Premium
Biomimetic Copper( I )–CO Complexes: A Structural and Dynamic Study of a Calix[6]arene‐Based Supramolecular System
Author(s) -
Rondelez Yannick,
Sénèque Olivier,
Rager MarieNoëlle,
Duprat Arthur F.,
Reinaud Olivia
Publication year - 2000
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 - 10.1002/1521-3765(20001117)6:22<4218::aid-chem4218>3.0.co;2-v
Subject(s) - supramolecular chemistry , steric effects , chemistry , crystallography , imidazole , calixarene , stereochemistry , nmr spectra database , molecule , crystal structure , spectral line , organic chemistry , physics , astronomy
Four novel calix[6]arene‐based cuprous complexes are described. They present a biomimetic tris(imidazole) coordination core associated with a hydrophobic cavity that wraps the apical binding site. Each differs from the other by the methyl or ethyl substituents present on the phenoxyl groups (OR 1 ) and on the imidazole arms (NR 2 ) of the calix[6]arene structure. In solution, stable CO complexes were obtained. We have investigated their geometrical and dynamic properties with respect to the steric demand. IR and NMR studies revealed that, in solution, these complexes adopted two distinct conformations. The preferred conformation was dictated only by the size of the OR 1 group. When R 1 was an ethyl group, the complex preferentially adopted a flattened C 3 ‐symmetrical structure. The corresponding helical enantiomers were in conformational equilibrium, which, however, was slow on the 1 H NMR time scale at −80 °C. When R 1 was a methyl group, the low‐temperature NMR spectra revealed the partial inclusion of one t Bu group. The complex wobbled between three dissymmetric but equivalent conformations. Hence, small differences in the steric demand of the calixarene's skeleton changed the geometry and dynamics of the system. Indeed, this supramolecular control was promoted by the strong conformational coupling between the metal center and the host structure. Interestingly, this was not only the result of a covalent preorganization, but also stemmed from weak interactions within the hydrophobic pocket. The vibrational spectra of the bound CO were revealed to be a sensitive gauge of this supramolecular behavior, similar to copper proteins in which allosteric effects are common.