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ABSTRACT: Five different types of β-diketiminate ligands, bearing electron-donating to strongly electron-withdrawing substituents, were synthesized and used in the synthesis of Cp* ruthenium complexes (Cp* = η5-C5Me5). One series consists of complexes with a covalent RuIII–Cl bond, and the other series features a reduced RuII center, where the chloride is abstracted by treatment of the corresponding RuIII compounds with Zn or Mg. All compounds were characterized by single-crystal X-ray diffraction, UV–visible spectroscopy, and cyclic voltammetry. In the case of RuII complexes, solution NMR techniques provided key information regarding the electronic and structural differences induced by the different β-diketiminate ligands employed. Capitalizing on the facile reduction–oxidation cycle of the Cp* ruthenium β-diketiminato complexes, catalytic atom transfer radical addition (ATRA) and cyclization (ATRC) reactions were performed on relevant substrates. The turnover rates are strongly dependent on the type of β-diketiminate used, where ligands with electron-withdrawing substituents, i.e., trifluoromethyl groups, provided complexes that efficiently catalyze the addition of CCl4 or toluenesulfonyl chloride to styrene. In contrast, complexes with electron-donating substituents on the β-diketiminate promoted efficient ATR cyclization of N-allyl-N-phenyltrichloroacetamide and 2,2,2-trichloroethyl ether. Thus, the overall product conversion and yield are dependent on matching the ligand substitution pattern of the catalyst to the type of substrate.
10/2011;
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ABSTRACT: In organic synthesis, cyclopropanation reactions are often performed with Simmons-Smith-type reagents or by transition metal catalyzed reactions of olefins with diazo compounds. A novel method for the synthesis of substituted cyclopropanes is described that is based on a two-step reaction sequence. Olefins are reacted with 1,1'-dichlorides in a Ru-catalyzed atom transfer radical addition (ATRA) process and the resulting 1,3-dichlorides are directly converted into cyclopropanes by reductive coupling with magnesium. This one-pot procedure is applicable to a variety of substrates and can be performed in an inter- or intramolecular fashion.
CHIMIA International Journal for Chemistry 01/2010; 64(3):188-90. · 1.21 Impact Factor
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ABSTRACT: Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom-transfer radical reactions catalyzed by the complexes [RuCl2Cp*(PPh3)] and [RuClCp*(PPh3)2] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero-order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate-limiting step of the reaction.
Chemistry 09/2009; 15(43):11601-7. · 5.93 Impact Factor
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Angewandte Chemie International Edition 09/2009; 48(43):8115-9. · 13.45 Impact Factor
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ABSTRACT: A new catalytic procedure for atom-transfer radical addition (ATRA) and cyclization (ATRC) reactions is described. The combination of the ruthenium(III) complex [RuCl(2)Cp*(PPh3)] (Cp*: pentamethylcyclopentadienyl) with magnesium allows these reactions to be performed under mild conditions with high efficiency. In most cases, the catalyst concentrations required are significantly lower than those used in previously reported procedures. It is suggested that magnesium acts as a reducing agent that generates and regenerates the catalytically active ruthenium(II) species. The precatalyst [RuCl(2)Cp*(PPh3)] has been analyzed by X-ray crystallography.
Chemistry 02/2007; 13(24):6899-907. · 5.93 Impact Factor
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ABSTRACT: The combination of the air-stable RuIII complex [Cp*RuCl2(PPh3)] with AIBN can be used to catalyze the atom transfer radical addition reactions of polychlorinated compounds and of sulfonyl chlorides to olefins with unprecedented turnover numbers of up to 44 000.
Journal of the American Chemical Society 07/2006; 128(23):7440-1. · 9.91 Impact Factor
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ABSTRACT: Sequential intermolecular atom transfer radical addition reactions of activated dichlorides Cl2CRR′ (R = CN, CO2Et, R′ = H, CN, CO2Et) with two olefins catalyzed by [Cp*RuCl2(PPh3)] in the presence Mg allow the synthesis of linear 1,5-dichlorides. Different olefins can be employed in the first and in the second addition reaction. The reaction products are interesting synthetic precursors as demonstrated by the synthesis of two cyclopentanes by Mg-induced dechlorination. The structure of trans-3,4-diphenylcyclopentanecarbonitrile was determined by single-crystal X-ray diffraction.
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ABSTRACT: The catalytic activity of [Cp*OsBr2(PPh3)] in conjunction with Mg has been evaluated for atom transfer radical addition (ATRA) and cyclization (ATRC) reactions. The Os complex enabled these reactions to be performed with similar efficiency as that of the analogous Ru complex [Cp*RuCl2(PPh3)]. The olefin complex [Cp*OsBr(H2C=CHPh)(PPh3)] was obtained by reduction of [Cp*OsBr2(PPh3)] with Mg in the presence of an excess of styrene, whereas an analogous Ru complex was not observed. Kinetic investigations suggest that olefin complexes of Os can form under catalytic conditions.
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