Influence of Fluorine Substitution on the Unusual Solid-State [2 + 2] Photo-Cycloaddition Reaction between an Olefin and an Aromatic Ring

Abstract

Solid-state [2 + 2] photo-cycloaddition reactions observed so far were exclusively between a pair of olefin bonds. Usually when the phenyl–olefin bonds have been closely aligned, they were found to be either photoinert or sliding of molecules takes place for [2 + 2] cycloaddition reaction between olefins in the solid state, although intramolecular phenyl–olefin reactions are well-known in solution. In the crystal structure of [Zn2(ptol)4(4spy)2] (ptol = para-toluate), the neighboring 4-styrylpyridine (4spy) ligands are organized in a head-to-tail manner. On one side of the complex in the crystal structure, the olefin bonds in the 4spy pairs are perfectly aligned to undergo cycloaddition reaction, but on the other side, the olefin bond pairs are slightly offset and found to be photoinert at 223 K forming only a dimer in single crystals. The sliding of 4spy groups has been restricted by the steric hindrance of the adjacent methyl group of the ptol ligands. A similar packing of 2-fluoro-4′-styrylpyridine (2F...