title: Enantiomerization of chiral uranyl-salophen complexes via unprecedented ligand hemilability: toward configurationally stable derivatives.
abstract: In the search for configurationally stable inherently chiral uranyl-salophen complexes, the newly synthesized compound 3 featuring a dodecamethylene chain was expected to be a promising candidate. Unexpectedly, dynamic HPLC on a enantioselective column showed that it still undergoes enantiomerization at high temperature. By comparison with the dynamic behavior of compounds 4 and 5, it was found that the enantiomerization rate is independent of the size of the ligand. This finding definitely rules out a jump rope-type mechanism for the enantiomerization process and points to reaction pathways involving preliminary rupture of one of the O...U coordinative bonds. This provides unprecedented evidence of the occurrence of ligand hemilability in metal-sal(oph)en complexes. Such findings inspired the synthesis of compound 6 endowed with a more rigid spacer, i.e., that derived from 4,4'-(1,4-phenylenediisopropylidene)bisphenol. DHPLC investigations showed that the new structural motif imparts a higher configurational stability, thus raising the half-life for the enantiomerization to more than 2 months at room temperature. This clearly establishes that this compound represents the first member of a new class of inherently chiral receptors, whose potential in chiral recognition and catalysis now can be feasibly explored.
authors.affiliation: Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Universita La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Ciogli
authors.forename: Antonella
authors.initials: A
authors.lastname: Dalla Cort
authors.forename: Francesco
authors.initials: F
authors.lastname: Gasparrini
authors.forename: Lodovico
authors.initials: L
authors.lastname: Lunazzi
authors.forename: Luigi
authors.initials: L
authors.lastname: Mandolini
authors.forename: Andrea
authors.initials: A
authors.lastname: Mazzanti
authors.forename: Chiara
authors.initials: C
authors.lastname: Pasquini
authors.forename: Marco
authors.initials: M
authors.lastname: Pierini
authors.forename: Luca
authors.initials: L
authors.lastname: Schiaffino
authors.forename: Francesco Yafteh
authors.initials: FY
authors.lastname: Mihan