- Comparison of dppf-Supported Nickel Precatalysts for the Suzuki-Miyaura Reaction: The Observation and Activity of Nickel(I)
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Ni-based precatalysts for the Suzuki-Miyaura reaction have potential chemical and economic advantages compared to commonly used Pd systems. Here, we compare Ni precatalysts for the Suzuki-Miyaura reaction supported by the dppf ligand in 3 oxidation states, 0, I and II. Surprisingly, at 80 °C they give similar catalytic activity, with all systems generating significant amounts of NiI during the reaction. At room temperature a readily accessible bench-stable NiII precatalyst is highly active and can couple synthetically important heterocyclic substrates. Our work conclusively establishes that NiI species are relevant in reactions typically proposed to involve exclusively Ni0 and NiII complexes.
- Guard, Louise M.,Mohadjer Beromi, Megan,Brudvig, Gary W.,Hazari, Nilay,Vinyard, David J.
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- Anodic Mechanism of 1,1′-Bis(diphenylphosphino)ferrocenedicarbonylnickel Determined by Low-Temperature Spectroelectrochemistry
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[Ni(CO)2(dppf)] [1] {dppf = 1,1′-bis(diphenylphosphino)ferrocene} was made by reductive carbonylation of [NiCl2(dppf)] with [Fe(CO)5], similar to our recent report in Organometallics, 2019, 38, 586–592. Complex [1] showed two oxidation waves in the cyclic voltammogram. UV/Vis-NIR spectroelectrochemistry (SEC) and IR SEC at –30 °C as well as computational support by means of DFT was used to assign the oxidation state of both metal atoms after oxidation. The monocation [1]+ showed a strong NIR absorption band which was described as an IVCT [NiI→FeII] and inverse IVCT (iIVCT) or hole transfer [FeII→NiI] based on time dependence DFT (TD-DFT). The IR SEC spectrum of [1]+ showed multiple bands associated with two similar configurations, one which had the spin delocalized over both metal atoms and a second configuration where the spin is primarily Ni localized. The second oxidation to [1]2+ occurred at the Ni atom and resulted in release of a CO ligand followed by the formation of dimeric complex determined by low temperature IR SEC.
- Ringenberg, Mark R.,D?ttinger, Florian
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- Electronic Effect of Ligands on the Stability of Nickel-Ketene Complexes
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Electronically variant (dppf)Ni(ketene) complexes were synthesized and characterized to perform kinetic analysis on their decomposition through a decarbonylation/disproportion process to Ni-CO complexes and alkenes. Ligands containing electron-donating groups stabilized such complexes, whereas an electron-withdrawing group was found to destabilize them. Hammett analysis on the decomposition reaction revealed the buildup of negative charges in the rate-determining step, which corroborates past computational models.
- Al, Noman,Stolley, Ryan M.,Staudaher, Nicholas D.,Vanderlinden, Ryan T.,Louie, Janis
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p. 3750 - 3755
(2018/10/15)
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- Ferrocenyl phosphane nickel carbonyls: Synthesis, solid state structure, and their use as catalysts in the oligomerization of ethylene
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The synthesis of diverse ferrocenyl phosphane nickel carbonyls of type (FcPPh2)Ni(CO)3 (3), (FcPPh2)2Ni(CO)2 (4), fc(PR2Ni(CO)3)2 (R = Ph (6a), R = p-tolyl (6b)), and (fc(PPh2)2)Ni(CO)2 (7) (Fc = (η5-C5H5)(η5-C5H4)Fe, fc = (η5-C5H4)2Fe) starting from FcPPh2 (1), fc(PR2)2 (R = Ph (5a); R = p-tolyl (5b)), and Ni(CO)4 (2) is described. The structures of 3, 4, 6b, and 7 in the solid state are reported, intermolecular interactions by π-π-contacts are discussed. The behavior of 3, 4, 6a, 6b, and 7 towards the oligomerization of ethylene is reported. All compounds, except 4, were found to be inactive in homogeneous ethylene oligomerization, while they exhibit moderate activities (up to 660 kg prod/mol Ni h) in heterogeneous ethylene oligomerization experiments.
- Schaarschmidt, Dieter,Kühnert, Janett,Tripke, Sascha,Alt, Helmut G.,G?rl, Christian,Rüffer, Tobias,Ecorchard, Petra,Walfort, Bernhard,Lang, Heinrich
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p. 1541 - 1549
(2010/08/06)
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- Systematic variation of bidentate ligands used in aryl halide amination. Unexpected effects of steric, electronic, and geometric perturbations
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This paper presents effects of varying bidentate phosphine steric properties, electronic properties, and bite angle on product ratios in the amination of aryl bromides. Comparison of the ratios of amine products to dehydrohalogenation products showed that catalysts containing electron rich, modestly hindered phosphines with small bite angles (~-90°) gave the best selectivities. Surprisingly, the arene side product formed from reaction of alkylamines deuterated in the N-H position or deuterated in the position α to the nitrogen showed low levels of deuterium incorporation in many examples. Steric properties and ligand bite angle had the greatest impact on the selectivity for monoarylation versus diarylation of primary amines; ligands with small bite angles gave higher monoarylation-to-diarylation ratios, as did ligands with increased steric bulk. Electron poor or sterically hindered bidentate phosphines reduced the amount of product resulting from aryl exchange of electron rich palladium-bound arenes with those of aryl groups on the phosphine ligands.
- Hamann, Blake C.,Hartwig, John F.
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p. 3694 - 3703
(2007/10/03)
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