o-Aminobenzaldehyde (oab) is known to self-condense under a variety of reaction conditions, including in the presence of metal ions. Different polymeric Schiff-base condensates are produced depending on the coordination preferences of a given metal ion, including the tetrameric ligand known as TAAB (tetrabenzo[b,f,j,n][l,5,9,13]tetraazacyclohexadecine). The objective of this research is to design an extended analogue of oab to give a larger self-condensate ligand to accommodate larger metal ions. Increasing the size of the macrocyclic ligand can potentially allow lanthanide(III) ion complexes to form. Lanthanides are highly paramagnetic, making macrocycle lanthanide complexes good candidates for contrast agents for magnetic resonance imaging (MRI).<br/>The ligand precursor is formed in a six-step synthesis starting with the generation of the 8-nitroquinaldine from 1-nitroaniline and crotonaldehyde with phosphotungstic acid as a catalyst. The 8-nitroquinaldine is brominated at the aromatic methyl. Tribromonitroquinaldine is hydrolyzed with sulfuric acid to form the carboxylic acid. The final steps involve the reduction of the nitro group using hydrazine hydrate with zinc phthalocyanine as a catalyst, forming the amino acid, followed by reduction of the acid to an alcohol with lithium aluminum hydride and finally oxidation of the alcohol with manganese(IV) oxide to give 8-amino-2-quinolinaldehyde. The ligand is synthesized by Schiff-base self-condensation with three equivalents of 8-amino-2-quinolinealdehyde using a metal ion as a template. Progress toward the synthesis and characterization of the ligand precursor and the formation of a lanthanide complex will be presented.

Synthesis and characterization of a larger neutral macrocycle for transition and lanthanide(III) metal complexes

249th National Meeting (2015)

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