Construction of Photoreactive Chiral Metal-Organic Frameworks and Their [2+2] Photocycloaddition Reactions

Abstract

Here, we report a uniqueenantiopure pair of metal-organicframeworks (MOFs) capable of [2 + 2] cycloaddition reaction by theself-assembly of a bipyridyl olefin ligand and either d-camor l-cam (both enantiopure forms of camphoric acid). Chiral metal-organic frameworks (CMOFs) and solid-state[2 + 2] photocyclization have been explored as independent areas incrystal engineering. We herein report the photoreactive CMOFs thatundergo a [2 + 2] photocycloaddition reaction for the first time.Through the incorporation of a dipyridyl olefin ligand, 1,4-bis[2-(4-pyridyl)ethenyl]benzene,and d-camphoric acid or l-camphoric acid, we constructeda pair of homochiral Zn(II) CMOFs (d-1 or l-1) with a two-dimensional sql topology via atwo-step procedure to avoid racemization. Both d-1 and l-1 were photoinert due to the large olefinbond separation. The removal of the solvent molecules between layersenabled them (d-1a and l-1a) to undergo [2 + 2] cycloaddition reactions; d-1a is more reactive (70%) than l-1a (20%) probablydue to proper desolvation-induced rearrangement. The photoluminescenceproperties are also discussed. This work presents a new perspectiveon photoreactive homochiral network materials with diverse topologiesand applications.