Synthesis Using Nickel or Palladium Complexes

One of the most useful methods of chemical synthesis is the Ni-catalyzed dehalogenation polycondensation of dihaloaromatic compounds [271]  

Fluoroalkylated heteroaromatic polymers can be prepared from 2,5-dibromo-3-perfluoropropylthiophene with NiCl2 [567]. The cross coupling reaction of dihaloheteroaromatic compounds and l,2-bis(tributylstannyl)ethylene catalyzed with palladium complexes leads in a single step to poly(thienylene vinylene) [353,568, 569]. The synthesis of structurally homogeneous PATs is described in Sect. 5.1.8. 

Zero-Valent Nickel Complexes. A new polycondensation reaction uses the zero-valent nickel complex itself as the dehalogenation reagent [271,570,571]  

As zero-valent nickel complexes, mixtures of bis(l,5-cyclooctadiene)nickel and neutral ligands L have been employed. This polycondensation affords PT and PAT with relatively well-defined linkages between the monomer units in the polymer chains in high yields [92,266,271,272,571]. Vacuum deposition of PT gives crystalline films with their main chains essentially perpendicular to the surface of substrates such as carbon and gold [266]. The iodine-doped PT reaches an electrical conductivity of 8Scm and the FeCls-doped PT an electrical conductivity of 0.5 S cm [272]. 

For the preparation of PAT (n = 1,6, 8,12) and of poIy(3-cyanothiophene) with high yields, a zero-valent nickel complex is also used [266]. Hexyl substituted oligo(thiophene)s (number of thiophene rings 6,9,12,15) can be prepared by the Ni(0)-catalyzed coupling reaction of a 5,5 -dibromo-3,3 -dihexyl-2,2 5, 2 -terthiophene) [572, 573]. PT derivatives having alkyloxy substituents at 3 positions are synthesized by dehalogenation polycondensation of the corresponding 2,5-dibromothiophene derivatives with zero-valent nickel complexes [247], 

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