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  • Publication
    Accès libre
    Mono and dinuclear rhodium, iridium and ruthenium complexes containing chelating 2,2′-bipyrimidine ligands: Synthesis, molecular structure, electrochemistry and catalytic properties
    (2007)
    Govindaswamy, Padavattan
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    Canivet, Jérôme
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    ; ;
    Štěpnička, Petr
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    Ludvík, Jiří
    The mononuclear cations [(η5-C5Me5)RhCl(bpym)]+ (1), [(η5-C5Me5)IrCl(bpym)]+ (2), [(η6-p-PriC6H4Me)RuCl(bpym)]+ (3) and [(η6-C6Me6)RuCl(bpym)]+ (4) as well as the dinuclear dications [{(η5-C5Me5)RhCl}2 (bpym)]2+ (5), [{(η5-C5Me5)IrCl}2 (bpym)]2+ (6), [{(η6-p-PriC6H4Me)RuCl}2 (bpym)]2+ (7) and [{(η6-C6Me6)RuCl}2 (bpym)]2+ (8) have been synthesised from 2,2′-bipyrimidine (bpym) and the corresponding chloro complexes [(η5-C5Me5)RhCl2]2, [(η5-C5Me5)IrCl2]2, [(η6-PriC6H4Me)RuCl2]2 and [(η6-C6Me6)RuCl2]2, respectively. The X-ray crystal structure analyses of [3][PF6], [5][PF6]2, [6][CF3SO3]2 and [7][PF6]2 reveal a typical piano-stool geometry around the metal centres; in the dinuclear complexes the chloro ligands attached to the two metal centres are found to be, with respect to each other, cis oriented for 5 and 6 but trans for 7. The electrochemical behaviour of 1–8 has been studied by voltammetric methods. In addition, the catalytic potential of 1–8 for transfer hydrogenation reactions in aqueous solution has been evaluated: All complexes catalyse the reaction of acetophenone with formic acid to give phenylethanol and carbon dioxide. For both the mononuclear and dinuclear series the best results were obtained (50 °C, pH 4) with rhodium complexes, giving turnover frequencies of 10.5 h−1 for 1 and 19 h−1 for 5.
  • Publication
    Accès libre
    Synthesis, structure and electrochemistry of cationic diruthenium complexes of the type [(N∩N)2Ru2 (CO)2 (μ-CO)2(μ-OOCFc)]+ containing a ferrocenecarboxylato bridge and two chelating aromatic diimine ligands
    (2007)
    Auzias, Mathieu
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    ; ;
    Štěpnička, Petr
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    Ludvík, Jiří
    The dinuclear bis(ferrocenecarboxylato) complex Ru2 (CO)4 (μ-OOCFc)2 (py)2 (Fc = ferrocenyl, py = pyridine) was found to react with aromatic diimines (2,2′-dipyridyl, 4,4′-dimethyl-2,2′-dipyridyl, 1,10-phenanthroline, 5-nitro-1,10-phenanthroline, and 5-amino-1,10-phenanthroline) in methanol to give the cationic diruthenium complexes [(N∩N)2Ru2 (CO)2 (μ-CO)2(μ-OOCFc)]+ (1: N∩N = 2,2′-dipyridyl, 2: N∩N = 4,4′-dimethyl-2,2′-dipyridyl, 3: N∩N = 1,10-phenanthroline, 4: N∩N = 5-nitro-1,10-phenanthroline, 5: N∩N = 5-amino-1,10-phenanthroline), which have been isolated as the hexafluorophosphate salts. The molecular structure of 3, solved by single-crystal X-ray analysis of the tetraphenylborate salt [3][BPh4], shows a diruthenium backbone bridged by two carbonyl and by one ferrocenecarboxylato ligand, the two 1,10-phenanthroline ligands being in the axial positions. Cyclic voltammetry in dichloromethane reveals for all compounds two successive oxidations due to ferrocene/ferrocenium redox couple and oxidation of the diruthenium core.
  • Publication
    Accès libre
    Mono and dinuclear iridium, rhodium and ruthenium complexes containing chelating carboxylato pyrazine ligands: Synthesis, molecular structure and electrochemistry
    (2007)
    Govindaswamy, Padavattan
    ;
    ; ;
    Štěpnička, Petr
    ;
    Ludvík, Jiří
    The mononuclear complexes [(η5-C5Me5)IrCl(L1)] (1), [(η5-C5Me5)RhCl(L1)] (2), [(η6-p-PriC6H4Me)RuCl(L1)] (3) and [(η6-C6Me6)RuCl(L1)] (4) have been synthesised from pyrazine-2-carboxylic acid (HL1) and the corresponding complexes [{(η5-C5Me5)IrCl2}2], [{(η5-C5Me5)RhCl2}2], [{(η6-p-PriC6H4Me)RuCl2}2], and [{(η6-C6Me6)RuCl2}2], respectively. The related dinuclear complexes [{(η5-C5Me5)IrCl}2 (μ-L2)] (5), [{(η5-C5Me5)RhCl}2 (μ-L2)] (6), [{(η6-p-PriC6H4Me)RuCl}2 (μ-L2)] (7) and [{(η6-C6Me6)RuCl}2 (μ-L2)] (8) have been obtained in a similar manner from pyrazine-2,5-dicarboxylic acid (H2L2). Compounds isomeric to the latter series, [{(η5-C5Me5)IrCl}2 (μ-L3)] (9), [{(η5-C5Me5)RhCl}2 (μ-L3)] (10), [{(p-PriC6H4Me)RuCl}2 (μ-L3)] (11) and [{(η6-C6Me6)RuCl}2 (μ-L3)] (12), have been prepared by using pyrazine-2,3-dicarboxylic acid (H2L3) instead of H2L2. The molecular structures of 2 and 3, determined by X-ray diffraction analysis, show the pyrazine-2-carboxylato moiety to act as an N,O-chelating ligand, while the structure analyses of 5–7, confirm that the pyrazine-2,5-dicarboxylato unit bridges two metal centres. The electrochemical behaviour of selected representatives has been studied by voltammetric techniques.