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Activation of Oximic Nucleophiles by Coordination of Transition Metal Ions
Author(s) -
Mancin Fabrizio,
Tecilla Paolo,
Tonellato Umberto
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(200003)2000:6<1045::aid-ejoc1045>3.0.co;2-m
Subject(s) - chemistry , reactivity (psychology) , nucleophile , ligand (biochemistry) , metal , medicinal chemistry , stereochemistry , transition metal , cleavage (geology) , metal ions in aqueous solution , reaction rate constant , kinetics , inorganic chemistry , organic chemistry , catalysis , medicine , biochemistry , alternative medicine , receptor , geotechnical engineering , pathology , fracture (geology) , engineering , physics , quantum mechanics
A kinetic study of the reactivity in the cleavage of p ‐nitrophenyl acetate of a series of 2‐pyridineoximes, 1 ‐ 4 , and their complexes with Ni II , Zn II and Cu II is reported. Complexation of the oximic ligands leads to a remarkable increase in the acidity of the oximic group, following the order Cu II > Ni II > Zn II . The oximates of free ligands and their metal complexes, being α‐nucleophiles, are quite effective in promoting the cleavage of PNPA. However, the reactivity, as defined by the second‐order rate constants, is not predictably related to the acidity of the oximic function. The corresponding Brønsted plot shows a linear behaviour up to a p K a value of ca. 8, above which the reactivity of the uncomplexed oximic functions levels off to a limiting value. In the case of the metal ion complexes, a large effect of the ligand structure on the reactivity was observed. As a consequence, complexes of appropriate ligands and metal ions show a reactivity that exceeds the apparent limiting one of the oximates. The origin of such effects and their possible implications in the development of new reactivators of phosphorylated acetylcholinesterase are discussed.