Chiroptical Inversion of Europium(III) Complexes by Changing a Remote Stereogenic Center of a C₂-Symmetric Bispyrrolidinoindoline Manifold

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 Eu III complexes with switchable chiroptical properties. The C 2 -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 Eu III (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 Eu III 2 (anti-L2) 2 consisting of a bimetallic double-stranded helicate which shows a positive split Cotton effect. Thus, the sp 3 stereogenic centers in the BPI manifolds play pivotal roles in controlling both metal−ligand equilibria and chiralityswitching of luminescent Eu III 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.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

“…The stereogenic center in BPI led to different spatial arrangements of the metal-binding sites. Upon coordinating with Ln III ions, chiral mononuclear Eu­( syn - 168 ) and bimetallic helicate Eu 2 ( anti - 168 ) 2 were formed, respectively, which showed pseudo enantiomeric chiral optical performances . Despite the relatively long distance between the stereogenic centers and the coordinating sites, the chirality was transferred to the Ln III center and resulted in chiral luminescent Ln III complexes.…”

Strategies for total synthesis of bispyrrolidinoindoline alkaloids

“…An alternative catalytic dimerization has been carried out by Oguri with Mn as the reductant and DPPBz as the ligand (method B). 89 Sequential transformations following widely adopted procedures afforded racemic chimonanthine and folicanthine. Peng further extended the Ni 0 -catalyzed dimerization to the total synthesis of (−)-folicanthine ( 13 ) and (−)-ditryptophenaline ( 21 ) by using Phen as the ligand.…”

“…Instead, Oguri discovered that the coupling yield was significantly improved by using Mn as the reductant that guaranteed the stereo-divergent synthesis of BPI analogues for stereospecific antiproliferative activity. 91…”

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes

“…Chiral sorting corresponds to enantiomeric self-recognition or enantiomeric self-discrimination, and these processes have been documented for supramolecular systems, − metal complexes, − and organic systems, including macrocyclic compounds. − Chiral sorting phenomena are most often demonstrated for solid state, while examples of enantiomeric self-recognition well documented for solutions of metal complexes are less common. Another important issue in the synthesis of elaborate enantiopure metal complexes or supramolecular assemblies is chirality transfer, − e.g., the transmission of chiral information from enantiopure ligands to metal centers. While there are many chiral transition metal complexes with well-defined stable configurations, the control over chirality of lanthanide complexes, in particular polynuclear complexes, − ,− is more difficult due to the lack of spatial preferences, lability, and high-coordination numbers of these ions.…”