Published: July 26, 2011 r2011 American Chemical Society 4325 dx.doi.org/10.1021/om2003943 | Organometallics 2011, 30, 4325–4329 ARTICLE pubs.acs.org/Organometallics Cross-Coupling of 5,11-Dibromotetracene Catalyzed by a Triethylammonium Ion Tagged Diphenylphosphine Palladium Complex in Ionic Liquids Antonio Papagni, † Claudio Trombini, ‡ Marco Lombardo,* ,‡ Stefano Bergantin, † Amani Chams, § Michel Chiarucci, ‡ Luciano Miozzo,* ,†,§ and Matteo Parravicini † † Scienza dei Materiali, Universita degli Studi di Milano Bicocca, Via R. Cozzi 53, 20125 Milano, Italy ‡ Dipartimento di Chimica “G. Ciamician”, Universita degli Studi di Bologna, via Selmi 2, 40126 Bologna, Italy § ITODYS, Cnrs-Umr 7086, Universite Paris Diderot, 15 rue Jean Antoine de Baïf, 75205 Paris Cedex 13, France b S Supporting Information ABSTRACT: Suzuki Miyaura cross-coupling reactions of 5,11-dibromotetracene with arylboronic acids, using a triethylammonium-tagged palladium(II) diphenylphosphine complex as catalyst in a pyrrolidinium-based ionic liquid (IL), allowed the preparation of new 5,11-diaryl-substituted tetracenes in good to excellent yields. The synthesis of the new 5,11-diboronic-tetracene bis-pinacolate ester and its use in Suzuki Miyaura cross-coupling reaction with aryl bromides in IL are also reported. T etracene, pentacene, and their derivatives are among the most studied molecular organic semiconductors. 1 A large number of substituted acenes have been reported and used, for example, for organic light-emitting diodes, field-effect tran- sistors, and solar cells. 2 Among them, substituted tetracenes, such as 5,6,11,12-tetraphenyltetracene (rubrene) and 5,11- dichlorotetracene, 3 show very high charge mobilities. Indeed, rubrene represents the state of the art in this field, showing exceptional charge carrier mobility values up to 20 cm 2 /(V s). The origin of these outstanding mobility values has been ascribed to a favorable crystal packing, 4 even though deeper investiga- tions, aimed at understanding the origin of the electronic proper- ties of these organic semiconductors, are in progress. Within this framework, the improvement of mobility values is based on the tuning both of electronic properties at the molecular level and of the crystal packing, by acting on the nature of the substituents present on the tetracene backbone. Unfortunately, few protocols for the synthesis of substituted acenes are described in the literature. They are traditionally based on multistep aryllithium addition to naphthacenediones and Diels Alder-based reac- tions, whose low yields and lack of generality are a limitation to the preparation of a wide spectrum of derivatives. 5 This is particularly true for 5,11-diaryl-substituted tetracenes, and to the best of our knowledge, only the syntheses of 5,11-diphenyl- and 5,11-ditolyltetracene are reported in the literature, 6 while the preparation of 5,11-dinaphthyltetracene is claimed in a recent patent. 7 Although cross-coupling procedures look very attractive as a general synthetic protocol for substituted tetracenes, 8 only recently the synthesis of substituted tetracenes has been report- ed via a Kumada Corriu cross-coupling reaction between the 5,6,11,12-tetrachlorotetracene and methylmagnesium chloride, 9 and using a Suzuki Miyaura cross-coupling reaction between the 5,11-dibromotetracene and a perylene-based boronic deriv- ative. 10 This is quite surprising, since a Suzuki Miyaura cross- coupling reaction is particularly appealing, 11 due to the wide commercial availability of stable boronic acids and esters, the mild conditions required, and the high tolerance toward func- tional groups. The difficulties related to the availability of iodo- and bromoacenes and their low reactivity for steric demands when the halides are at the 5-, 6-, 11-, and 12-positions partially justify the scarce use of these substrates in transition-metal- mediated cross-coupling reactions. Recently, an effective protocol for the Suzuki Miyaura cross coupling in ionic liquids (ILs) has been developed, where the ionic phosphine 1 (Scheme 1) acts as the palladium ligand (L). 12 Received: May 13, 2011