalyzed reactions. We found that gold affinity and hydrogen bonding basicity of counterions play critical roles in the reactivity of cationic gold catalysts. The impact of our studies may not be limited to gold catalysis but may also provide guidance in transition metal catalysis in general. We then applied the hydrogen bonding basicity scale of different anions for the development of a new generation of HF-based reagents. We utilized a novel acidic but strong hydrogen bonding acceptor as a stabilizer to fixate gaseous and toxic hydrogen fluoride as liquid. This new reagent has several advantages such as being inexpensive, easily handled, and more acidic than other commercially available HF reagent. We then utilized this HF reagent on the hydrofluorination of various highly functionalized alkenes. The excellent functional group tolerance, exclusive Markovnikov addition regioselectivity and high atom economy may facilitate the preparation of other fluorinated products at both the lab and industrial scale.

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