Wittig polycondensation

In the effort to make pure blue-emitting materials Shim and coworkers [146] synthesized a series of PPV-based copolymers containing carbazole (polymers 95 and 96) and fluorene (polymers 97 and 98) units via Wittig polycondensation. The use of trimethylsilyl substituents, instead of alkoxy groups, eliminates the electron donor influence of the latter and leads to chain distortion that bathochromically shifts the emission (Amax = 480 nm for 95 and 495 nm for 97). In addition, a very high PLQY was found for these polymers in the solid state (64 and 81%, respectively). Single-layer PLEDs fabricated with 95 and 97 (ITO/polymer/Al) showed EL efficiencies of 13 and 32 times higher than MEH-PPV, respectively (see also Ref. [147] for synthesis and PLED studies of polymers 99 and 100) (Chart 2.20). 

Wittig polycondensation route has been widely used for the preparation of alternating copolymers in which carbonyl compounds such as aldehyde and ketone are... 

Wittig-Type and Wittig-Horner-Type Polycondensations Polymers... 

A second example of step-growth polycondensations with formation of the ole-finic double-bond are Wittig- and Wittig-Horner-type condensations. The Wittig-type polycondensations involve AA/BB-type reactions of aromatic bisal-dehydes with bisphosphonium ylides [99,100] with formation of PPV derivatives (75) and lead to products of only moderate molecular weight (DP 10-20). 

Typically, in the Knoevenagel polycondensation, a terephthalic aldehyde is condensed with a bis-(cyanomethyl)-benzene compound. Since two monomers are used, PPVs with a strictly alternating structure can be synthesized. The Knoevenagel polycondensation allows the convenient synthesis of compounds in that the backbone double bond is substituted. PPV modified with cyano groups show a high EL activity. The synthesis is shown in Figure 3.8. In a quite similar way, PPV can be formed by the Wittig... 

Scheme 4.5 shows the most important direct routes for preparing soluble PAVs Heck coupling, and Wittig and Horner polycondensations. The two biggest advantages of these routes are that they avoid the formation of tolane and other defects seen in the precursor routes, and also that they allow the synthesis... 

A polymer, incorporating both TPD and phenylenevinylene segments (31) has by recently reported [171]. This polymer possesses excellent film-forming properties, good thermal stability, and high electrochemical reversibility. It was prepared by the Wittig-Horner polycondensation reaction between a TPD-based dialdehyde and 1,4-xylylene diphosphate. 

Some drawbacks of the precursor routes mentioned above have been overcome by the use of polycondensation- and C-C-bond-coupling reactions. To produce soluble PPV-, poly(thiophene)-, or poly(pyrrol) derivatives for spin coating preparation, various types of transition metal catalyzed reactions, such as the Heck-, Suzuki-, and Sonogashira-reaction, Wittig- and Wittig-Horner-type coupling reactions, or the McMurry- and Knoevenagel-condensation have been utilized. 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

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