Tuning light-driven oxidation of styrene inside water-soluble nanocages

Abstract

AbstractSelective functionalization of innate sp2 C-H bonds under ambient conditions is a grand synthetic challenge in organic chemistry. Here we combine host-guest charge transfer-based photoredox chemistry with supramolecular nano-confinement to achieve selective carbonylation of styrene by tuning the dioxygen concentration. We observe exclusive photocatalytic formation of benzaldehyde under excess O2 (>1 atm) while Markovnikov addition of water produced acetophenone in deoxygenated condition upon photoexcitation of confined styrene molecules inside a water-soluble cationic nanocage. Further by careful tuning of the nanocage size, electronics, and guest preorganization, we demonstrate rate enhancement of benzaldehyde formation and a complete switchover to the anti-Markovnikov product, 2-phenylethan-1-ol, in the absence of O2. Raman spectroscopy, 2D 1H-1H NMR correlation experiments, and transient absorption spectroscopy establish that the site-selective control on the confined photoredox chemistry originates from an optimal preorganization of styrene molecules inside the cavity. We envision that the demonstrated host-guest charge transfer photoredox paradigm in combination with green atom-transfer reagents will enable a broad range of sp2 carbon-site functionalization.