Adding an ethylene bridge between non-adjacent nitrogens of tetraazamacrocycles has produced extremely kinetically stable transition metal complexes since the early 1990's. These topologically complex and rigid ligands make it difficult for the usual stepwise dissociation processes to remove the ligand from a metal ion, even under harsh conditions. Increasingly sophisticated examples of these ligands and their complexes have found continuing success in applications where metal complex stability under harsh conditions is paramount, such as aqueous oxidation catalysis, biomedical imaging, and medicinal inorganic complexes. As a potential path towards additional strong-binding azamacrocyclic ligands, we have explored potential routes to ethylene cross-bridged pentaazamacrocycles. The additional nitrogen donor is a predicted advantage for even greater stability, yet the larger ring sizes required may reduce the rigidity of the resulting complexes. In this presentation, we will outline several synthetic routes we have taken towards a set of cross-bridged pentaazamacrocyles. Also, we present the initial characterization of the transition metal complexes of these novel ligands.

Developing methods to cross-bridge pentaazamacrocycles

2019 Spring National Meeting

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