Selective Enclathration of Methyl- and Dimethylpiperidines by Fluorenol Hosts

Abstract

Two similar fluorenyl diol hosts H1 and H2 have been employed to study their selectivity toward methylated piperidines. Crystal structures show strong similarities in the packing of these inclusion compounds, but the interesting result arises from the competition of these hosts for equimolar dimethylpiperidines (2,6DMP and 3,5DMP). H1 selects 3,5DMP, while H2 selects 2,6DMP. Packing analysis and lattice energy calculations failed to explain this result, but the differential scanning calorimetry profiles of the four host−guest compounds are in agreement with the selectivity experiments.

Selectivity behaviour of two roof-shaped host compounds in the presence of xylene and ethylbenzene guest mixtures

“…Therefore, these analyses provided the G A :G B ratios in each of the phases, and a plot of Z for G A (or G B ) against X for G A (or G B ) afforded selectivity profiles which depict the selectivity behaviour of the host compound in such varying conditions. 22 The selectivity coefficient, K GA:GB , obtained using the equation K GA:GB = Z GA /Z GB x X GB /X GA , where X GA + X GB = 1, measures the host selectivity. Figures 1a-c and 2a-f were the result of these plots, wherein have been inserted straight lines to demonstrate the behaviour of an unselective host compound (where K = 1) compared with the experimental data points.…”

Enclathration of Picoline Isomers by (rac)-TADDOLs: Structures, Selectivity, and Thermal Analysis

“…3−7 Other isomer mixtures where separation has been carried out in this manner include the isomers of lutidine, 8 phenylenediamine, 9 trimethoxybenzene, 10 and methyl and dimethylpiperidines. 11 The process of inclusion consists of exposing a host to a guest molecule in order to form a host− guest complex or clathrate. The latter are of three kinds: (a) The host molecule itself has a cavity that accommodates the guest.…”

Cyclohexanone-Driven Discriminatory Behavior Change of Host Compound (+)-(2R,3R)-TETROL for Isomeric Methylcyclohexanone Guests

“…It is well-known that host compounds are able to display selectivity in the presence of guests with similar structural features. − As an example, Barbour et al have demonstrated that the octahedral nickel complex, Ni­(NCS) 2 ( para -phenylpyridine) 4 , may be used to separate each of the xylene isomers by means of solid–vapor sorption of these guests, which follows the work of Alaerts et al who used a microporous vanadium­(IV) terephthalate material in a chromatographic separation of these same guests. Nassimbeni and his research team very recently explored the selective enclathration by hosts comprising the fluorenyl moiety for methyl- and dimethyl-piperidine guests, while Mitra and co-workers focused their research efforts on the synthesis of molecular organic cages for the separation of mesitylene from its structural isomer 4-ethyltoluene simply as a result of size and shape differences between these two molecules. The cyclodextrins are another class of highly discriminatory hosts, finding applications in widely varied fields of analytical chemistry, and are efficient at forming reversible inclusion complexes and are therefore able to recognize guests selectively …”