Synthesis And Functionalization Of Xenon Binding Cryptophanes
Joseph, Akil I. E.
Joseph, Akil I. E.
To better understand the xenon binding properties of (±)-cryptophane-111 (111), crystals of its xenon and krypton complexes were prepared and analyzed by both single crystal and powder X-ray diffraction. The thermal stabilities of the different 111 crystalline phases were investigated by thermogravimetric analysis in tandem with mass spectrometry. A trigonal crystal form, Xe@111⋅y(solvent) was discovered to have outstanding thermal stability, sequestering xenon in the solid state to ~300 °C.To make 111 more amenable to functionalization, two new cryptophane-111 derivatives were synthesized, one bearing three methoxy moieties ((MeO)3-111) and the other six ((MeO)6-111) at the rim position. The methane binding and xenon binding properties of these 111 derivatives were also studied by 1H and 129Xe NMR spectroscopy. Their crystal structures were also obtained, including a xenon complex of the (MeO)3-111 derivative. The xenon complex is a highly compact complex with some of the shortest known Xe···C intermolecular contacts. The rim functionalization of 111 reduces the core conformational degrees of freedom perhaps counterintuitively resulting in a smaller cavity and a decreased affinity for both xenon and methane.A series of metalated cryptophanes were synthesized by affixing [(η5-C5Me5)RuII]+, ([Cp*RuII]+) moieties to the six arenes of several alkylenedioxy bridged cryptophanes, namely the cryptophanes-nmm (nmm = 111, 222, 223, 233, and 333), to make organometallic salts ([(Cp*Ru)6nmm]Cl6). These compounds are highly water-soluble. 129Xe NMR spectroscopy revealed very high xenon binding constants and also that the bound xenon signals of the permetalated cryptophanes (129Xe@[(Cp*Ru)6nmm]Cl6) resonate significantly downfield from their non-metalated versions (129Xe@nmm), thereby greatly expanding the chemical shift range of known 129Xe@cryptophane complexes. Additionally, crystal structures of various guest@[(Cp*Ru)6nmm]Cl6 were also determined.To further explore the deshielding effect of the [Cp*RuII]+ moieties on the encapsulated 129Xe NMR chemical shifts, partially metalated cryptophanes, [(Cp*Ru)x333]Clx and [(Cp*Ru)x111]Clx (1 ≤ x ≤ 5) were synthesized. The [(Cp*Ru)x333]Clx (1 ≤ x ≤ 5) derivatives were isolated, and characterized by 1H NMR spectroscopy (using their acetone@[(Cp*Ru)x333]Clx complexes) and electrospray ionization mass spectrometry. Partial metalation of the cryptophanes preserves the cryptophane core binding properties but allows for tuning of the chemical shift of the bound guests, which has tremendous potential for 129Xe NMR based sensing applications.
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