Suzuki polycondensation

Over the past two decades, Suzuki polycondensation has become one of the most efficient methods for the synthesis of conjugated polymers. As another important cross-coupling protocol, the Suzuki-Miyaura cross-coupling reaction was invented by Suzuki and co-workers in 1979. The scope of the Suzuki reaction for synthetic applications has been surveyed in several excellent reviews by Kotha, Lahiri, Kashinath, Miyaura and Fu. The Suzuki-Miyaura cross-coupling reaction provided deeper insights into how to connect two specific sp -hybridized C-atoms more efficiently and under milder conditions. The Suzuki-Miyaura cross-coupling reaction was first used by Schlueter et al. to prepare poly(para-phenylene)s.  

Since then, Suzuki polycondensation (SPC) has become one of the most powerful and widely used methodologies for the synthesis of eonjugated polymers. 

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Y. Wu, J. Li, Y. Fu, and Z. Bo, Synthesis and extremely stable blue light emitting poly(spirobi-fluorene)s with Suzuki polycondensation, Org. Lett., 6 3485-3487, 2004. 

Frahn, J., Karakaya, B., Schafer, A. and Schltiter, A.-D. (1997) Suzuki polycondensation On catalyst derived phosphorus incorporation and reproducibility of molecular weights. Tetrahedron, 53,15459-67. 

Research on dendrimers was first focused on synthetic aspects concerning this new class of macromolecules, and a broad range of dendrimers is now available, some even commercially. The emphasis of current study has shifted from merely synthetic aspects to questions of practical applications of dendrimers and the ways in which these unique compounds are superior to known systems. Consequently, much more useful synthetic procedures are required. Schliiter et al. have reported the synthesis of dendrimers with poly(p-phenylene) (PPP) derived cores using the Suzuki polycondensation [139]. 

These approaches have been adopted more recently to incorporate phosphorescent chromophores into PF in order to make use of the fact that a large proportion (up to 75%) of all excitons formed in LEDs are triplet states, whose energy can only be harvested by using phosphorescent units. The first fluorene copolymers with phosphorescent units 34-35 were made by Holmes and coworkers who added monobrominated red- or green-emitting iridium complexes to an AA-BB Suzuki polycondensation [57]. With short fluorene chains, only emission from the iridium complexes are observed, but with longer fluorene chains some blue emission is also seen. Other groups have since incorporated different phosphorescent units such as platinum [58] or zinc salen [59] units or porphyrins [60,61 ]. 

Scherf and Mullen prepared (Scheme 47) the ladder-type polyphenylene (LPPP, 5) with methine bridges [126-129], via a poly(diacylphenylene-co-phenylene) precursor copolymer 103 obtained by an AA-BB type Suzuki polycondensation. The key step is the polymer analogous Friedel-Crafts ringclosing reaction on the polyalcohol 104, obtained by the reduction of 103. This was found to proceed quickly and smoothly upon addition of boron-trifluoride to a solution of 104 in dichloromethane. The reaction appeared to be complete by both NMR and MALDI-TOF analysis, indicating the presence of less than 1% of defects due to incomplete ring closure. LPPPs with num-... 

Another way to introduce Ir(III) complexes into the main-chain of polyfluorenes was realized by Suzuki polycondensation of fluorene segments and /3-diketone ligand chelated with Ir(III) chloride-bridged dimmer (polymer 26 and 27) [34,35]. A saturated red-emitting polymer light-emitting diode was achieved from the device ITO/PEDOT/polymer 27 + PBD (40%)/Ba/Al with the maximum external quantum efficiency of 0.6% at the current density (J) of 38.5 mA/cm2 and the maximum luminance of 541 cd/m2 at 15.8 V. 

Polyfluorene with on-chain ruthenium complex (polymer 49) has been synthesized by Suzuki polycondensation [77]. The photoluminescence of the copolymer was slightly blue-shifted as the concentration of dipyridy-lamine increased. The introduction of dipyridylamine and the ruthenium complex into the polymer significantly improved the photoluminescence efficiency. 

Hereby, poly(p-phenylene) polymers containing ether and carbonyl linkages in the polymer backbone are accessible. By polymerization of the AB2 monomer 3,5-dibromobenzene boronic acid in a biphasic aqueous/organic medium, Kim and Webster obtained hyperbranched polyphenylenes [233]. Suzuki polycondensation in aqueous systems has proven to be a versatile method, which has been applied to the synthesis of various polymer types ]234]. 

An excellent example of the use of Suzuki polycondensation is the synthesis of ladder-type PPPs (67) (see Scheme 6.16) [84]. A precursor polymer 79 is prepared by AA-BB coupling and then converted to the ladder polymers by polymer analogous reactions. Reduction followed by ring closure with boron trifluoride produces a polymer (67a) with bridgehead hydrogens, while addition of methyl lithium instead of reduction leads to Me-LPPP (67b) with methyls at the bridgeheads. 

Scheme 6.15 Suzuki polycondensation by AB (above) and AA-BB (below) methods.

Sakamoto, J., Rehahn, M., Wegner, G., SchlQter, A.D., 2009. Suzuki Polycondensation Polyarylenes a la Carte. Macromol Rapid Commun. 30,653-687. 

Suzuki polycondensation (SPC) uses Suzuki cross-coupling (SCC), which has been described in detail including all mechanistic aspects in Part ni.2.2. It is a step-growth... 

FIGURE 3.21 Synthesis of polyarylenes via C—C coupling by A +B Stille and Suzuki polycondensation (Mj, Mj=arene like phenyl). 

P23/25 (with a fourth generation of dendrons) from a low-molecular-weight monomer 23 and macromonomer 26, following a Suzuki polycondensation protocol. 

P 25 and 125 [according to gel-permeation chromatography (GPC) on a gram scale]. Although the actual molar mass of this polymer is still unclear, these data clearly show that Suzuki polycondensation can function even for sterically enormously loaded G4 monomers. 

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