Supramolecular Catalysis in the Organic Solid State through Dry Grinding.

We report a ditopic supramol. receptor, in the form of the bifunctional hydrogen-bond donor 4,6-dichlororesorcinol (4,6-diCl-res) that operates as a supramol. catalyst in the absence of solvent (Figure 1). The catalytic reaction is a [2+2] photodimerization of trans-1,2-bis(4-pyridyl)ethylene (4,4'-bpe). The reaction results in the stereospecific formation of rctt-tetrakis(4-pyridyl)cyclobutane (4,4'-tpcb) in near quant. yield. We employ mechanochem. energy in the form of dry mortar- and-pestle grinding, in a two-step process that we demonstrate results in reactions between different cryst. phases. [on SciFinder(R)]