Self-selection in the self-assembly of isomeric supramolecular squares from unsymmetrical bis(4-pyridyl)acetylene ligands.
Liang Zhao, Brian H Northrop, Yao-Rong Zheng, Hai-Bo Yang, Hyo Jin Lee, Young Min Lee, Joo Yeon Park, Ki-Whan Chi, Peter J Stang
Index: J. Org. Chem. 73(17) , 6580-6, (2008)
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Abstract
A new approach wherein steric interactions between substituents of unsymmetrical bis(4-pyridyl)acetylene ligands dictate the self-selection of single isomers of [4 + 4] self-assembled squares is presented. Each [4 + 4] self-assembly is characterized by multinuclear (31)P and (1)H NMR spectroscopies and electrospray ionization mass spectrometry. NMR spectroscopic studies are used to provide a means of evaluating the efficiency of bulky substituents at proximal or remote positions relative to the Pt-N bonding motif to direct self-selection. Molecular modeling using the MMFF force field is utilized to determine the relative energy of different isomers of each assembly, and modeling results reasonably explain the trend in self-selectivity with varying pyridyl substitution.