Photocatalytic Isomerization of Stilbenes via Molecular Recognition With a Dual-Function η6-Arene Catalyst.

Abstract

Electron donor-acceptor (EDA) complexes, formed through noncovalent interactions between electron-rich and electron-deficient species, can undergo photoinduced charge transfer to access reactive radical intermediates. However, rapid and unproductive back electron transfer (BET) limits their synthetic utility. Herein, we report a dual-function (η6-arene)rhodium(III) catalyst that enables contra-thermodynamic E-to-Z isomerization of stilbenes via selective EDA complexation. In contrast to well-studied photoisomerization reactions driven by triplet photosensitizers via intermolecular energy transfer (EnT), photoexcitation of the self-assembled EDA complex generates a charge-separated singlet exciplex that undergoes back electron transfer coupled with intersystem crossing to populate a localized triplet-state olefin intermediate. The catalyst plays two pivotal roles: the metal-bound arene scaffold enables molecular recognition of planar (E)-stilbenes over twisted (Z)-isomers through noncovalent interactions, while the heavy rhodium atom promotes ISC.