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Large p K a Shifts of α‐Carbon Acids Induced by Copper( II ) Complexes
Author(s) -
Zhong Zhenlin,
Postnikova Brenda J.,
Hanes Robert E.,
Lynch Vincent M.,
Anslyn Eric V.
Publication year - 2005
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.200400396
Subject(s) - copper , chemistry , acetonitrile , methylene , ion , metal , carbon fibers , inorganic chemistry , hydrogen bond , hydrogen , molecule , stereochemistry , medicinal chemistry , crystallography , organic chemistry , materials science , composite number , composite material
A series of synthetic receptors ( 4 – 6 ) incorporating metal ions, specifically copper( II ), were examined for their ability to enhance the acidity of active methylene compounds. The copper( II ) complexes were observed to reduce the p K a of 1,3‐diketone carbon acids in acetonitrile by as much as 12 p K a units. The relatively large p K a reduction achieved by the complex is attributed to the electrostatic interaction between the anionic π system of the enolate and the copper( II ) ions. The cage structure and hydrogen bonding sites in receptors 4 and 5 lead to a very modest further enhancement of the acidity relative to that with 6 . This study provides insight into the way in which metalloenzymes stabilize an enolate intermediate.