Palladium-catalyzed coupling, poly

Y. Li, G. Vamvounis, J. Yu, and S. Holdcroft, A novel and versatile methodology for functionalization of conjugated polymers. Transformation of poly(3-bromo-4-hexylthiophene) via palladium-catalyzed coupling chemistry, Macromolecules, 34 3130-3132, 2001. 

Keywords Poly(aryleneethynylene) Heteroaromatic ring Palladium-catalyzed coupling Optical properties Chemical reactivity... 

The initial catalyst systems described above were effective with aryl bromides and a relatively narrow array of amines, although these procedures found utility in the preparation of diaminofluorenes [22], poly(aryleneamines) [23], certain iV-aryl-aza-crown ethers [24], N -arylpiperazines [25], and diaminobenzenes [26] (Fig. 1). These original methods often proved reasonably effective in the coupling of cyclic amines. Presumably, cyclic amines are less challenging substrates for the palladium-catalyzed coupling because the cyclic palladium (II) amide intermediates are less prone to /1-H elimination compared to their acyclic counterparts. 

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. 

Izumi and coworkers carried out similar preparations of conjugated polymers with azobenzenes in the main chain [212, 213]. Application of various palladium-catalyzed coupling methods such as the Suzuki coupling and the Heck reactions allowed formation of poly(p-phenylene)- and poly(phenyl vinylene)-based polymers ... 

M. Rehahn, A. D. Schlueter, G. Wegner, W. J. Feast, Soluble poly(para-phenylenes). 2. Improved synthesis of poly(para-2,5-di-n-hexylphenylene) via palladium-catalyzed coupling of 4-bromo-2,5-di-n-hexylbenzeneboronic acid, Polymer 1989, 30, 1060. 

Conjugated polymetallocenes are an important class of organometallic poly-mers. Scheme 36 shows the synthesis of polyaryleneethynylenes with ferrocene units in their backbones (138) via a palladium-catalyzed coupling reaction of... 

The Suzuki reaction was also used to prepare the polyketone since this particular reaction tolerates the subsequent step (Scheme 6.19).135 Palladium-catalyzed cross-coupling of aromatic diacid chlorides and bis(trimethylstannane) monomers was utilized to prepare poly(arylene ether ketone)s.136... 

Bunz demonstrated a facile procedure for the preparation of high quality PAEs by a palladium-catalyzed cross-coupling reaction of acetylene gas with diiodoarenes. The polymerization proceeds at 50 °C, and poly(phenylene-ethynylene)s 114 were produced. Catalyst loadings of 0.1-0.2 mol% of palladium were best to achieve the complete i ... 

Kuroboshi, M. Waki, Y. Tanaka, H. Palladium-catalyzed tetrakis(dimethylamino)ethy-lene-promoted reductive coupling of aryl halides./. Org. Chem. 2003, 68, 3938-3942. Luo, F.-T. Jeevanandam, A. Basu, M. K. Efficient and high-turnover homocoupling reaction of aryl iodides by the use of palladacycle catalysts. A convenient way to prepare poly-p-phenylene. Tetrahedron Lett. 1998, 39, 7939-7942. 

Wang L, Zhang Y, Liu L et al (2006) Palladium-catalyzed homocoupling and cross-coupling reactions of aryl halides in poly(ethylene glycol). J Org Chem 71(3) 1284-1287... 

Lipshutz and colleagues presented recently palladium-catalyzed direct coupling reactions of alkyl iodides and vinyl bromides or iodides catalyzed by 1 mol% Pd(amphos)Cl2 in the presence of zinc and TMEDA in a biphasic aqueous/poly-(ethylene glycol tocopheryl sebacate) reaction medium [198], Internal olefins were obtained in 51-95% yield. For aryl-substituted (Aj-vinyl bromides, retention of double bond geometry was observed, while different degrees of isomerization occurred for (Z)-isomers, which may indicate the intervention of a radical addition process in the course of the coupling process. Alkyl-substituted (Z)-vinyl halides were transformed in contrast with retention of alkene geometry. Aryl halides also reacted [199],... 

The two linear poly(phenyleneethynylene) structures 88 and 89 <1995JA7017, 1995JA12593>, synthesized by a palladium-catalyzed cross-coupling reaction, act as very sensitive fluorescence chemosensors by forming in the presence of paraquat side-chain polypseudorotaxanes. Binding of the analyte causes a quenching of the fluorescence associated with the polymer backbone much more pronounced than that observed for a model monomeric species. 

---