Abstract The oxidation reactions of α-terpinene and 2,6-di-tert-butylphenol by vanadium(V) complexes were thoroughly examined using 1H NMR. The dioxovanadium(V) complex was more reactive than the corresponding oxo-peroxo vanadium(V) complex for the oxidation reaction of α-terpinene and 2,6-di-tert-butylphenol.
A detector and the output signal waveforms to be used for alignment in focused ion beam lithography are discussed. It is shown that a microchannelplate (MCP) is suitable for alignment signal detection. Alignment signals for 200-keV Si, 200-keV Be, and 100-keV Au ion beams are studied using the MCP. No deformation of alignment marks is observed in the case of light ions such as Si or Be. As a result, it is demonstrated that alignment can potentially be performed by detecting secondary electrons from the marks.
Reversibles Umschalten der Emissionsfarbe bei Photonenaufwärtskonversion durch Triplett-Triplett-Annihilierung weisen N. Yanai, N. Kimizuka et al. in ihrer Zuschrift auf S. 2856 nach. Ein Os-Komplex als Sensibilisator zeigt eine große Anti-Stokes-Verschiebung aufgrund einer direkten Singulett-nach-Triplett(S-T)-NIR-Anregung. In Kombination mit einem lumineszierenden Cyclophan als Emitter gelingt der thermisch reversible Farbwechsel zwischen grün leuchtendem kristallinem Zustand und gelb leuchtendem nematischem Zustand.
Abstract Reversibility in the formation reaction of a series of the oxo(peroxo)porphyrinatomolybdenums, [MoVIO(tmp)(O2)] 1, [MoVIO(tdcpp)(O2)] 2, [MoVIO(ttp)(O2)] 3, [MoVIO(tdmpp)(O2)] 4, and [MoVIO(tpp)(O2)] 5, was studied. In these dioxygen complexes with various porphyrin rings, two complexes, 2 and 4, were newly prepared by the solid-state reactions of corresponding Mo(IV) complexes with O2. All the complexes were characterized by IR, 1H NMR, and UV-vis spectroscopic measurements. In the reaction of O2 with [MoIVO(tdcpp)] 2r, which has bulky substituents with an electron-withdrawal character, the association rate constant was determined to be 1.2 × 10-2 dm3 mol-1 s-1 in toluene at 20 °C. The value of the rate constant is about one thirtieth of that for [MoIVO(tmp)] 1r, which also has bulky substituents. The result indicates that the electronic effects of the porphyrin rings, which reflect on the redox potentials of the central molybdenum ion, are important in determining kinetic and thermodynamic stability of the dioxygen complexes. All the dioxygen complexes undergo deoxygenation upon photoirradiation to give corresponding [MoIVO(por)]. The redioxygenation profiles of [MoIVO(por)] in the dark were also significantly affected by the steric bulkiness of the porphyrin ligands. While the bulky porphyrin complexes of 1 and 2 gave full recovery of the dioxygen complexes in the dark, less bulky porphyrin complexes of 3, 4, and 5 undergo some side reactions to Mo(V) species. The rate and extent of the Mo(V) complex formations increase with decreasing steric bulkiness.
