Title
Chiroptical Inversion of Europium(III) Complexes by Changing a Remote Stereogenic Center of a C2-Symmetric Bispyrrolidinoindoline Manifold
Author
Tomoaki Taniguchi, Akira Tsubouchi, Yuki Imai, Junpei Yuasa, Hiroki Oguri
Year
2018
Journal
The Journal of Organic Chemistry
Abstract
As an effort to integrate natural products chemistry and coordination chemistry, a diastereomeric pair of chiral alkaloidal manifolds composed of a bispyrrolidinoindoline (BPI) framework was designed and synthesized to generate luminescent EuIII complexes with switchable chiroptical properties. The C2-symmetric alkaloidal manifolds were linked with bis(benzimidazolyl)pyridine (BBIPy) as an achiral metal-binding component through substituents installed at the stereogenic 2/2′ positions of the BPI manifolds. The resulting diastereomeric pair of ligands, syn-L1 and anti-L2, allow pseudomirror symmetrical presentation of the metal-binding BBIPy units due to the stereogenic centers on the alkaloidal manifold. The ligand syn-L1 induces intramolecular coordination to form the 1:1 complex EuIII(syn-L1) composed of a single stranded metal helicate which exhibits a negative split Cotton effect. In contrast, the ligand anti-L2 led to a supramolecular assembly comprising the 2:2 complex EuIII2(anti-L2)2 consisting of a bimetallic double-stranded helicate which shows a positive split Cotton effect. Thus, the sp3 stereogenic centers in the BPI manifolds play pivotal roles in controlling both metal–ligand equilibria and chirality-switching of luminescent EuIII complexes. This approach, which exploits diastereomeric natural product-based manifolds, provides a relatively unexplored means for diversifying metal coordination modes and for controlling the chiroptical properties of the resultant luminescent lanthanoid complexes.
Full Article
Instrument
J-815, FP-6500, V-630
Keywords
Circular dichroism, Stereochemistry, Cotton effect, Chemical stability, Ligand binding, Coordination chemistry, Inorganic chemistry, Fluorescence, Photoluminescence, Quenching