Pillararenes are a new class of p-electron-rich macrocycles with a cylindrical structure composed of hydroquinone units connected by methylene bridges in their para positions. Recently, we have become interested in incorporating pillararenes into metal-organic frameworks (MOFs) to examine how electron-poor guests interact with the macrocyclic active domain of the material (Strutt, N.L. et. al., J. Am. Chem. Soc., 2012  , 134, 17436). A rigid organic strut with a pillar[5]arene (P5A) backbone has been synthesized, and P5A-MOF-1 was grown with Zn4O secondary building units (See Figure). P5A-MOF-1 was discovered to take up large quantities of electron-poor guests from solution, including nitroaromatics. A color change occurs in the crystal upon guest binding due to charge-transfer interactions between the encapsulated guest and the p-electron-rich cavity, indicating that P5A- MOF-1 may find application as a sensor for electron-deficient aromatics. The rigid difunctionalization of pillar[5]arene needed to create the organic strut imparts planar chirality onto the macrocycle. While a racemic modification was used to synthesize P5A-MOF-1, an enantiopure pillar[5]arene strut can be used to produce a homochiral version of P5A-MOF. A racemic modification of the strut has been resolved through the use of a chiral auxiliary protecting group. Upon deprotection, the synthesis of a homochiral version of P5A-MOF-1 was achieved. The structural properties of homochiral P5A-MOF are being studied along with its ability to act as a solid-phase support for the separation of small molecule racemates.

Novel porous materials utilizing pillararene macrocycles

246th National Meeting (2013)

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