Crystal Engineering for Topochemical Polymerization of Muconic Esters Using Halogen−Halogen and CH/π Interactions as Weak Intermolecular Interactions

• Published in: Journal of the American Chemical Society 2002-07, Vol.124 (30), p.8891-8902
• Main Authors: Matsumoto, Akikazu, Tanaka, Toshihiro, Tsubouchi, Takashi, Tashiro, Kohji, Saragai, Seishi, Nakamoto, Shinsuke
• Format: Article
• Language: English
• Subjects: Aliphatic, non-condensed and condensed benzenic, and alicyclic compounds; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Organic compounds; Organic polymers; Physicochemistry of polymers; Physics; Polymers with particular structures; Preparation, kinetics, thermodynamics, mechanism and catalysts; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0205333

We now report the molecular and crystal structure design of muconic ester derivatives on the basis of crystal engineering using halogen−halogen contacts and CH/π interactions. The solid-state photoreaction pathway of the dibenzyl (Z,Z)-muconates as the 1,3-diene dicarboxylic acid monomers depends on the structure of the ester groups. The substitution of a halogen atom for the aromatic hydrogen of a benzyl group induces topochemical polymerization to produce stereoregular polymers in a crystalline form, whereas the unsubstituted benzyl derivative isomerizes to yield the corresponding E,E isomer under similar conditions. The topochemical polymerization process is directly confirmed by the fact that the single-crystal structures before and after the polymerization are very similar to each other. From the crystal structure analysis for a series of substituted benzyl (Z,Z)- and (E,E)-muconates, it has been revealed that the planar diene moieties are closely packed to form a columnar structure in the crystals. The stacking of the polymerizable monomers is characterized by a stacking distance of 4.9−5.2 Å along the columns. This structure is supported by a halogen−halogen interaction between the chlorine or bromine atoms introduced at the p position of the benzyl groups in addition to an aromatic stacking due to the CH/π interaction between the benzylic methylene hydrogens and aromatic rings. The design of a monomer packing corresponds to the type and position of the introduced halogen atom and also the polymorphs. To make a stacking distance of 5 Å using both halogen−halogen and CH/π interactions as supramolecular synthons is important for the molecular design of muconic ester derivatives appropriate for topochemical polymerization.