Metal catalyzed cross-coupling polymerizations

H NMR studies have shown that metal-catalyzed cross-coupling polymerizations of 3-alkylthiophenes such as reactions 6.4, generally lead to regiorandom polythiophenes. A similar situation holds for polymerizations performed by the oxidation... 

MW and PDl of semiconducting polymers have become a popular topic for many research groups [35,44,59,60,88,101]. Commercially available HT-PHTs synthesized by metal-catalyzed cross-coupling polymerization have a broad PDl (>2.0),... 

Synthesis of a poly[tetra(2,3-thienylene)] P4.16 was realized by typical Ni°-catalyzed cross-coupling polymerization of metalated tetramer 4.16, which in turn was prepared effectively from quaterthiophene 4.15 by oxidative coupling in 48% yield (Scheme 1.37) [366, 367]. The polymer, a poly( [8]annulene), which was soluble in organic solvents due to the butyl side-chains, showed electronic properties typical for polythiophenes a measurement of actuation, however, could not be obtained. 

The polymerizations described in Figs. 9.9 and 9.11 use a metal-catalyzed cross-coupling technique that has been investigated extensively [67-73]. The reaction is believed to proceed by (1) oxidative addition of an organic halide with a metal-phosphine catalyst, (2) transmetalla-tion between the catalyst complex and a reactive organo-... 

The elimination of a hydrogen atom positioned on a carbon to the central metal constimtes an important reaction in transition metal catalysis. In the classical example, an alkylmetal intermediate is reversibly converted to an alkene and a metaUiydride (scheme 1.12). Despite the fact, that the resulting hydridometal complex can be exploited in various catalytic processes including polymerization reactions, [57] cycloisomerizations, [58] annulations, [59] etc., the ]S-hydride elimination is often considered undesired in transition metal catalyzed cross couplings. Thus, efforts have often been concentrated towards the prohibition of this fundamental reaction [60]. Nevertheless, the ]S-hydride elimination is a vital transformation in a number of catalytic processes including the ene-yne coupling reported by Trost [61] and Skrydstrup, [62] oxidation of alcohols, [63] the Heck reaction etc [64]. 

Oxidative dimerization by treating thienyllithium with copper(II) chloride was reported in CHEC-I. This method has found application in the synthesis of polythiophenes attached to crown ethers these compounds exhibit selective response to alkali-metal ions and can therefore function as sensors. An example of the synthesis is given in Equation (57) <93JA12214>. The monomer (589) was converted to the 5,5 -dilithiated derivative and then polymerized either by direct reaction with Fe(acac)3 or by conversion to the tin derivative followed by Pd-catalyzed cross-coupling (see Section 2.10.4.7.3). 

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