Encapsulation of catalytically active transition metal complexes (TMCs) by larger cavitands gives rise to novel supramolecular catalysts, where the cavitand acts as an actual molecular vessel:1 these species’ regioselectivity may be conveniently tuned by altering chirality in their outer regions, rather than by direct intervention on their encapsulated TMC guest. Moreover, encapsulation may protect a TMC, enhance its catalytic efficiency, and even introduce entirely new catalytic properties altogether. Ballester, Bo, and collaborators have in recent years successfully combined NMR spectroscopy and DFT to study several catalytic TMCs2-4 enclosed in Rebek’s cavitand 15—a resorcin[4]arene functionalised with 8 octaamide moieties. In this communication, we provide insight on the unique behaviour of another TMC confined within 1: [Ir(THF)2(COD)]+@1 (2+@1; THF = tetrahydrofuran; COD = 1,5-cyclooctadiene). NMR results have indicated that inside 1, 2+ adopts a peculiarly hindered axial rotation, slow enough to be detected at 273 K. Intrigued by these findings, we corroborate them with a series of DFT calculations on 2+@1, mapping a 90°-portion of 2+’s rotation within the host: indeed, we identify a complex energetic landscape, fraught with barriers, entirely compatible with NMR observations. (1) Leenders, S. H. A. M.; Gramage-Doria, R.; de Bruin, B.; Reek, J. N. H. Chem. Soc. Rev. 2015, 44, 433-448. (2) Hamilton, A.; Gicquel, M.; Ballester, P.; Bo, C. Curr. Org. Chem. 2013, 17, 1499-1506. (3) Sarmentero, M. A.; Fernández-Pérez, H.; Zuidema, E.; Bo, C.; Vidal-Ferran, A.; Ballester, P. Angew. Chem., Int. Ed. 2010, 49, 7489-7492. (4) Zuidema, E.; Sarmentero, M. A.; Bo, C.; Ballester, P. Chem. – Eur. J. 2008, 14, 7285-7295. (5) Rudkevich, D. M.; Hilmersson, G.; Rebek, J. J. Am. Chem. Soc. 1997, 119, 9911-9912.

Supramolecular rotation: The fascinating motion of an IrI complex within Rebek’s self-folding octaamide cavitand

251st National Meeting (2016)

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