Bipyridine Ligands for use in Polymer-Supported Iridium Catalyzed C-H Borylation

Abstract

Polymer-supported catalysis has shown high recyclability of precious metal catalysts. This project explored several synthetic routes to make a polymer-support linker to use in organic synthesis.
Bipyridine ligands, such as 4, 4’-tert-butyl-bipyrine with an iridium precatalyst afford a highly efficient C-H borylation, but studies of polymer-supported bipyridine ligands have not been extensively researched. With an aim to exploring this approach to allow recycling of the expensive iridium catalysts synthesis of new bipyridine ligands were undertaken. A modular synthesis was envisaged using Stille cross-coupling to generate a model compound. However, no desired bipyridine compounds could be synthesized.
Alternative methods were then employed to synthesize the polymer-supported ligands. The initial aim was to couple two substituted pyridine to generate a bipyridine. Several methods have been investigated. The best route involved the cross-coupling of a pyridine N-oxide and 2-bromopyridine. However this only gave the desired product in low yield. Then attention turned to functionalize preformed 4, 4’-disubstitued-2, 2’-bipyridine, however, ligands suitable for immobilisation onto a polymer resin were not successful generated. Recently, excellent yields of pyridine containing biaryls through the direct addition of aryl lithiation to pyridines have been reported. This aroused interests for generating bipyridine ligands in an analogous fashion. Although this new route to synthesis bipyridine ligands was not completed, this showed a high possibility for the generation of polymer-supported ligands and is worthy of further study.
Full details of this research are presented in chapter 2. Experimental procedure and data is in chapter 4.