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Kinetic and Thermodynamic Stabilization of Metal Complexes by Introverted Coordination in a Calix[6]azacryptand
Author(s) -
Inthasot Alex,
Brunetti Emilio,
Lejeune Manuel,
Menard Nicolas,
Prangé Thierry,
Fusaro Luca,
Bruylants Gilles,
Reinaud Olivia,
Luhmer Michel,
Jabin Ivan,
Colasson Benoit
Publication year - 2016
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.201505057
Subject(s) - chemistry , ligand (biochemistry) , supramolecular chemistry , calixarene , coordination sphere , azide , transmetalation , metal , metal ions in aqueous solution , selectivity , polymer chemistry , crystallography , coordination complex , amine gas treating , stereochemistry , crystal structure , organic chemistry , molecule , catalysis , receptor , biochemistry
The Huisgen thermal reaction between an organic azide and an acetylene was employed for the selective monofunctionalization of a X 6 ‐azacryptand ligand bearing a tren coordinating unit [X 6 stands for calix[6]arene and tren for tris(2‐aminoethyl)amine]. Supramolecular assistance, originating from the formation of a host–guest inclusion complex between the reactants, greatly accelerates the reaction while self‐inhibition affords a remarkable selectivity. The new ligand possesses a single amino‐leg appended at the large rim of the calixarene core and the corresponding Zn 2+ complex was characterized both in solution and in the solid state. The coordination of Zn 2+ not only involves the tren cap but also the introverted amino‐leg, which locks the metal ion in the cavity. Compared with the parent ligand deprived of the amino‐leg, the affinity of the new monofunctionalized X 6 tren ligand 6 for Zn 2+ is found to have a 10‐fold increase in DMSO, which is a very competitive solvent, and with an enhancement of at least three orders of magnitude in CDCl 3 /CD 3 OD (1:1, v/v). In strong contrast with the fast binding kinetics, decoordination of Zn 2+ as well as transmetallation appeared to be very slow processes. The monofunctionalized X 6 tren ligand 6 fully protects the metal ion from the external medium thanks to the combination of a cavity and a closed coordination sphere, leading to greater thermodynamic and kinetic stabilities.