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 impartsa 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.
Enantiomerization of Chiral Uranyl-Salophen Complexes via Unprecedented Ligand Hemilability. TowardsConfigurationally Stable Derivatives / A. Ciogli; A. Dalla Cort; F. Gasparrini; L. Lunazzi; L. Mandolini; A. Mazzanti; C. Pasquini; M. Pierini; L. Schiaffino; F. Yafteh Mihan. - In: JOURNAL OF ORGANIC CHEMISTRY. - ISSN 0022-3263. - STAMPA. - 73:(2008), pp. 6108-6118. [10.1021/jo800610f]
Enantiomerization of Chiral Uranyl-Salophen Complexes via Unprecedented Ligand Hemilability. TowardsConfigurationally Stable Derivatives
LUNAZZI, LODOVICO;MAZZANTI, ANDREA;
2008
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 impartsa 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.