ABSTRACT
Bambusuril macrocycles have high affinity towards anions (X-) such as PF6- and SbF6- or BF4- and ClO4-. Therefore, addition of bambusurils to reaction mixtures containing these anions effectively removes the free anions from the reaction process. Hence, comparing reactions with and without addition of bambusurils can demonstrate whether the anions actively participate in the reaction mechanism or not. We show this approach for gold(i) mediated addition of methanol to an alkyne. The reaction mechanism can proceed via monoaurated intermediates (e.g., in catalysis with [(IPr)AuX]) or via diaurated intermediates (e.g., in catalysis with [(PPh3)AuX]). We show that anions X- slightly affect the reaction rates, however the effect stays almost the same even after their encapsulation in the cavity of bambusurils. We also demonstrate that X- affects the overall reaction rate in the very same way as the reaction rate of the protodeauration step. All results are consistent with the indirect effect of X- by the acidity of the conjugated acid HX on the rate-determining step. There is no evidence that a direct involvement of X- would affect the reaction rate.
ABSTRACT
The glycoluril monomer is a popular building block in supramolecular chemistry as it is used for the synthesis of versatile host molecules which can interact with cationic, anionic or neutral guest molecules. Here we present the design and synthesis of a new hybrid macrocycle containing glycoluril and aromatic units. The reaction afforded a mixture of macrocyclic homologues from which a two-membered macrocycle was isolated as the main product. Two disastereomers of the macrocycle were separated and characterized by means of NMR spectroscopy and X-ray crystallography. Conformational changes of these diastereomers were investigated using DFT models and variable-temperature NMR.
ABSTRACT
The synthesis and supramolecular properties of the first methylene-bridged propanediurea-based dimers are described. These dimers, bearing an aromatic sidewall, have the shape of molecular clips. Unlike glycoluril-based dimers, these clips neither dimerize nor accept any organic guests, due to their small cavities. Both propanediurea- and glycoluril-based dimers bind halide anions on the convex side of the molecules, even in highly polar organic solvents. This observation brings new insights into the mechanism of cucurbituril formation.
ABSTRACT
A novel macrocycle, decamethylpressocucurbit[5]uril (Me10prCB[5]), was synthesized by acid-catalyzed condensation of propanediurea and paraformaldehyde. This macrocycle binds methane with higher affinity than cucurbit[5]uril and its permethylated derivative.
