Sonogashira coupling reaction polymers

Aqueous palladium-catalyzed Sonogashira coupling reactions were also applied for the preparation of polymers (see Chapter 7). 

Xia, M., Wang, Y.-G. A novel microwave-activated Sonogashira coupling reaction and cleavage using polyethylene glycol as phase-transfer catalyst and polymer support. J. Chem. Res., Synop. 2002,173-175. 

The polycondensation of acetylene-substituted metallocenes has yielded polymers containing backbone aUcyne bridges. The synthesis of l-iodo-2-methoxy-methyl-3-ethynylferreocene and l-iodo-2-(N,N-dimethylamino methyl)-3-ethynyl-ferreocene was reported by Plenio and coworkers. Polymerization of these ferrocene-based complexes gave rise to soluble bimodal 1,3-linked ferrocene-acetylene polymers. Polymers exhibiting optical activity or functionalized sidechains were produced via Sonogashira coupling reactions. 

Concerning other metals, Sonogashira coupling products have also been observed in the reaction of Ag(l)-carbenes [133] and Au(I)-supported carbenes [134] in low to moderate yields, but only under harsh conditions (more than 100°C). In this regard, NHC based catalysts for Sonogashira reactions have been supported on different materials that include clays [135], polymers [136] and peptides [137]. 

Another palladium-catalyzed coupling reaction that has been successfully performed on soluble polymers is the Sonogashira coupling. Xia and Wang have presented an approach in which the PEG 4000 utilized simultaneously serves as polymeric support, solvent, and phase-transfer catalyst (PTC) in both the coupling and... 

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. 

Solid-phase synthesized polymer-bound 3-iodoindole 845 subjected to the Sonogashira and Suzuki coupling reactions afforded the corresponding coupling products 846 and 847 in 91% and 80% yields, respectively, as determined by transesterification and isolation of the corresponding methyl esters (Scheme 161) <2005JC0809>. 

Discoveries made in the late 1970s of electrical conductivity in conjugated polymers spawned a monumental interest in the study of these materials, which are ideally suited for synthesis via cross-coupling reactions. Yamamoto was the first to realize this possibility with a regiochemicahy defined synthesis of poly(/ -phenylene) formed via the Kumada-Corriu protocol. Since then, various cross-coupling reactions have been applied in condensation polymerization reactions,with the Suzuki and Sonogashira protocols gaining the most widespread use. 

Another palladium-catalyzed coupling reaction performed successfully on soluble polymers is the Sonogashira coupling. In a more recent report it was reported that PEG 4000 acts simultaneously as polymeric support, solvent, and phase transfer catalyst (PTC) in both steps, coupling and hydrolysis [72]. Poly(ethylene glycol) (PEG)-bound 4-iodobenzoic acid was readily reacted with several terminal alkynes under rapid microwave conditions (Scheme 16.50). Cleavage of the coupling products from the PEG support was achieved efficiently by simple saponification with brief microwave irradiation in an open beaker in a domestic microwave oven. 

PNIPAM-bound phosphines have been used to prepare catalysts like the Pd(II), Pd(0), Rh(I) transition metal catalysts 76, 77, and 81-83 [115-117]. Thesecatalysts can be used in carbon-carbon bond forming reactions like Heckreactions, Suzuki couplings, or Sonogashira couplings. After use as a cat-alystin reactions like Eqs. 31 or 32, the polymer-bound Pd or Rh catalyst can be recovered by heating if the reaction is carried out in water or by solvent precipitation in other solvents. 

---