Transformation of a Pd6 trifacial barrel to a Pd8 tetrafacial barrel by C70 as guest and oxidative photolysis of alkenes using the C70 encapsulated barrel under red light†
Abstract
Fabricating discrete molecular cages as fullerene receptors has been a compelling task. The main objective of confining fullerene molecules is to utilize their physico-chemical properties in commonly used media in which they are insoluble. Herein, a fluorenone-based large trigonal Pd6 molecular barrel (M1) was synthesized by coordination self-assembly to act as a potential fullerene trap. M1, in the presence of fullerene C70, converted to a larger Pd8 tetrafacial barrel (M2) forming stable host–guest adduct, (C70)3@M2. The PF6− analogues of both M1 and (C70)3@M2 were acetonitrile soluble, generated reactive oxygen species due to the presence of photosensitizing fluorenone moieties in their building blocks and catalyzed the oxidative transformation of alkenes into carbonyl compounds under 390 nm irradiation. The presence of encapsulated C70 molecules in (C70)3@M2 enabled its photosensitizing wavelength to be tuned to 650 nm (red light). Subsequently, (C70)3@M2, at low catalyst loadings and under red light irradiation, catalyzed olefin oxidations in acetonitrile wherein free C70 was completely inefficient due to insolubility. In summary, (C70)3@M2 was employed as a photocatalyst to mimic the ozonolysis of olefins without the use of ozone or other metal-oxide oxidants that produce over-oxidized products and generate toxic waste, under innocuous red light irradiation and environment-friendly reaction conditions.