Minor modifications afford improved host selectivities in xanthenyl-type host systems

Abstract

In this work, we examine the selectivity of host N,N′-bis(9-phenyl-9-xanthenyl)ethylenediamine in the presence of two different guest series', namely the C8 aromatic fraction of crude oil (i.e., ethylbenzene, and o-, m- and p-xylene) and anisoles (anisole, and o-, m- and p-methylanisole). Of the four alkyl aromatics, only p-xylene formed a complex with this host when it was recrystallized from each one, while both anisole and p-methylanisole from the second guest series were clathrated in this way. Host : guest ratios were consistently 1 : 1. When this host was recrystallized from various mixtures of the solvents from the two guest groups, an unequivocal bias towards p-xylene and p-methylanisole, respectively, was observed, with the other competing guests essentially being excluded from the host crystal in these experiments. Furthermore, this host displayed significantly enhanced selectivities relative to the structurally-related compound, N,N′-bis(9-phenyl-9-thioxanthenyl)ethylenediamine, in the presence of the xylenes and ethylbenzene, when considering a previous report. The latter compound was also assessed for inclusion behaviour in the presence of the anisoles and, once more, its inferior selectivity compared with the oxo-host counterpart was strikingly evident. Both single crystal X-ray diffraction and thermal experiments were conducted in order to investigate the noted selectivity differences.