Journal of Molecular Catalysis A: Chemical 195 (2003) 125–131 Palladium-catalyzed synthesis of oligo(alkylthiophenes) Jwanro Hassan, Emmanuelle Schulz, Christel Gozzi, Marc Lemaire ∗ Laboratoire de Catalyse et Synthèse Organique, UMR 5622, UCBL, CPE, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France Received 15 July 2002; accepted 26 September 2002 Abstract A new palladium-catalyzed polymerization of 2-bromo-3-octylthiophene is described giving rise to oligo(3-octylthiophenes) with good yields. A study was carried out in order to optimize the polymer regioregularity (reaching 90%) and to increase the molecular weight (up to dodecamers). A mechanism is proposed with a coordination between palladium and sulfur, in a modified Heck mechanism. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Heck-type polymerization; Oligo(alkylthiophenes); Palladium acetate; Conducting polymers 1. Introduction The search and development for new ordered ma- terials is an important field of interest for synthetic chemists. Poly(3-alkylthiophenes) have been partic- ularly studied, as the most significant class of con- jugated polymers [1]. They are thermodynamically stable and have been used as materials for many appli- cations, such as light-emitting devices [2,3] and thin film transistors [4]. The physical properties depend on the nature and the regioregularity of the polymers. Polythiophenes were synthesized either by oxida- tive electrochemical or chemical polymerization or by organometallic couplings [5]. Sugimoto et al. [6] have developed a chemical polymerization implying the monomer oxidation by iron trichloride, leading to high-molecular-weight polymers. Nevertheless, this method requires an over stoichiometric amount of iron trichloride and generates a large quantity of ∗ Corresponding author. Tel.: +33-4-7243-1407; fax: +33-4-7243-1408. E-mail address: marc.lemaire@univ-lyon1.fr (M. Lemaire). effluents. McCullough et al. [7] have reported the synthesis of regioregular polythiophenes. By using a Kumada–Corriu coupling, the homo- polymerization of 2-bromo-5-(bromomagnesio)-3- alkylthiophenes was carried out in the presence of a catalytic amount of Ni(II). Rieke and co-workers [8] have also used a catalytic amount of Ni(II) in the poly- merization of 2-bromo-3-alkyl-5-(iodozincio)-thio- phenes. Iraqi and Barker [9] performed a Stille coupling for the polymerization of 2-iodo-3-alkyl-5- tri-n-butylstannyl-thiophenes. More recently, this re- action has been optimized by Lère-porte et al. [10], higher-molecular-weight polymers were obtained. Bidan and Guillerez [11] have synthesized regioregu- lar polythiophenes using the Suzuki coupling for the polymerization of 2-iodo-3-alkyl-5-thienyl-boronic esters. Regioregular and high-molecular-weight poly- mers were thus obtained by the above-described coupling methods. The main drawbacks of these syn- theses are the use of organometallic reagents which are often dangerous and/or toxic, and the requirement of monomers with high purity to allow the preparation of regular polymers. 1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S1381-1169(02)00543-5