SCHIFF BASE MACROCYCLES: RELIABLE TEMPLATES FOR MULTINUCLEAR METALLOCAVITANDS

Abstract

Recent studies of polydentate Schiff base macrocycles indicate larger diameter macrocycles often deviate from planarity upon metal complexation, taking on a concave conformation. These bowl shaped complexes are reminiscent of organic cavitands, however, their dependence on metal coordination rather than C-C bonds for curvature has led us to dub them metallocavitands. In particular, we have prepared a family of soluble [3 + 3] Schiff base macrocycles from the condensation of 3,6-diformylcatechol with 1,2-dialkoxy-4,5-diaminobenzenes and investigated their ability to template the formation of metallocavitands. When reacted with seven equivalents of Zn(OAc)₂ or Cd(OAc)₂, hepta-nuclear metallocavitands are formed. Dimerization of these complexes into capsules has been observed and the thermodynamics of self-association has been studied. Tuning the cavity dimensions and strength of supramolecular self-association is easily achieved by switching metals. Isolation of a tetra-zinc intermediate has provided insight into the template effect our macrocycles exhibit. These results highlight the reliability of Schiff base macrocycles as scaffolds for metallocavitand formation.

Keywords:

• macrocycle
• metal cluster
• metallocavitand
• Schiff base
• supramolecular chemistry
• template

ACKNOWLEDGEMENTS

The authors are grateful to NSERC and UBC for funding our research on metallocavitands, and to the talented students who have worked on aspects of this chemistry, particularly Amanda Gallant and Jonathan Chong. We also thank Francesco Lelj for helpful discussions and computational studies.

Additional information

Notes on contributors

Peter D. Frischmann

Peter Frischmann completed a BSc at Idaho State University with Dr. Josh Pak in 2005. He is currently a PhD candidate with Dr. Mark MacLachlan at the University of British Columbia. His research is focused on the design and synthesis of new metal-containing supramolecular materials.

Mark J. MacLachlan

Mark J. MacLachlan is an associate professor of chemistry at the University of British Columbia. Previously, he completed his PhD at the University of Toronto with Ian Manners and Geoff Ozin, and worked as an NSERC Post-Doctoral Fellow with Timothy Swager at MIT. His research interests now include supramolecular scoordination chemistry and nanostructured materials.