Triacetylene polymerization

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. 

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

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... 

Oxidative polymerization of trans-bis-deprotected 79 under Hay coupling conditions [54] yielded, after end-capping with phenylacetylene, the high-melting and readily soluble oligomers 80a-e with the poly (triacetylene) backbone [87,106] (Scheme 8). Poly(triacetylene)s [PTAs,-(C=C-CR=CR-C=C) -] are the third class of linearly conjugated polymers with a non-aromatic allcarbon backbone in the progression which starts with polyacetylene [PA,... 

Scheme 9 Strategy for the 1,6-polymerization of triacetylene, a Polymerization principles for triacetylene, b Supramolecular synthon as the host to arrange triacetylene molecules as the guest with a stacking distance of 7.4 A. c Successful and unsuccessful examples for the combination of host and guest molecules with carboxylic acid or pyridine moieties [63]...

Polymeric species Pt(X"Bn3)2 =C (C=C)m-C C and Pt(X Bn3)2-(C=C) 6H4-(C=C) -ju (m = 0, 1) have been synthesized. The absorption and emission spectra of these complexes showed extended tt-electron conjngation throngh the metal sites on the chain, with a lower itt-itt energy gap for the triacetylenic than for the diacetylenic polymers. Well-resolved vibronic stracture associated with the v(C=C) frequency was observed in both the absorption and emission spectra, indicating strong electron-phonon coupling for these polymers. 

Xiao. J. Yang. M. Lauher. J.W. Fowler. F.W. A supramolecular solution to a long-standing problem The 1,6-polymerization of a triacetylene. Angew. Chem., Int. Ed. Engl. 2000. 39, 2132-2135. 

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). 

More recently, ring opening metathesis polymerization (ROMP) has been used to prepare telechelic liquid crystalline polymers that carry azide end groups which can be crosslinked with a triacetylene species using the well known copper catalyzed click chemistry [22]. 

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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