Chemical reactions in single crystals often occur with perfect product selectivity. We employed this to prepare the first alternating polydiacetylene copolymers, and we observed an unusual dimerization of bromodiacetylenes that was the first complex, multistep reaction in a single crystal. Key Publications. Nature Chem. 2013, J. Am. Chem. Soc. 2008, J. Am. Chem. Soc. 2006, Chem. Eur. J. 2008.
State of the Research
Organic molecules often display unusual physical or chemical properties in a confined environment such as the crystalline state, because of the precise arrangement of functional or reactive groups, the constrained degrees of conformational freedom, defined and close supramolecular interactions, and the absence of competing molecules (Desiraju, Angew. Chem. Int. Ed. 2007, 46, 8342). Chemical reactions in single crystals require a specific arrangement of the reactants but then typically proceed under mild conditions and with perfect product selectivity. Prominent examples are the topochemical diacetylene polymerizations or photocyclodimerizations of alkenes. With the exception of unimolecular rearrangements, however, all previously reported examples are single-step transformations, following the topochemical postulate of minimal atomic displacements. Complex chemical reactions in single crystals had not been described.
Expanding on our work on the polymerization of reactive diacetylenes in self-assembled nanofibrils, we performed chemical reactions in single crystals obtained by crystal engineering, that is, the use of specific supramolecular interactions to control the intermolecular arrangement. We reported an unusual dimerization of bromodiacetylenes that involved the cleavage and formation of several bonds and constituted the first example of a complex, multistep organic reaction in a single crystal (Nature Chem. 2013). Moreover, we employed quadrupolar interactions between aryl and perfluoroaryl groups to preorganize diacetylene monomers in single crystals and accomplished the first alternating polydiacetylene copolymer, resulting in one of the few examples of soluble and well-characterized polydiacetylenes, and one of the first examples of a polytriacetylene (J. Am. Chem. Soc. 2008, Chem. Eur. J. 2008, J. Am. Chem. Soc. 2006).