Triacetylene topochemical polymerization

Supramolecular synthesis is the process, using noncovalent bonds, to organize molecules with certain defined supramolecular structural features. Because of the difficulty of determining the supramolecular structure of noncrystalline materials supramolecular synthesis is often applied to prepare crystalline materials. X-ray crystaUf raphy is without peer for the ability 

In initial studies the 2,5-diaminoquinone system 19 was prepared [33]. The X-ray crystal structure of this compound demonstrated that the 2,5-diaminoquinone assembled with a molecular repeat distance of 7.46 A, which is close to the dm value of 7.4A believed to be suitable for a topochemical polymerization (Fig. 5.8). Unfortunately, these simple 2,5-diaminoquinones proved to be very insoluble and not suitable for host-guest studies. However, the sub-structural feature responsible for the repeat distance is the vinylogous amide. Simple vinylogous amides such as 20 should have better solubility properties although the persistency of this functional group to assemble into the required motif is more problematical [35] . Among the 

Diederich and co-workers have successfully prepared the conjugated poly(triacetylene) backbone, not by triacetylene polymerization but by the coupling of enediynes. Their considerable studies on these conjugated polymers have revealed some intriguing properties with possible application to advanced materials. For a review see Ref 32. If the molecular repeat distance (dm) is 7.4 A and the closest van der Waals approach of atoms C1-C6 of adjacent triacetylenes is 3.5 A then the angle yi) of the triacetylene chains 

AU of the six vinylogous amides with structure 20 reported in the CSD have the supramolecular chemistry shown in Fig. 5.8. However only one (ZAMVEO) assembles using the necessary simple translational motif The remaining five examples assemble using a glide plane or screw axis. These types of symmetry double the crystallographic repeat distance to an undesirable 14-15 A [34]. 

Fortunately, the above strategy for the preparation of supramolecular structures has flexibility. Another approach to the desired supramolecular structure is to attach the hydrogen bond donor (carboxylic add) to the guest triacetylene and the 

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Scheme S.7. Proposed supramolecular structure features required for a topochemical triacetylene polymerization.

The polydiacetylenes and polytriacetylenes differ from polyacetylene because preorganization of the diacetylene and triacetylene is required for a successful polymerization (7). This remarkable observation was first recognized (8,9) in 1969 and marks the beginning of modern polydiacetylene and polytriacetylene chemistry. In a few cases, this topochemically controlled polymerization occurs from a crystal of the monomer to a crystal of the polymer, giving rare examples of macroscopic single polymer crystals (9). 

Preparation of Polytriacetylene. Soon after the early understanding of the diacetylene polymerization was reported (8,9), attempts were made to polymerize a triacetylene to produce a polytriacetylene (45). However, these early attempts as well as more recent efforts (7) were not successful. The difficulty of the topochemically controlled polymerization is the organization of the triacetylene monomer with a translational repeat distance of about 0.74 nm. 

Polytriacetylenes have recently been prepared by a topochemically controlled polymerization of a triacetylene. This was accomplished using the host-guest strategy (Fig. 8). A vinylogous amide was used to establish the required translational repeat distance and y-rays were necessary to induce the polymerization (48). 

The preparation of new polydiacetylenes and polytriacetylenes is complicated by the fact that no one has demonstrated a direct 1,4-diacetylene or a 1,6-triacetylene polymerization in solution, 1,2-polymerizations being more favorable. However, the polymers can be prepared in the solid state as the result of a topochemical polymerization. Topochemical reactions are solid state reactions in which the product and the regio- and stereochemistry of a reaction are directly controlled by the preorganization of the reactants. 

Unsuccessful attempts to perform a topochemical single crystal to single crystal polymerization of triacetylene have been reported over the years [29). The difficulty of this reaction is that previous studies and molecular modeling [30, 31] of the polymer suggest a molecular repeat of about 7.4 A will be required for a successful 1,6-polymerization of a triacetylene 17 (Scheme 5.7). A dose approach, of the... 

Figure S.8. Possible hosts to organize triacetylenes with 7.4 A spacing along the stacking direction for a topochemical polymerization.

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