Vernier-Templated Synthesis, Crystal Structure, and Supramolecular Chemistry of a 12-Porphyrin Nanoring

• Published in: Chemistry : a European journal Vol. 20; no. 40; pp. 12826 - 12834
• Main Authors: Kondratuk, Dmitry V., Sprafke, Johannes K., O'Sullivan, Melanie C., Perdigao, Luis M. A., Saywell, Alex, Malfois, Marc, O'Shea, James N., Beton, Peter H., Thompson, Amber L., Anderson, Harry L.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 26.09.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Binding sites; Chemistry; conjugation; Crystal structure; Deposition; Displays; macrocycles; Nanostructure; porphyrinoids; Scanning tunneling microscopy; supramolecular chemistry; Synthesis; Synthesis (chemistry); template synthesis; porphyrinoids; template synthesis; macrocycles; conjugation; supramolecular chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201403714

Vernier templating exploits a mismatch between the number of binding sites in a template and a reactant to direct the formation of a product that is large enough to bind several template units. Here, we present a detailed study of the Vernier‐templated synthesis of a 12‐porphyrin nanoring. NMR and small‐angle X‐ray scattering (SAXS) analyses show that Vernier complexes are formed as intermediates in the cyclo‐oligomerization reaction. UV/Vis/NIR titrations show that the three‐component assembly of the 12‐porphyrin nanoring figure‐of‐eight template complex displays high allosteric cooperativity and chelate cooperativity. This nanoring–template 1:2 complex is among the largest synthetic molecules to have been characterized by single‐crystal analysis. It crystallizes as a racemate, with an angle of 27° between the planes of the two template units. The crystal structure reveals many unexpected intramolecular CH⋅⋅⋅N contacts involving the tert‐butyl side chains. Scanning tunneling microscopy (STM) experiments show that molecules of the 12‐porphyrin template complex can remain intact on the gold surface, although the majority of the material unfolds into the free nanoring during electrospray deposition. Two templates work together: When one template does not fit inside a target macrocycle, two can do the trick (see figure). The synthesis and crystal structure of this giant 12‐porphyrin macrocycle bound to two templates has generated new insights into possibilities for template‐directed synthesis.