Expected and unexpected photoreactions of 9-(10-)substituted anthracene derivatives in cucurbit[<i>n</i>]uril hosts

Abstract

By arranging substrates in a "reaction ready" state through noncovalent interactions, supramolecular nanoreactors/catalysts show high selectivity and/or rate acceleration features. Herein, we report the host-guest complexation of 9-(10-)substituted anthracene derivatives (<b>G1-G3</b>) with cucurbit[<i>n</i>]uril (CB[<i>n</i>], <i>n</i> = 8, 10), and the photoreactions of these derivatives in the presence of CB[<i>n</i>] hosts. Both CB[10] and CB[8] showed no obvious effects on the photoreaction of 9,10-disubstituted derivative <b>G1</b>. For <b>G2</b> and <b>G3</b>, CB[10] operated as either a nanoreactor or catalyst (10%) for the photodimerization of two compounds with high selectivity and high yield. However, although CB[8] formed a 1 : 2 complex with <b>G2</b>, as also observed with CB[10], the photosolvolysis product (9-anthracenemethanol) was obtained quantitatively after photoirradiation of the CB[8]·2<b>G2</b> complex. This unexpected photosolvolysis was rationalized by a plausible catalytic cycle in which anthracene acts as a photoremovable protecting group (PPG) and the carbonium ion intermediate is stabilized by CB[8].