Use of the Extended One-Pot (EOP) Procedure for the Preparation of Ethynylated Thiophene Derivatives and Related Palladium-Ethynylthiophene Organometallic Oligomers Patrizia Altamura,* ,† Giorgio Giardina, ‡ Claudio Lo Sterzo,* ,‡,⊥ and Maria Vittoria Russo § Dipartimento di Chimica, Universita ` di Salerno, Via S. Allende, 84081 Baronissi, Italy, and Centro CNR di Studio sui Meccanismi di Reazione and Dipartimento di Chimica, Universita ` “La Sapienza”, Box 34-Roma 62, Piazzale Aldo Moro, 5, 00185 Roma, Italy Received April 17, 2001 The palladium-catalyzed coupling (Stille coupling) of 2,5-diiodothiophene (1) with tributyl- (ethynyl)tin forms the 2,5-bis(ethynyl)thiophene (3) and tributyltin iodide as side product (step 1). Addition of lithium diisopropylamide (LDA) to this mixture causes deprotonation of the bis-alkyne and its reaction with the tin halide present in the medium to form the 2,5-bis[(tributyltin)ethynyl]thiophene (4) (step 2). To this mixture was subsequently added trans-dichlorobis(tri-n-butylphosphine)palladium (5), and the corresponding trans-bis(tri- n-butylphosphine)-μ-[2,5-bis(ethynyl)thiophene]palladium oligomer (6) was obtained (step 3). Alternatively, the same route can be directed toward the formation of ethynylated thiophene oligomers: after formation of the 2,5-bis[(tributyltin)ethynyl]thiophene (4) (step 2), addition of 2-iodothiophene (8) or 2-iodo-5-(trimethylsilyl)thiophene (10) led to the formation of 2,5-bis(2-thienylethynyl)thiophene (9) (step 3) and [2-trimethylsilyl(ethynyl)- thiophene]-2,5-bisethynylthiophene (11) (step 3′), respectively. The latter can be easily desilylated to obtain the [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13), while treatment of 9 with sec-BuLi/I 2 formed the 2,5-[2,2′-(5,5′-diiodo)bisthienyl]bisethynylthiophene (12). Through a sequence of transformations similar to steps 1-3, the oligo(iodo)ethynylthiophene 12 has been connected to the bis(tri-n-butylphosphine)palladium moiety to form the trans- bis(tri-n-butylphosphine)-μ-[2,2′-bis(ethynyl)thiophene]-2,5-bisethynylthiophene]palladi- um polymer (15). To compare the advantages of the above extended one-pot (EOP) procedures over classical routes, polymers 6 and 15 were also prepared by the copper-catalyzed reaction of trans-dichlorobis(tri-n-butylphosphine)palladium (5) with 2,5-bis(ethynyl)thiophene (3) and [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13). Introduction Organometallic polymers having a backbone com- posed of conjugated polyynes and transition metals are attracting increasing attention in material science because they may exhibit liquid crystalline, 1 magnetic, 2 optical, 3 and electronic properties. 4 These technologi- cally important characteristics arise from the unique electronic delocalization in these materials along the entire polymer backbone, including metal atoms and bridging acetylide spacers. Because of these important potential applications, efficient routes to organometallic conjugated polymers are required. Preparation of polymeric materials of type [-CtC- M-CtC-Ar-] n (M ) Ni, Pd, Pt) was first developed by Hagihara 5 by means of a dehydrohalogenation reac- tion using Cu-catalyzed coupling of terminal alkynes (H-CtC-Ar-CtC-H) and transition metal halides (L 2 MCl 2 ). Although this procedure is quite efficient and has also allowed the preparation of polymers containing mixed metals into the polymer backbone, 5c this synthetic route suffers from a major drawback of preparing and handling pure terminal alkynes, which are quite reac- tive materials, occasionally manifesting uncontrollable reactivity. 6 Terminal alkynes are also used for the preparation of polymers containing Pt-Pt bonds, and gold-containing polymers obtained by Puddephatt; 7 the * Corresponding authors. † Universita ` di Salerno. ‡ Centro CNR di Studio sui Meccanismi di Reazione, Universita ` “La Sapienza”. § Dipartimento di Chimica, Universita ` “La Sapienza”. ⊥ E-mail: Claudio.Losterzo@uniroma1.it. (1) Takahashi, S.; Takai, Y.; Morimoto, H.; Sonogashira, K.; Hagi- hara, N. Mol. Cryst. Liq. Cryst. 1982, 32, 139. (2) (a) Posselt, D.; Badur, W.; Steiner, M.; Baumgarten, M. Synth. Met. 1993, 55-57, 3299. (b) Hmyene, M.; Yassar, A.; Escorne, M.; Percheron-Guegan, A.; Garnier, F. Adv. 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