Cucurbit[7]uril⋅Guest Pair with an Attomolar Dissociation Constant

Host?guest complexes between cucurbit[7] (CB[7]) or CB[8] and diamantane diammonium ion guests 3 or 6 were studied by ¹H NMR spectroscopy and X‐ray crystallography. ¹H NMR competition experiments revealed that CB[7]? 6 is among the tightest monovalent non‐covalent complexes ever reported in water with K_a=7.2×10¹⁷ M ^?1 in pure D₂O and 1.9×10¹⁵ M ^?1 in D₂O buffered with NaO₂CCD₃ (50 mM ). The crystal structure of CB[7]? 6 allowed us to identify some of the structural features responsible for the ultratight binding, including the distance between the NMe₃⁺ groups of 6 (7.78 Å), which allows it to establish 14 optimal ion‐dipole interactions with CB[7], the complementarity of the convex van der Waals surface contours of 6 with the corresponding concave surfaces of CB[7], desolvation of the C?O portals within the CB[7]? 6 complex, and the co‐linearity of the C₇ axis of CB[7] with the N⁺???N⁺ line in 6 . This work further blurs the lines of distinction between natural and synthetic receptors.     

Reactions at high pressure 13; volume profiles for the brominolyses of tetra-alkylstannanes.

Volumes of activation and of reaction have been measured for the S_E2 brominolyses in cyclohexane of SnR₄, R= Et,1-Bu and 2-Bu and lie in the range, respectively ?50 to ?60 and +20 to +35 cm³mol^?1.     

Blurring the Lines between Host and Guest: A Chimeric Receptor Derived from Cucurbituril and Triptycene

We report the synthesis and X‐ray crystal structure of a cucurbituril–triptycene chimeric receptor ( 1 ). Host 1 binds to guests typical of CB[6]–CB[8], but also binds to larger guests such as blue box ( 20 ) and the Fujita square ( 22 ). Intriguingly, the geometries of the 1 ? 20 and 1 ? 22 complexes blur the lines between host and guest in that both components fulfill both roles within each complex. The fluorescence output of 1 is fully quenched by the formation of complexes with pyridinium‐derived guests.     

Group V complexes of the tricarbonyl(η-cycloheptatrienylium)molybdenum cation and their reduction to monosubstituted derivatives of tricarbonyl(1-6-η-cycloheptatriene)molybdenum

Reaction of [(η-C₇H₇)Mo(CO)₃][PF₆] with certain Group V donor ligands afforded monosubstituted complexes [(η-C₇H₇)Mo(CO)₂L][PF₆] (L = P(OPh)₃, PPh₃, PPh₂Me, PPhMe₂, AsPh₃, SbPh₃). These were reduced by NaBH₄ to the corresponding cycloheptatriene complexes (1-6-η-C₇H₈)Mo(CO)₂L. In addition, the preparation of alkylcycloheptatriene complexes (1-6-η-C₇H₇R)Mo(CO)₂L (R = Me, L = P(OPh)₃, PPh₃, PPh₂Me; R = t-Bu, L = PPh₃) is described. Spectroscopic properties, including ¹³C NMR, are reported.     

The cucurbit[n]uril family: prime components for self-sorting systems

We determined the values of Ka for a wide range of host-guest complexes of cucurbit[n]uril (CB[n]), where n = 6-8, using 1H NMR competition experiments referenced to absolute binding constants measured by UV/vis titration. We find that the larger homologues--CB[7] and CB[8]--individually maintain the size, shape, and functional group selectivity that typifies the recognition behavior of CB[6]. The cavity of CB[7] is found to effectively host trimethylsilyl groups. Remarkably, the values of Ka for the interaction of CB[7] with adamantane derivatives 22-24 exceeds 10(12) M(-1)! The high levels of selectivity observed for each CB[n] individually is also observed for the CB[n] family collectively. That is, the selectivities of CB[6], CB[7], and CB[8] toward a common guest can be remarkably large. For example, guests 1, 3, and 11 prefer CB[8] relative to CB[7] by factors greater than 10(7), 10(6), and 3000, respectively. Conversely, guests 23 and 24 prefer CB[7] relative to CB[8] by factors greater than 5100 and 990, respectively. The high levels of selectivity observed individually and collectively for the CB[n] family renders them prime components for the preparation of functional biomimetic self-sorting systems.