Hydrogen bonds in metalloproteins are key in directing reactivity yet to be achieved in synthetic systems. We have been developing a synthetic system that uses hydrogen-bonding interactions to modulate the secondary coordination around a transition metal ion. This was accomplished with the ligand bis[N-(6-pivalamido-2-pyridylmethyl)]benzylamine (H2pmb), which contains two carboxyamido units appended from pyridine rings. Several nickel complexes were prepared and structurally characterized. In particular, we found that the appended carboxyamido groups either provide intramolecular H-bond donors or can be converted to bind directly to a metal center. We established that the complex NiIIH2pmb(Cl)2 can be sequentially deprotonated with potassium tert-butoxide, causing coordination of the carboxyamido oxygen atoms and concomitant loss of the chloro ligands. The chloro ligands were also removed with silver(I) salts—in the presence of acetate ions, the complex NiIIH2pmb(κ2-OAc)(κ1-OAc) was isolated, in which an intramolecular H-bonding network occurs between the H2pmb ligand and the coordinate acetato ligands.
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