Metallionen in einseitig von H-Brücken begrenzten Hohlräumen: ein Redoxpaar koordinativ ungesättigter paramagnetischer Co-OH-Komplexe

Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.

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Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands TpMe2,X (X=Me, H, Br) and TpiPr2

Hikichi

et al. 2001

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Hydrogen Bonds around M(μ‐O)₂M Rhombs: Stabilizing a {Co^III(μ‐O)₂Co^III} Complex at Room Temperature

et al. 2003

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cysteine-containing dipeptides in high yield and without significant loss of chirality at the C2-exomethine carbon atom. Finally, the application of this method to one-pot tandem dehydrocyclizations afforded a thiazole±thiazoline product in good overall yield and with excellent stereocontrol. Experimental SectionGeneral procedure for synthesis of thiazolines: Trifluoromethanesulfonic anhydride (50 mL, 0.3 mmol) was added slowly to a solution of triphenylphosphane oxide (167 mg, 0.6 mmol) in dry CH 2 Cl 2 (2 mL) at 0 8C. The reaction mixture was stirred for 10 min at 0 8C and then adjusted to the desired reaction temperature, followed by addition of the fully protected cysteine N-amide (0.2 mmol). The reaction progress was monitored by TLC. The reaction mixture was quenched with 10 % aqueous NaHCO 3 solution. The aqueous layer was extracted with CH 2 Cl 2 , and the combined organic layers were dried over Na 2 SO 4 , filtered, and concentrated. The resultant crude product was purified by flash chromatography with EtOAc/hexanes. More details and characterization data of the products can be found in the Supporting Information.

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Hydrogen Bonds around M(μ‐O)₂M Rhombs: Stabilizing a {Co^III(μ‐O)₂Co^III} Complex at Room Temperature

et al. 2003

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Metallionen in einseitig von H-Brücken begrenzten Hohlräumen: ein Redoxpaar koordinativ ungesättigter paramagnetischer Co-OH-Komplexe

Cited by 4 publications

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Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands TpMe2,X (X=Me, H, Br) and TpiPr2

Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands TpMe2,X (X=Me, H, Br) and TpiPr2

Hydrogen Bonds around M(μ‐O)₂M Rhombs: Stabilizing a {Co^III(μ‐O)₂Co^III} Complex at Room Temperature

Hydrogen Bonds around M(μ‐O)₂M Rhombs: Stabilizing a {Co^III(μ‐O)₂Co^III} Complex at Room Temperature

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Metallionen in einseitig von H-Brücken begrenzten Hohlräumen: ein Redoxpaar koordinativ ungesättigter paramagnetischer Co-OH-Komplexe

Cited by 4 publications

References 24 publications

Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands TpMe2,X (X=Me, H, Br) and TpiPr2

Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands TpMe2,X (X=Me, H, Br) and TpiPr2

Hydrogen Bonds around M(μ‐O)2M Rhombs: Stabilizing a {CoIII(μ‐O)2CoIII} Complex at Room Temperature

Hydrogen Bonds around M(μ‐O)2M Rhombs: Stabilizing a {CoIII(μ‐O)2CoIII} Complex at Room Temperature

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Hydrogen Bonds around M(μ‐O)₂M Rhombs: Stabilizing a {Co^III(μ‐O)₂Co^III} Complex at Room Temperature

Hydrogen Bonds around M(μ‐O)₂M Rhombs: Stabilizing a {Co^III(μ‐O)₂Co^III} Complex at Room Temperature