Polymer Suzuki coupling

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

Pu and co-workers incorporated atropisomeric binaphthols in polymer matrixes constituted of binaphthyl units, the macromolecular chiral ligands obtained being successfully used in numerous enantioselective metal-catalyzed reactions,97-99 such as asymmetric addition of dialkylzinc reagents to aldehydes.99 Recently, they also synthesized a stereoregular polymeric BINAP ligand by a Suzuki coupling of the (R)-BINAP oxide, followed by a reduction with trichlorosilane (Figure 10).100... 

Several microwave-assisted protocols for soluble polymer-supported syntheses have been described. Among the first examples of so-called liquid-phase synthesis were aqueous Suzuki couplings. Schotten and coworkers presented the use of polyethylene glycol (PEG)-bound aryl halides and sulfonates in these palladium-catalyzed cross-couplings [70]. The authors demonstrated that no additional phase-transfer catalyst (PTC) is needed when the PEG-bound electrophiles are coupled with appropriate aryl boronic acids. The polymer-bound substrates were coupled with 1.2 equivalents of the boronic acids in water under short-term microwave irradiation in sealed vessels in a domestic microwave oven (Scheme 7.62). Work-up involved precipitation of the polymer-bound biaryl from a suitable organic solvent with diethyl ether. Water and insoluble impurities need to be removed prior to precipitation in order to achieve high recoveries of the products. 

In a more recent study, Wang and coworkers have discussed microwave-assisted Suzuki couplings employing a reusable polymer-supported palladium complex [141]. The supported catalyst was prepared from commercial Merrifield polystyrene resin under ultrasound Bonification. In a typical procedure for biaryl synthesis, 1 mmol of the requisite aryl bromide together with 1.1 equivalents of the phenyl-boronic acid, 2.5 equivalents of potassium carbonate, and 10 mg of the polystyrene-... 

Scheme 7.119 Suzuki coupling utilizing a polymer-supported palladium catalyst.

Several microwave-assisted procedures have been described for soluble polymer-supported syntheses. Polyethylene glycol) (PEG)-supported aryl bromides have been shown to undergo rapid palladium(0)-catalyzed Suzuki couplings with aryl boronic acids in water (Scheme 12.16) [63], The reaction proceeded without organic cosolvent... 

An inverted system based on the C02-soluble catalyst Pd(OAc)2/PtBu3 has been utilized for Suzuki-coupling of resin-bound substrates [33], The use of scC02 with polymer-supported substrates seems highly attractive owing to the known plasticizing... 

Polymer 163 (and similar alternating copolymers of 9,9-dioctylfluorene and oxadiazole <2002MM3474>) with blue-light-emitting activity were synthesized by the Suzuki coupling reaction and studied by GPC, MALDI-TOF MS, LJV spectroscopy, and several other techniques <2002ANC6252>. 

A divergent protocol for a solid-phase synthesis of 3-substituted 2,5-biarylfurans was reported. Thus, reaction of furan zincate A with polymer bound aryl bromide or iodide provides resin intermediates 61. Subsequent bromination-Suzuki coupling reaction followed by further transformations gives rise to structurally diverse 2,3,5-trisubstituted furans 68 in good overall yields and chemical purities <00TL5447>. 

The Suzuki coupling has been utilized to craft (Toctasubstituted tetramesitylporphyrins using various arylboronic acids [62], and Schluter has adopted this reaction to prepare phenyl-pyrrole mixed polymers 75 [63]. The BOC group is easily removed by heating [64] and polymers with molecular weights of up to 23,000 were synthesized. These polymers are potentiaEy interesting for their electrical and nonlinear optical properties [65]. 

Copolymerization of fluorene with triarylamine compounds was shown to increase the hole-transport properties of the polymers. Several copolymers of triarylamine and fluorene (246-250) synthesized by Suzuki coupling were reported by Bradley et al. [347,348], The hole s... 

Jenekhe and coworkers [430] synthesized a phenothiazine-containing alternating fluorene copolymer 352 by Suzuki coupling (Chart 2.89). The phenothiazine-3,7-diyl fragment in the polymer backbone interrupts the conjugation, and substantially blue shifts absorption... 

A series of terphenylene-vinylene copolymers 491-493 was recently synthesized by Ahn and coworkers [592] via Suzuki coupling. Interestingly, neither alkoxy groups nor pendant phenyl substituents (attached to the vinylene moiety) have any significant effect on the emission properties. The PLEDs fabricated with each of these copolymers (ITO/polymer/Al) emit blue light with AEL —450 nm (above a turn-on voltage of 8-10 V). 

Dow used the Suzuki coupling process to synthesize a variety of fluorene-based homopolymers and copolymers that are able to emit the three primary LED colors red, green, and blue. Structural representations of these polymers are shown in Figure 11.20. The U.S. patents granted to Dow Chemical on OLED emitting materials are listed in Table 11.4. 

Alternatively, boranes can be prepared in solution and then coupled with support-bound carbon electrophiles. The Suzuki coupling of alkylboranes, generated in situ from 9-BBN and alkenes, with brominated cross-linked polystyrene has been used to link substituted alkyl chains directly to the polymer (Entry 4, Table 5.3). Alkylboranes have also been used to alkylate polystyrene-bound aryl iodides (Entries 3 and 5, Table 5.3). 

Palladium catalysts have been found which are effective in the Suzuki coupling reaction of arylboronic acids with aryl chlorides carrying electron-withdrawing groups.73 Biaryls may also be synthesized by cross-coupling of arylboronic acids with arenediazonium salts.74,75 There has been a report of the polymer-bound palladium-catalysed Suzuki coupling of aryl triflates with organoboron compounds.76 Arylbor-onates may themselves be synthesized by the palladium-catalysed reactions of... 

Hyperbranched polymers of polybenzene type can be rendered water-soluble like the above-mentioned monodisperse species by introduction of carboxyl groups [62]. Starting from 3,5-dibromophenylboronic acid 1 as AB2 monomeric building block (Fig. 4.34), the polycondensate 2 was assembled in an aryl-aryl coupling analogous to Suzuki coupling in the presence of Pd(0), and subsequently reacted with carbon dioxide to form the hyperbranched compounds 3 with terminal carboxylate groups ... 

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