Luminescent Materials DOI: 10.1002/ange.200901226 9,10-Dihydro-9,10-diboraanthracene: Supramolecular Structure and Use as a Building Block for Luminescent Conjugated Polymers** Andreas Lorbach, Michael Bolte, Haiyan Li, Hans-Wolfram Lerner, Max C. Holthausen,* Frieder Jäkle,* and Matthias Wagner* The use of organoboranes in preparative chemistry has been established for decades. [1] In contrast, research on boron- containing materials is still at an early stage, but numerous exciting perspectives are already emerging. [2–6] The incorpo- ration of boron into conjugated p systems leads to similar electronic states as oxidative doping but gives neutral materials because of the isoelectronic relationship between three-coordinate boron atoms and carbocations. Moreover, the ability of boron atoms to form Lewis acid–base pairs and thereby to disrupt the p-conjugation pathway can be exploited for the development of molecular switches because adduct formation is reversible in many cases. Among the multiple applications that can be envisaged for boron-doped macromolecules, their use in organic light- emitting devices (OLEDs) holds particular promise, since properly designed organoboranes are useful not only as electron transporters but also as light emitters. [7–10] The realization that classical inorganic solid-state materials can be replaced by lightweight and highly tunable organoelement compounds has sparked a vibrant interest in the subject, as well as an intense quest for novel and stable boron-containing functional groups. One focus of our research is conjugated polymers that contain three-coordinate boron atoms as integral parts of their main chain and exhibit photo- or electroluminescent behavior (see Refs. [11–14] for examples of lumi- nescent polymers with boron-func- tionalized side chains). To date, only a few synthetic pathways to such compounds have been developed, for example polycondensation approaches [15–20] and the hydrobora- tion polymerization. [21–24] Chujo and co-workers have reported that the hydroboration of (hetero)aromatic diynes with mesitylborane leads to stable p-conjugated organoboron polymers A (Scheme 1). [21, 22] Depending on the nature of the arenediyl bridge, these compounds exhibit strong green, blue, and even white photoluminescence. However, a possible disadvantage of the mesi- tylborane component lies in the fact that both reactive hydrogen atoms are attached to the same boron atom. As a result, the first hydroboration event (MesBH 2 + HCCR! MesB(H)R’) occurs under steric and electronic conditions that are significantly different to those of the second addition reaction (MesB(H)R’ + HCCR !MesBR’ 2 ; R’ = C(H)C(H)R). An alternative might be the choice of appro- priate ditopic derivatives B with two spatially separated but chemically related H  B functionalities (Scheme 1). We came to the conclusion that the following conditions should be met when considering the design of suitable candidates: 1) the ditopic building block itself should already possess an extended p-conjugated electron system, 2) a rigid framework guarantees maximum p overlap between the boron atoms and the aromatic substituents, and 3) a cyclic structure should be more stable than an open-chain deriva- tive. We report herein the realization of this concept, that is, the successful synthesis of 9,10-dihydro-9,10-diboraanthra- cene ((2) n ; Scheme 2). Compound (2) n possesses an unpre- cedented polymeric solid-state structure and exhibits high reactivity towards terminal alkynes. We therefore propose this compound as a highly attractive building block for the preparation of both molecular and polymeric organoboron materials. Scheme 1. Hydrobora- tion polymerization of (hetero)aromatic diynes with mesitylbor- ane to give neutral boron-doped materials A ; schematic represen- tation of ditopic di- organoboranes B. Mes = mesityl. [*] Dipl.-Chem. A. Lorbach, Dr. M. Bolte, Dr. H.-W. Lerner, Prof. Dr. M. C. Holthausen, Prof. Dr. M. Wagner Institut für Anorganische Chemie, Goethe-Universität Frankfurt Max-von-Laue-Strasse 7, 60438 Frankfurt am Main (Germany) Fax: (+ 49) 69-798-29260 E-mail: max.holthausen@chemie.uni-frankfurt.de matthias.wagner@chemie.uni-frankfurt.de H. Li, Prof. Dr. F. Jäkle Department of Chemistry, Rutgers University Newark 73 Warren Street, Newark, NJ 07102 (USA) E-mail: fjaekle@andromeda.rutgers.edu [**] A.L. thanks the Fonds der Chemischen Industrie for a Ph.D. grant. F.J. thanks the NSF (CHE-0809642) and the Alexander von Humboldt Foundation for a Friedrich Wilhelm Bessel Research Award. This work was supported by the Deutsche Forschungsge- meinschaft, the Chemetall GmbH, and the City Solar AG, Bad Kreuznach. Supporting information for this article (experimental procedures, X- ray crystal structure analysis of 3, photophysical characterization of 8, MALDI-TOF spectrum of 8, and the results of quantum chemical calculations on monomeric 2, the monoadduct 2·pyridine, and the diadduct 3 in syn and anti configuration) is available on the WWW under http://dx.doi.org/10.1002/anie.200901226. CCDC 708349 ((2) n ) and 708348 (3) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif. Zuschriften 4654  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2009, 121, 4654 –4658