- Nickel-Catalyzed Formation of 1,3-Dienes via a Highly Selective Cross-Tetramerization of Tetrafluoroethylene, Styrenes, Alkynes, and Ethylene
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In the presence of a catalytic amount of Ni(cod)2 (cod = 1,5-cyclooctadiene) and PCy3 (Cy = cyclohexyl), the cross-tetramerization of tetrafluoroethylene (TFE), alkynes, and ethylene occurred in a highly selective manner to afford a variety of 1,3-dienes with a 3,3,4,4-tetrafluorobutyl chain. In addition, a Ni(0)-catalyzed cross-tetramerization of TFE, alkynes, ethylene, and styrenes was developed. These catalytic reactions might proceed via partially fluorinated five- and seven-membered nickelacycle key intermediates.
- Kawashima, Takuya,Ohashi, Masato,Ogoshi, Sensuke
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supporting information
p. 17795 - 17798
(2017/12/26)
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- Combined experimental and theoretical study on the reductive cleavage of inert C-O bonds with silanes: Ruling out a classical Ni(0)/Ni(II) catalytic couple and evidence for Ni(I) intermediates
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A mechanistic and computational study on the reductive cleavage of C-OMe bonds catalyzed by Ni(COD)2/PCy3 with silanes as reducing agents is reported herein. Specifically, we demonstrate that the mechanism for this transformation does not proceed via oxidative addition of the Ni(0) precatalyst into the C-OMe bond. In the absence of an external reducing agent, the in-situ-generated oxidative addition complexes rapidly undergo β-hydride elimination at room temperature, ultimately leading to either Ni(0)-carbonyl- or Ni(0)-aldehyde-bound complexes. Characterization of these complexes by X-ray crystallography unambiguously suggested a different mechanistic scenario when silanes are present in the reaction media. Isotopic-labeling experiments, kinetic isotope effects, and computational studies clearly reinforced this perception. Additionally, we also found that water has a deleterious effect by deactivating the Ni catalyst via formation of a new Ni-bridged hydroxo species that was characterized by X-ray crystallography. The order in each component was determined by plotting the initial rates of the C-OMe bond cleavage at varying concentrations. These data together with the in-situ-monitoring experiments by 1H NMR, EPR, IR spectroscopy, and theoretical calculations provided a mechanistic picture that involves Ni(I) as the key reaction intermediates, which are generated via comproportionation of initially formed Ni(II) species. This study strongly supports that a classical Ni(0)/Ni(II) for C-OMe bond cleavage is not operating, thus opening up new perspectives to be implemented in other related C-O bond-cleavage reactions.
- Cornella, Josep,Gómez-Bengoa, Enrique,Martin, Ruben
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supporting information
p. 1997 - 2009
(2013/04/10)
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- Tris(phosphane)-nickel(0)-ethene Complexes (dmpe)(PR3)Ni(C2H4). Molecular Structure of (dmpe)(PPh3)Ni(C2H4)
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Synthesis and properties of tris(phosphane)(ethene)nickel(0) complexes (dmpe)(PR3)Ni(C2H4) (R = CH3 (4), c-C6H11 (5), and C6H5 (6)) are reported.In solution, 4-6 are thermolabile and undergo ligand exchange reactions affording tetrakis(phosphane)nickel(0)
- Poerschke, Klaus R.,Mynott, Richard,Krueger, Carl,Romao, M. J.
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p. 1076 - 1081
(2007/10/02)
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- Preparation, x-ray molecular structure determination, and chemical properties of dinitrogen-coordinated cobalt complexes containing triphenylphosphine ligands and alkali metal or magnesium. Protonation of the coordinated dinitrogen to ammonia and hydrazine
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Treatment of CoH(N2)(PPh3)3 (1) with diethylmagnesium gave a magnesium-containing complex 2 formulated as [Co(N2)(PPh3)3]2Mg(THF)4 (THF = tetrahydrofuran). Subsequent reaction of 2 or direct reaction of 1 with LiBu afforded Li-containing complexes [Co(N2)(PPh3)3]Li(Et2O)3 (3) and [Co(N2)-(PPh3)3]Li(THF)3 (4) depending on the solvent employed. A Na-containing complex, [Co(N2)(PPh3)3]-Na(THF)3 (5), was also obtained by the reaction of 1 with sodium metal. The molecular structures of 3 and 4 were fully established by X-ray structural analysis. These complexes are isomorphous and have a threefold symmetry with the N2 ligand bridging Co and Li on its both ends with the N-N bond length of 1.167 (16) ? for 3 and 1.19 (4) ? for 4. In contrast to 1 whose coordinated N2 ligand is incapable of reacting with protic acids, the ligated N2 in the electron-rich cobalt complexes 2-5 is attacked by concentrated H2SO4 to afford hydrazine and ammonia. These complexes provide the first examples of the conversion of dinitrogen coordinated to cobalt into hydrazine and ammonia on hydrolysis. The corresponding iron analogue having a ligating dinitrogen also was prepared by the reaction of Fe(acac)3 with MgEt2 in the presence of 2-6 equiv of PPh3 under nitrogen. The complex was characterized as [FeEt(N2)-(PPh3)2]2Mg(THF) 4 (6). Complex 6 also affords hydrazine and ammonia on acidolysis.
- Yamamoto, Akio,Miura, Yoshikiyo,Ito, Takashi,Chen, Hui-Lin,Iri, Kiyoshi,Ozawa, Fumiyuki,Miki, Kunio,Sei, Tsuyoshi,Tanaka, Nobuo,Kasai, Nobutami
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p. 1429 - 1436
(2008/10/08)
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