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Charged Behaviour from Neutral Ligands: Synthesis and Properties of N‐Heterocyclic Pseudo‐amides
Author(s) -
Thatcher Robert J.,
Johnson David G.,
Slattery John M.,
Douthwaite Richard E.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201103319
Subject(s) - chemistry , deprotonation , pyridinium , ligand (biochemistry) , amide , alkyl , stereochemistry , substituent , isopropyl , zwitterion , resonance (particle physics) , iodide , crystallography , molecule , medicinal chemistry , ion , organic chemistry , biochemistry , physics , receptor , particle physics
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 metal–ligand 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 CN 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 CC 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.