Carboxylic acid and metal ion co-driven assembly of triene coordination polymers for [2 + 2] photocycloaddition

Abstract

The application of coordination polymers (CPs) as a platform to control the arrangement of olefin-containing ligands to produce cyclobutane derivatives by [2 + 2] photocycloaddition reactions is a highly regioselective and stereoselective approach. However, current research is mainly focused on mono-olefin and di-olefin ligand-based CPs, and research on the photocycloaddition of multi-olefin ligand-based CPs, which will greatly enrich the chemistry of cyclobutane isomers, is still lacking. Herein, we present a strategy to fine-tune the orientation and distance of a triene ligand, 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene (tpeb), which is accomplished by carboxylic acid and metal ion co-driven assembly of six kinds of CPs. Five kinds of arrangements of tpeb ligands were realized and the [2 + 2] photocycloadditions of these CPs under UV light irradiation were precisely controlled to produce di- and tri-cyclobutanes, which were monitored by proton nuclear magnetic resonance (¹H NMR) and X-ray diffraction (XRD). This work not only widens the synthetic scope of multi-cyclobutanes and their derivatives but also provides a reference for the precise control of the functional groups of organic molecules in the frameworks of CPs.