Towards Multi-generation Assemblies with Tetraphenylmethane Subunits

Abstract

The synthesis of tetra(4-hydroxymethylphenyl)methane is reported. Possessing four benzyl alcohol groups, this molecule is anticipated to undergo self-assembly processes analogous to previously studied benzyl alcohol derived, deep-cavity cavitands (Gibb, C. L. D.; Stevens, E. D.; Gibb, B. C. Chem. Commun. 2000, 363–364). Towards such assembly processes, a bis-protected derivative was synthesized and its ability to undergo a macrocyclization reaction determined. Both the protection strategy employed and the macrocyclization approach are important models for more complex, repetitive self-assembly processes that can be envisaged with these types of molecules.

Abstract

Synthesis of tetraphenylmethane subunit 3. Conditions are: (a) Ph²Zn, -42°C, CH²Cl²; (b) I²/bis(trifluoroacetoxy)-iodobenzene in CCl⁴; (c) n-BuLi -78°C, then -30°C, then -78°C, then dimethylformamide; (d) NaBH⁴.

Reaction of model compounds 7 and 8.

Products from the reaction of model 9 under the standard “assembly” conditions.

Synthesis of protected subunits 12 and 13.

Synthesis of second-generation subunit 16.

Keywords:

• Macrocyclization
• Self-assembly

Acknowledgements

This work was supported by the National Science Foundation (CHE-0111133) and The Petroleum Research Fund administered by the American Chemical Society.

Notes

The Future of Supramolecular ChemistrySupramolecular chemistry is still in its formative years. On the (180-year) organic synthesis scale, we are somewhere in between Kolbe's synthesis of acetic acid (1845), and Fischer's synthesis of glucose (1890). With more researchers and more powerful tools at our disposal, imagine where the supramolecular community can be after 180 years! At some point between now and then, our level of understanding of how to position and orchestrate functionality within molecules will have progressed to the point that synthetic chemists will have more than just natural products to aim for. These include, but are by no means limited to: synthetic and natural polymers with fully controllable secondary, tertiary and quaternary structures that will open the way to artificial viral capsids for gene therapy and drug delivery; the synthetic equivalents of complex biological matrices possessing molecular detectors, triggers, and switchable, multifaceted catalysts that make modern-day reagents look crude and unspecific; crystalline solids that adsorb species for storage, or release selected compounds upon specific stimulus; memory materials, self-repairing materials, molecular machines and molecular computers. The list goes on. Self-assembly, in a chemical sense the spontaneous creation of supramolecular patterns or order, offers an efficient way to access many of the aforementioned new materials. This ultimate antithesis to entropy has made many advances over the last few years. As a result, nascent frameworks that can be used to identify, characterize, and categorize assembly processes are emerging. Much, however, still remains to be done; both in a conceptual sense and in an empirical sense. Our small contribution presented here pertains to the latter.Bruce C. Gibb is currently an Associate Professor of Chemistry at the University of New Orleans. His research interests focus on supramolecular chemistry, with a decided tilt towards the organic and bioorganic. He received his undergraduate education at The Robert Gordon's University (Aberdeen, Scotland), and remained there to carry out his PhD studies under the guidance of Philip J. Cox. Shortly thereafter, in 1993, he moved to the University of British Columbia where he carried out postdoctoral research with Professor John C. Sherman. In 1994, he undertook a second period of postdoctoral research, this time with James W. Canary at New York University. Most recently, in 1996, he took up an appointment as an Assistant Professor at the University of New Orleans.