Expanding the application of chlorinated anilines as molecular templates to achieve a series of solid-state [2 + 2] cycloaddition reactions

The ability to achieve a series of solid-state [2 + 2] cycloaddition reactions within related hydrogen-bonded co-crystals is reported. These multicomponent molecular solids contain either <i>trans</i>-1,2-bis(3-pyridyl)ethylene (<b>3,3-BPE</b>) or <i>trans</i>-1,2-bis(2-pyridyl)ethylene (<b>2,2-BPE</b>) as the reactant, along with one of two chlorinated anilines that behave as a template, namely 2,3,5,6-tetrachloroaniline (<b>C</b> _<b>6</b> <b>H</b> _<b>3</b> <b>Cl</b> _<b>4</b> <b>N</b>) or 2,4,6-trichloroaniline (<b>C</b> _<b>6</b> <b>H</b> _<b>4</b> <b>Cl</b> _<b>3</b> <b>N</b>). For each of the four unique organic solids, the co-crystallization process yields a three-component hydrogen-bonded assembly with a formula of either 2(<b>C</b> _<b>6</b> <b>H</b> _<b>3</b> <b>Cl</b> _<b>4</b> <b>N</b>)·(<b>3,3-BPE</b>), 2(<b>C</b> _<b>6</b> <b>H</b> _<b>4</b> <b>Cl</b> _<b>3</b> <b>N</b>)·(<b>3,3-BPE</b>), 2(<b>C</b> _<b>6</b> <b>H</b> _<b>3</b> <b>Cl</b> _<b>4</b> <b>N</b>)·(<b>2,2-BPE</b>), or 2(<b>C</b> _<b>6</b> <b>H</b> _<b>4</b> <b>Cl</b> _<b>3</b> <b>N</b>)·(<b>2,2-BPE</b>). In all co-crystals, these anilines template up to a quantitative yield for the photoreaction since they are able to engage in both N-H···N hydrogen bonds and homogeneous face-to-face π-π stacking interactions, which position the ethylene groups within the different reactant molecules in a suitable location to photoreact. These results complete the series for the remaining symmetric bipyridine-based reactants to undergo a solid-state [2 + 2] cycloaddition reaction utilizing these chlorinated anilines. This work expands and illustrates the potential for these chlorinated anilines to serve as reliable molecular templates that crystal engineers can utilize to control the organic solid state and achieve photoreactions.