Conjugated poly alkynes

The Pd-catalyzed C-C coupling (Sonogashira coupling) was applied to polymer synthesis about 20 years ago [23-25], and has especially been developed for the synthesis of n-conjugated poly(aryleneethynylene)s (PAEs) (for reviews, see refs. [16,26-33]). Recently other synthetic routes for PAEs were also developed, e.g., the alkyne metathesis method [28, 34] and the coupling reaction of =C-MR3 with R X (M=Si [35, 36] or Sn [37, 38]). In this review, we are concerned with the synthesis and chemical properties of PAEs with heteroaromatic rings. 

Diynes and triynes refer to alkynes containing two or three triple bonds poly-ynes contain multiple triple bonds. A conjugated triyne is a straight-chain hydrocarbon with triple bonds alternating with single bonds. An examples is... 

In this review, well-defined metal-containing PAEs are described whose primary structure is represented by one of the schematic drawings A-C and E shown in Fig. 2. In contrast to the structures shown in the A-C systems, E has a conjugated phenyleneethynylene with metal chelates as end groups. PAEs containing metal complex as side groups (D) have, up to now, not been described in the literature. The classes of compounds such as metal-bridged alkynes, the poly(metallayne)s, and polymer carbyne complexes (structures G and H) do not in fact represent PAEs. 

Photodimerization of acetylene to give vinylacetylene (butenyne) and formation of polymers in the photolysis of alkynes generally are examples of photoaddition to alkynes. Photopolymerization of di- and poly-ynes has been studied, and for both conjugated diynes or triynes the polymerization process is a 1,4-addition reaction (equation 34). The products are highly unsaturated, and they tend to contain a high proportion of oxygen after exposure to the atmosphere. 

It was also observed that conjugated polymers that are also electrical conductors (see Chap. 10) exhibit optical activity that depends critically on their structural organization [78]. Thus, strong chiroptical properties can be obtained firom substituted polythiophene [79] (Chap. 10) with optically active side chains, especially when the monomers are coupled within the polymer in a regioregular head-to-tail fashion. Actually, optical activity of these materials is only found when the polymers are aggregated at low temperature, in poor solvent, or in solution cast films. This contrasts with other optically active polymers, like polypeptides, poly(l-alkynes) and polyisocyanates that show an optically active conformation of the main chain in the absence of supramolecular association. 

Because silicon is able to conjugate electronically with adjacent alkyne n bonds, poly(silylenealkynylene)s, (SiR2C=C)n (9), can be expected to exhibit conducting or nonlinear optical properties. A very efficient method to synthesize poly(silyleneethynylene) has been reported. Dilithium acetylide prepared from trichloroethylene and butyllithium was treated with Cl2SiR2 to give high molecular weight polymers (Mw = 30,000, when R = CeHs M = 20,000, when R = CeHs, CH3) (eq. 9) (74). 

When used with monomers such as alkynes, metathesis initiators afford poly-conjugated polymers. The reaction mechanism is similar to that of cycloalkene polymerization, with the reaction intermediate being here a metalacyclobutene ... 

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