Capsule Formation, Carboxylate Exchange, and DFT Exploration of Cadmium Cluster Metallocavitands: Highly Dynamic Supramolecules Peter D. Frischmann, † Glenn A. Facey, ‡ Phuong Y. Ghi, ‡ Amanda J. Gallant, † David L. Bryce,* ,‡ Francesco Lelj,* ,§ and Mark J. MacLachlan* ,† Department of Chemistry, UniVersity of British Columbia, 2036 Main Mall, VancouVer, British Columbia V6T 1Z1, Canada, Department of Chemistry and Centre for Catalysis Research and InnoVation, UniVersity of Ottawa, D’Iorio Hall, 10 Marie Curie PVt., Ottawa, Ontario K1N 6N5, Canada, and La.M.I. and LaSSCAM INSTM Sezione Basilicata, Dipartimento di Chimica, UniVersita ` della Basilicata, Via N. Sauro 85, 85100 Potenza, Italy Received December 14, 2009; E-mail: mmaclach@chem.ubc.ca; david.bryce@uottawa.ca; francesco.lelj@unibas.it Abstract: A family of molecular heptacadmium carboxylate clusters templated inside [3 + 3] Schiff base macrocycles has been isolated and studied by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. These metallocavitand cluster complexes adopt bowl-shaped structures, induced by metal coordination, giving rise to interesting host-guest and supramolecular phenomena. Specifically, dimerization of these metallocavitands yields capsules with vacant coordination and hydrogen-bonding sites accessible to encapsulated guests. Strong host-guest interactions explain the exceptionally high packing coefficient (0.80) observed for encapsulated N,N-dimethylformamide (DMF). The guest-accessible hydrogen-bonding sites arise from an unusual µ 3 -OH ligand bridging three cadmium ions. Thermodynamic and kinetic studies show that dimerization is an entropy-driven process with a highly associative mechanism. In DMF the exchange rate of peripheral cluster supporting carboxylate ligands is intrinsically linked to the rate of dimerization and these two seemingly different events have a common rate-determining step. Investigation of guest dynamics with solid-state 2 H NMR spectroscopy revealed 3-fold rotation of an encapsulated DMF molecule. These studies provide a solid understanding of the host-guest and dynamic properties of a new family of metallocavitands and may help in designing new supramolecular catalysts and materials. Introduction The ability to selectively confine metal clusters to desired size domains helped usher in the age of nanoscience, giving rise to materials with exceptional novelty. 1 Besides numerous materials science applications, 2 synthesis of molecular metal clusters is paramount in the design of multimetallic catalysts 3 and enzyme mimics. 4 Template-directed or aggregation-based synthetic approaches are most often employed to access complex multimetallic clusters. 5 For example, both approaches have been used to synthesize models of the Fe 7 Mo cofactor in nitrogenase enzymes, a highly sought after complex for elucidating the mechanism of nitrogen fixation. 4,6 Metal clusters mimicking enzyme active sites as well as nonbiological systems have proven to be powerful catalysts, allowing or accelerating a † University of British Columbia. ‡ University of Ottawa. § Universita ` della Basilicata. (1) (a) Ozin, G. A.; Arsenault, A. C. Nanochemistry; Royal Society of Chemistry: Cambridge, 2005. (b) Ozin, G. A. AdV. Mater. 1992, 4, 612–649. (2) (a) Mezei, G.; Zaleski, C. M.; Pecoraro, V. L. Chem. ReV. 2007, 107, 4933–5003. (b) Brechin, E. K. Chem. Commun. 2005, 5141–5153. (c) Christou, G.; Gatteschi, D.; Hendrickson, D. N.; Sessoli, R. MRS Bull. 2000, 25, 66–71. (3) Shibasaki, M., Yamamoto, Y., Eds.; Multimetallic Catalysts in Organic Synthesis; Wiley-VCH: Weinheim, Germany, 2004. (4) (a) Ohki, Y.; Ikagawa, Y.; Tatsumi, K. J. Am. Chem. Soc. 2007, 129, 10457–10465. (b) Laplaza, C. E.; Holm, R. H. J. Am. Chem. Soc. 2001, 123, 10255–10264. (5) Recent examples: (a) Feltham, H. L. C.; Brooker, S. Coord. Chem. ReV. 2009, 253, 1458–1475. (b) Lan, Y.; Novitchi, G.; Cle ´rac, R.; Tang, J.-K.; Madhu, N. T.; Hewitt, I. J.; Anson, C. E.; Brooker, S.; Powell, A. K. Dalton Trans. 2009, 1721–1727. (c) Kleij, A. W. Chem.sEur. J. 2008, 14, 10520–10529. (d) Niel, V.; Milway, V. A.; Dawe, L. N.; Grove, H.; Tandon, S. S.; Abedin, T. S. M.; Kelly, T. L.; Spencer, E. C.; Howard, J. A. K.; Collins, J. L.; Miller, D. O.; Thompson, L. K. Inorg. Chem. 2008, 47, 176–189. (e) Schemberg, J.; Schneider, K.; Demmer, U.; Warkentin, E.; Mu ¨ller; Ermler, U. Angew. Chem., Int. Ed. 2007, 46, 2408–2413. (f) Nabeshima, T.; Miyazaki, H.; Iwasaki, A.; Akine, S.; Saiki, T.; Ikeda, C. Tetrahedron 2007, 63, 3328–3333. (g) Zheng, N.; Lu, H.; Bu, X.; Feng, P. J. Am. Chem. Soc. 2006, 128, 4528–4529. (h) Artuso, F.; D’Archivio, A. A.; Lora, S.; Jerabek, K.; Kra ´lik, M.; Corain, B. Chem.sEur. J. 2003, 9, 5292–5296. (i) Aromı ´, G.; Gamez, P.; Roubeau, O.; Kooijman, H.; Spek, A. L.; Driessen, W. L.; Reedijk, J. Angew. Chem., Int. Ed. 2002, 41, 1168–1170. (j) Fontecha, J. B.; Goetz, S.; McKee, V. Angew. Chem., Int. Ed. 2002, 41, 4553–4556. (k) Che, C.-M.; Xia, B.-H.; Huang, J.-S.; Chan, C.-K.; Zhou, Z.-Y.; Cheung, K.-K. Chem.sEur. J. 2001, 7, 3998–4006. (l) Laplaza, C. E.; Holm, R. H. J. Am. Chem. Soc. 2001, 123, 10255–10264. (m) Doble, D. M. J.; Benison, C. H.; Blake, A. J.; Fenske, D.; Jackson, M. S.; Kay, R. D.; Li, W.-S.; Schro ¨der, M. Angew. Chem., Int. Ed. 1999, 38, 1915–1918. (6) Einsle, O.; Tezcan, F. A.; Andrade, S. L. A.; Schmid, B.; Yoshida, M.; Howard, J. B.; Rees, D. C. Science 2002, 297, 1696–1700. Published on Web 03/02/2010 10.1021/ja910419h  2010 American Chemical Society J. AM. CHEM. SOC. 2010, 132, 3893–3908 9 3893