Crystal structure and photoreactivity of a halogen‐bonded cocrystal based upon 1, 2‐diiodoperchlorobenzene and 1, 2‐bis(pyridin‐4‐yl)ethylene. Issue 6 (13th May 2020) - Bosch, Eric
Abstract : The role of I…N halogen bonding as a driving force to organize the organic solid state to achieve a [2 + 2] cycloaddition reaction is presented. Within the cocrystal, the halogen‐bond donor 1, 2‐diiodoperchlorobenzene is found to π–π stack in a homogeneous and face‐to‐face pattern, thereby positioning the reactant molecule, trans ‐1, 2‐bis(pyridin‐4‐yl)ethylene, in the correct orientation to undergo a solid‐state photoreaction. Abstract : The formation of a photoreactive cocrystal based upon 1, 2‐diiodoperchlorobenzene (1, 2‐C6 I2 Cl4 ) and trans ‐1, 2‐bis(pyridin‐4‐yl)ethylene (BPE ) has been achieved. The resulting cocrystal, 2(1, 2‐C6 I2 Cl4 )·(BPE ) or C6 Cl4 I2 ·0.5C12 H10 N2, comprises planar sheets of the components held together by the combination of I…N halogen bonds and halogen–halogen contacts. Notably, the 1, 2‐C6 I2 Cl4 molecules π‐stack in a homogeneous and face‐to‐face orientation that results in an infinite column of the halogen‐bond donor. As a consequence of this stacking arrangement and I…N halogen bonds, molecules of BPE also stack in this type of pattern. In particular, neighbouring ethylene groups in BPE are found to be parallel and within the accepted distance for a photoreaction. Upon exposure to ultraviolet light, the cocrystal undergoes a solid‐state [2 + 2] cycloaddition reaction that produces rctt ‐tetrakis(pyridin‐4‐yl)cyclobutane (TPCB ) with an overall yield of 89%. A solvent‐free approach utilizing dry vortex grinding of the components also resulted in a photoreactive material with a similar yield.