Mononuclear oxovanadium(IV) and dioxovanadium(V) complexes of tris(2-pyridylmethyl)amine (tpa) have been prepared for the first time. Crystal structure determinations of three oxovanadium(IV) complexes, [VO(SO4)(tpa)], [VOCl(tpa)]PF6, or [VOBr(tpa)]PF6, and a dioxovanadium(V) complex [V(O)2(tpa)]PF6 disclosed that the tertiary nitrogen of the tpa ligand always occupies the trans-to-oxo site. The structures of an oxo-peroxo complex [VO(O2)(tpa)]Cl that was prepared previously and of a μ-oxo vanadium(III) complex [{VCl(tpa)}2(μ-O)](PF6)2 have also been determined. The tertiary nitrogen is located at a trans site to the peroxo and chloride ligands, respectively. The total sums of the four V–N bond lengths from the tpa ligand are remarkably similar among the six complexes, indicating that the vanadium oxidation states become less influential in tpa bonding due primarily to the coordination of electron-donating oxo ligand(s). Absorption spectra of [VOCl(tpa)]+ in acetonitrile showed a significant change upon addition of p-toluenesulfonic acid and HClO4, but not on addition of benzoic acid. Protonation at the oxo ligand by the former two acids is suggested. Cyclic voltammetric studies in acetonitrile verified the proton-coupled redox behavior of the VIII/VIV process involving the oxo ligand for the first time. From the dependence of the added p-toluenesulfonic acid to the CV, redox potentials for the following species have been estimated: [VIVOCl(tpa)]+/[VIIIOCl(tpa)] (E1/2 = −1.59 V vs. Fc+/Fc), [VIV(OH)Cl(tpa)]2+/[VIII(OH)Cl(tpa)]+ (Epc = −1.34 V), [VIV(OH2)Cl(tpa)]3+/[VIII(OH2)Cl(tpa)]2+ (Epa = −0.49 V), and [VIVCl2(tpa)]2+/[VIIICl2(tpa)]+ (E1/2 = −0.89 V). The reduction of [VV(O)2(tpa)]+ in 0.05 M [(n-Bu)4N]PF6 acetonitrile showed a major irreversible reduction wave V(V)/(IV) at −1.48 V. The metal reduction potentials of the oxovanadium(IV) and dioxovanadium(V) species are very close, reinforcing the significant influence of the oxo ligand(s).
A pair of seven-coordinate oxorhenium complexes of N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (tpen), [ReIVO(tpen)](ClO4)2 (1) and [ReVO(tpen)](ClO4)3 (2), and its R-1,2-propylenediamine an...
Abstract Tris(2-pyridylmethyl)amine (tpa) coordinates to oxorhenium(V) with two pyridyl and one amino nitrogen atoms leaving one 2-pyridylmethyl arm uncoordinated, giving a series of complexes, [Re(O)(L)(η3-tpa)]+ (L is chelating dianion), due to strong trans influence of the oxo ligand.
Abstract Substitution reactions of py-d5 for the terminal pyridines of the three triruthenium complexes, [Ru3(μ3-O)(μ-CH3COO)6(py)3]+ (1) (Ru3(III, III, III)), Ru3(μ3-O)(μ-CH3COO)6(py)3 (2) (Ru3(II, III, III)), and Ru3(μ3-O)(μ-CH3COO)6(CO)(py)2 (3) (Ru3(II, III, III)), have been studied in CD3CN by following the change in 1H NMR spectra. The rates are practically independent of [py-d5] (0.05–1.0 mol dm−3). The first-order rate constants are 3 × 10−5 s−1 at 55 °C (ΔH≠ = 123 ± 6 kJ mol−1, ΔS≠ = +41 ± 19 J K−1 mol−1), 5.9 × 10−4 s−1 at 50 °C (ΔH≠ = 122 ± 14 kJ mol−1, ΔS≠ = +69 ± 44 J K−1 mol−1), and 3 × 10−5 s−1 at 55 °C (ΔH≠ = 126 ± 9 kJ mol−1, ΔS≠ = +52 ± 27 J K−1 mol−1) for 1, 2, and 3, respectively. Rate constants appear to depend on the apparent oxidation state of the metal center. While the three Ru ions in 2 are equivalent and each ion has average oxidation number +2(2/3), Ru ions with coordinated py in 3 are in +3 oxidation state as the +2 oxidation state is localized at carbonyl-Ru ion. A dissociative mechanism is proposed for these reactions on the basis of the absence of [py-d5]-dependence, the activation parameters, and the comparison of the rate constants with those of the substitution of methanol-d4 for the terminal water ligands in [Ru3(μ3-O)(μ-CH3COO)6(H2O)3]+.
