Role of π-π Stacking and Halogen Bonding by 1,4-Diiodoperchlorobenzene to Organize the Solid State to Achieve a [2 + 2] Cycloaddition Reaction
The formation of a series of polymeric isostructural solids that utilize 1,4-diiodoperchlorobenzene (C6I2Cl4) as a halogen bond donor has been achieved. These cocrystals are based upon C6I2Cl4 along with one of three isosteric bipyridines, namely, trans-1,2-bis(4-pyridyl)ethylene (BPE), 4,4′-azopyridine (AP), or 1,2-bis(4-pyridyl)acetylene (BPA). In all cases, a one-dimensional chain is formed that is held together by I···N halogen bonds in which molecules of C6I2Cl4 stack in a homogeneous face-to-face -πstacking orientation. As a consequence of this type of interaction, the various halogen bond acceptors also engage in a similar homogeneous stacking arrangement. Because of this stacking pattern, the carbon-carbon double bonds (C?C) within (C6I2Cl4)·(BPE) are found to be parallel and within the correct distance to undergo a solid-state [2 + 2] cycloaddition reaction. Upon exposure to ultraviolet light, (C6I2Cl4)·(BPE) undergoes a stereoselective and high yielding photoreaction (ca. 89%) that produces rctt-tetrakis(4-pyridyl)cyclobutane (TPCB). A photoreactive material was also achieved via a solvent-free approach where dry vortex grinding of both C6I2Cl4 and BPE resulted in a solid that also undergoes a [2 + 2] cycloaddition reaction with a similar overall yield. Density functional theory calculations demonstrate that the homogeneous ?-πstacking that is observed in each cocrystal is preferred when compared to the hypothetical heterogeneous stacking pattern of the aromatic rings.
Bosch, Eric, Samantha J. Kruse, Herman R. Krueger Jr, and Ryan H. Groeneman. "Role of π–π Stacking and Halogen Bonding by 1, 4-Diiodoperchlorobenzene To Organize the Solid State To Achieve a [2+ 2] Cycloaddition Reaction." Crystal Growth & Design 19, no. 6 (2019): 3092-3096.
Crystal Growth and Design