Rong Cai

Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Bjorn C G Soderberg

Committee Co-Chair

Xiaodong Shi

Committee Member

Patrick S Callery

Committee Member

Jessica M Hoover

Committee Member

Jeffrey L Petersen

Committee Member

Brian V Popp

Abstract

Homogeneous gold catalysis has envisioned a rapid development during the past decade due to the remarkable efficiency of Au(I) in alkyne and allene activation. Air and thermally stable triazapentalene zwitterionic compounds (TAPZ) were prepared through Au(I)-catalyzed triazole-alkyne 5-endo-dig cyclization. While effective gold catalyst turnover was achieved, the stability of these new 10-pi-electron bicyclic structures was also significantly improved through the introduction of electron-withdrawing groups, which allowed the further application of these fluorescent dyes in cell imaging.;Silver salts are generally used for the activation of LAuCl through Cl - removal, and they are assumed to be innocent in Au(I) catalysis. For the first time, experimental evidences from XPS and 31P NMR were obtained to confirm that the combination of Ag+ cation with [L-Au]+ resulted in the formation of different complexes in solution. Cationic gold was proved to be inactive without the presence of silver salts and it could be re-activated by the addition of silver salts in several precedent reactions. This study revealed a long-overlooked "silver effect" and initiated a mechanistic reconsideration in gold catalysis.;Compared with Au(I) catalysis, redox gold catalysis is far less developed due to the relatively high oxidation potential of Au(I)/Au(III). With the assistance of bpy ligand, gold-catalyzed sp-sp2 and sp 2-sp2 cross-coupling reactions are accomplished with aryldiazonium salts as the coupling partner. The gold(I) species were oxidized to gold(III) by diazonium without any external oxidants. Monitoring the reaction with NMR and ESI-MS provided strong evidence for the nitrogen extrusion as the key step followed by Au(III) reductive elimination. To further extend the scope of the gold redox chemistry with aryldiazonium salts, gold-catalyzed Sandmeyer reactions were investigated using different nucleophiles, forming C-Br, C-S and C-P bonds in high yields and selectivity.;Despite the high efficiency of gold catalysts, their application for large-scale synthesis is limited due to the high catalyst cost. A recyclable triazole-gold catalyst, which dramatically decreases the catalyst cost, is prepared using porous polymer as the support ligand. This unique catalyst is successfully applied into previously challenging transformations with good efficiency and recyclability.;Visible light photocatalysis is an efficient and green method that can convert the energy from visible light to chemical energy. One challenge to accomplish the catalytic cycle is the matching of redox potential between the substrate and the photocatalyst. With the easily tunable triazole ligands, N-2-Aryl chelated triazole-Ir(III) complexes with various substituents were prepared. These Ir(III) complexes were tested in photoredox catalysis with different reactivities related with their tunable photoredox potentials.

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