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Polynuclear Organometallic Helices by Means of Novel Coupling Reactions of Cyclomanganated Complexes with Aryl-Substituted Diazoalkanes:  Syntheses of New Manganospiralenes and Appended (η5-fluoren-9-yl)M(CO)3 Complexes (M = Mn, Re)

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journal contribution
posted on 23.07.2002, 00:00 by Christophe Michon, Jean-Pierre Djukic, Zoran Ratkovic, Jean-Paul Collin, Michel Pfeffer, André de Cian, Jean Fischer, Dirk Heiser, Karl Heinz Dötz, Martin Nieger
Novel reactions of various cis-(LC)Mn(CO)4 complexes (LC = a three-electron chelating ligand) with diazodiphenylmethane and 9-diazofluorene allowed the synthesis of a new type of oligomeric polynuclear manganospiralene derived from quinoxaline and the ready preparation of a new class of appended (η5-fluorenyl)Mn(CO)3 complexes. Hence, bis-cyclomanganated 2,3-diphenylquinoxaline cleanly reacted to afford a dinuclear dispiralene in which the heterocycle is embedded between two phenyl rings introduced by diphenyldiazomethane. The reaction of cyclomanganated and rhenated aromatic compounds with 9-diazofluorene is shown to proceed efficiently under thermolytic conditions, which promote the departure of one molecule of CO and the subsequent coordination of a fluorenylidene fragment. Further rearrangements consisting of a cis-migration step and of a series of haptotropic shifts lead to the final appended (η5-fluorenyl)M(CO)3 complex (M = Mn, Re). This new C−C bond-forming reaction has enabled the synthesis of a pentacyclic helical compound derived from bis-cyclomanganated 2,3-diphenylquinoxaline and whose conformation could be locked by coordination to Ag+, affording a hybrid inorganic−organometallic polyhelix. An overview of the electrochemical properties of selected mono- and binuclear spiralenes is disclosed and shows that most spiralenes display electrochemically reversible reduction processes. An ESR analysis of the radical anion of a dinuclear spiralene indicated that the reduction process is ligand-centered and the spin density essentially located at the heterocycle. The structures of new spiralenes and appended (fluorenyl)M(CO)3complexes, obtained by crystal X-ray diffraction techniques, are described.