Zinc(II) complexes with intramolecular amide oxygen coordination as models of metalloamidases

摘要

Polydentate ligands (6-R~1-2-pyridylmethyl)R~2(R~1= NHCOtBu, R~2= bis(2-pyridylmethyl)amine L~1, bis(2-(methylthio)ethyl)amine L~2 and N(CH_2CH_2)_2S L~3) form mononuclear zinc(II) complexes with intramolecular amide oxygen coordination and a range of coordination environments. Thus, the reaction of Zn(ClO_4)_2-H_2O with L~(1-3) in acetonitrile affords [(L)Zn](ClO_4)_2(L =L~1, 1; L_2, 2) and [(L_3)Zn(H_2O)(NCCH_3)](ClO_4)_(23). The simultaneous amide/water binding in 3 resembles the motif that has been proposed to be involved in the double substrateucleophile Lewis acidic activation and positioning mechanism of amide bond hydrolysis in metallopeptidases. X-ray diffraction, ~1H and ~(13)C NMR and IR data suggests that the strength of amide oxygen coordination follows the trend 1 > 2 > 3. L~(1-3) and 1-3 undergo cleavage of the tert-butylamide upon addition of Me4NOH?H2O (1 equiv.) in methanol at 50(1) ℃. The rate of amide cleavage follows the order 1 > 23, L~(1-3). The extent by which the amide cleavage reaction is accelerated in 1-3 relative to the free ligands, L~(1-3), is correlated with the strength of amide oxygen binding and Lewis acidity of the zinc(II) centre in 1-3 deduced from the X-ray, NMR and IR studies.