Triacetylene

Keywords Acetylene chemistry. Cross-coupling reactions, Cyclo[n]carbons, Expanded radialenes. Molecular scaffolding. Nanostructures, Perethynylated chromophores, Poly(triacetylene), Tetraethynylethene. 

This article summarizes efforts undertaken towards the synthesis of the cyclo[ ]carbons, the first molecular carbon allotropes for which a rational preparative access has been worked out. Subsequently, a diversity of perethynylated molecules will be reviewed together, they compose a large molecular construction kit for acetylenic molecular scaffolding in one, two and three dimensions. Finally, progress in the construction and properties of oligomers and polymers with a poly(triacetylene) backbone, the third linearly conjugated, non-aromatic all-carbon backbone, will be reviewed. 

Molecular Wires Oligomers and Polymers with the Poly(triacetylene) (PTA) Backbone... 

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 8. Oligomers and polymers with a poly(triacetylene) (PTA) backbone that are derived from tetraethynylethenes (TEEs)...

In contrast, the synthesis of tetraethynylethene (TEE, C10H4) was described in 1991 and, since then, a rich variety of cyclic and acyclic molecular scaffolds incorporating this carbon-rich molecule as a construction module have been prepared. The majority of these compounds, such as the expanded radialenes or the oligomers and polymers of the poly(triacetylene) type, are highly stable and... 

Die Cadiot-Kupplung von Diacetylen mit dem Acetonid CDXXXV ergibt die Triacetylen-Verbindung CDXXXVI, die durch vorsichtige Hydrolyse in das Triol CDXXXVII iibergefiihrt wird ... 

A rapid and versatile covalent assembly technique starting from DEE oligomers has provided the 11.9 nm long hexadecameric poly(triacetylene) rod 20.1481 With its linearly conjugated 16 double and 32 triple bonds spanning in-between the terminal silicon atoms, compound 20 is currently the longest linear, fully Jt-conjugated molecular wire without aromatic repeat units in the backbone. 

R. E. Martin, T. Mader, F. Diederich, Monodisperse Poly(triacetylene) Rods Synthesis of a 11.9 nm Long Molecular Wire and Direct Determination of the Effective Conjugation Length by UV/Vis and Raman Spectroscopies , Angew. Chem Int. Ed. Engl. 1999,38, 817-821. 

Figure 7.16 (A) Dendron-capped poly(triacetylene) and, (B) soluble oligothiophenes obtained by dendrimers assisted synthesis...

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]...

Incorporation of a third acetylene molecule takes place by CO replacement and without interference with the metallacyclopentadiene ring (170, 371, 379). In the cluster, then, the three acetylene ligands rearrange to a triacetylene ligand of unknown structure before the benzene is liberated (371, 379). 

In the following we will first discuss examples of polytriacetylenes (Fig. 19) and then compare these results with the ones of other molecular structures. Monomers of poly triacetylenes with the three neutral end groups TMS (trimeth-ylsilyl), TES (triethylsilyl), and TIPS (triisopropylsilyl) have been investigated. By deconvolution of the absorption spectra assuming Gaussian fine shapes the wavelengths A00 for the absorption process from the ground state to the zero vibrational mode of the lowest excited state are obtained as described below. 

Martin RE (1998) Monodisperse poly(triacetylene) oligomers, PhD thesis ETH Zurich, No. 12821... 

In another example, the hexaacetylene 109 - after deprotection with potassium carbonate in methanol - is subjected to typical Bergman trapping conditions, resulting in the formation of the anthracene derivative 110 [61]. As a third, more complex illustration, the aroma-tization of the triacetylene 111 may be considered. Here, the 1,4-diradical intermediate faces another triple bond as an internal trap, and, after hydrogen transfer from 1,4-cyclohexadiene, the tricyclic allylic alcohol 112 is produced [61]. 

Linearly n-Conjugated Oligomers and Polymers Poly(triacetylene)s... 

Fig. 13. Progression of linearly re-conjugated all-carbon backbones from trans-polyacetylene (PA) through trans-poly(diacetylene) (PDA), trans-poly(triacetylene) (PTA), to carbyne.

An example which we have studied only cursorily, but which nevertheless reveals much about the importance of molecular distortions in chemical reactions, is the trimerization of acetylene to form benzene (Fig. 9). This reaction was brought to our attention by the work of Vollhardt, who found that a cyclic triacetylene, 1,5,9-cyclo-dodecatriyne, undergoes reaction only at elevated temperature to give products suggestive of the intermediacy of tris-cyclobutenanenzene25. ... 

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. 

For diacetylene and triacetylene the high-intensity bands are beyond the readily accessible range (Table 4), but with dimcthyltriacetylene the bathochromic shift... 

Diacetylene is formed as a significant by-product in the commercial synthesis of acetylene by the pyrolysis of methane and other hydrocarbons . Smaller amounts of triacetylene are also formed . Procedures have been devised for removing and recovering the diacetylenc - . 

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