Inclusion Complexation of Dimeric and Trimeric Oligo(ferrocenyldimethylsilanes) with γ-Cyclodextrin

Abstract

The oligo(ferrocenyldimethylsilanes) FcSiMe2Fc and FcSiMe2[(η5-C5H4)Fe(η5-C5H4SiMe2)]Fc [Fc = (η5-C5H5)Fe(η5-C5H4)] were encapsulated in γ-cyclodextrin (CD) to give crystalline inclusion compounds with 2:1 and 3:1 (host-to-guest) stoichiometries, respectively. A complex between γ-CD and ferrocene was also prepared for comparison. The formation of true inclusion complexes was confirmed in the solid state by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and 13C/29Si CP MAS NMR spectroscopy. Powder XRD reveals that the complexes containing ferrocene and the trimer 1,1‘-bis(ferrocenyldimethylsilyl)ferrocene have very similar solid-state structures based on channel-type packing of the host molecules. The complexes containing the oligo(ferrocenyldimethylsilanes) dehydrate up to 100 °C, after which no mass loss is registered by TGA in the temperature range 100−225 °C. The dissociation of the complexes occurs slightly above 225 °C and is immediately followed by the simultaneous release of the guests and the decomposition of the host in the temperature range 250−310 °C. 13C CP MAS NMR spectra of the inclusion compounds show that the encapsulation of the guest molecules in the CD cavity induces the host macrocycle to adopt a more symmetrical conformation, with each glucose unit in a more similar environment. The inclusion modes are discussed.