The good without the bad: Selective chelators for beryllium encapsulation

Abstract

Beryllium is an indispensable metal. Its unmatched combination of unique properties such as extreme strength, low density and high machinability has made it vital in the automotive, nuclear, space, medical, defence sectors and other consumer industries. However, beryllium is considered the most toxic non-radioactive element on the planet. It is also a class one carcinogen and the cause of chronic beryllium disease (CBD). Surprisingly, this fact has not deterred its use in manufacturing. Therefore it is imperative that chemical agents be developed for better detection and remediation of beryllium in the environment and as therapies for individuals exposed to this element. The goal of this research was to develop strong, selective chelating agents for the encapsulation of beryllium. Furthermore a greater ex-ploration of beryllium fundamental coordination chemistry was under-taken with an investigation of binding preferences of the Be2+ cation. The introduction begins with a brief overview of beryllium solu-tion chemistry. Following this is a comprehensive review of the Be2+ coordination chemistry with an investigation into existing organic and inorganic ligands with an emphasis on hard nitrogen and oxygen donor containing ligands. This then moves on to a brief description of the selected ligand design based on the fundamental coordination prefer-ences of Be2+. The main ligand motif will be based on a di-pyridyl scaffold with selected chelating pendant groups, allowing the formation of tetradentate complexes which can form the desired six-membered chelate rings with Be2+ cations. Chapter Two explored the synthesis of a ligand based a dipyrrin pendant group. The corresponding dipyrromethane was used as the starting point. While coupling of this dipyrromethane directly on to a dipyridyl scaffold was unsuccessful, the same dipyrromethane con-taining a one pyridyl group in the form of an acyl-pyridyl unit served as a reasonably good candidate for the successful coupling of the last pyridine group. Furthermore, synthesis of a modified dipyrrin ligand with the inclusion of hydrogen-bonding buttressing groups was also attempted. Chapter Three explored the synthesis of a ligand containing a mo-tif based on a hydroxy-phenyl imidazole moiety. The hydroxyphenyl imidazole moiety was synthesised and used as a starting point. The brominated analogue of the hydroxyphenyl imidazole moiety was suc-cessfully coupled to a di-pyridyl scaffold containing a nitrogen at the center scaffold position through a modified Ullman type reaction. DFT studies of the ligands synthesised and preliminary complexation studies were conducted using boron and aluminium ions as safe analogues and are described in chapters Four and Five. ESI-MS studies were also used for the study of the Be-ligand complexes, allowing their synthesis on a small scale and minimising exposure to beryllium.