Charged Behaviour from Neutral Ligands: Synthesis and Properties of N-Heterocyclic Pseudo-amides

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Deprotonation of the 1-isopropyl-3-(phenylamino)pyridin-1-ium iodide gives the corresponding neutral betaine, which is formalised as a pyridinium-amido ligand when coordinated to a metal. Spectroscopic, structural and theoretical methods have been used to investigate the metalligand bonding, ligand dynamics and electron distribution. Collectively, the data show that the ligand can be characterised as a pseudo-amide and is a strong donor akin to alkyl phosphines and N-heterocyclic carbenes. Furthermore, rotation about both N substituent C?N bonds occurs, which is in contrast to the two alternative pyridinium positional isomers that exhibit neutral resonance structures. For comparison, compounds and complexes derived from norharman were prepared, which contain an additional C?C bond supporting conjugation and the accessibility of a neutral resonance structure. Notwithstanding the formal neutral structure, norharman-derived ligands are comparably strong donors, and have the additional advantage of exhibiting stability to dioxygen and water.

Original languageEnglish
Pages (from-to)4329-4336
Number of pages8
JournalChemistry - A European Journal
Issue number14
Publication statusPublished - 2 Apr 2012


  • aromaticity; coordination chemistry; ligand design; N ligands; nitrogen heterocycles

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