Robust Chiral Nanostructures: Global Chirality in Supramolecules Constructed from Enantiopure Ruthenium(II) Trisdiimine Building Blocks

Abstract

One hallmark of supramolecular chemistry is the spatial organization of the individual components with respect to one another over nanoscopic distances. Frequently, coordination complexes play an important role in such systems, however, few are robust or inert enough to withstand a significant amount of physical or chemical manipulation. One exception is supramolecular structures constructed from enantiomerically pure [Ru(phenanthroline)₃]²⁺ complexes. When bridged by rigid, planar aromatic tpphz ligands (tpphz = tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2″,3″j]phenazine), these complexes form robust, structurally rigid and well-defined, nanoscopic complexes. A series of enantiomerically and diastereomerically pure ruthenium(II) dimers, tetramers, hexamers, decamers and linear polymers have been prepared using a stereospecific synthetic strategy involving the coupling reaction between peripheral ortho-diamine and orthoquinone groups. These structures show spatial organization over nanoscopic distances with diameters ranging from 1.6 nm to over 5.0 nm. Due to the overall rigidity, the global structure of these molecules is easily modeled and shown to differ dramatically for different diastereomers. Most importantly, this system presents a synthetic approach to tailorable, robust and even chiral nanoscopic structures which exhibit unique physical properties and may serve as platforms for even larger mesoscopic architectures. Because of the unique kind stereoisomerism present in these topologically different diastereomers, the term atopomers is introduced to describe their stereochemistry. These structures also show a global chirality or chiral tertiary structure which is classified by the stereochemical descriptors P, M and T, as defined herein.

Key Words:

• chirality
• topochimistry
• Stereochemistry
• ruthenium
• polypryudyl ligands
• supramolecular atopomer