Characterization and reactions of osmium(IV) ammines

BUHR, J. D.; Winkler, Jay R.; Taube, Henry

doi:10.1021/ic50210a048

Cited by 53 publications

(33 citation statements)

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“…It is noteworthy that, in an early study, several Os(IV) ammine complexes were reported to give UVVis bands at lower energy positions with higher extinction coefficients as compared with the corresponding OsA C H T U N G T R E N N U N G (III) ammine complexes. [46] However, our result for the reference compound with Os in the + IV state in Figure 7 is not consistent with this early report. We speculate that this inconsistency might arise from the ammine ligands, which do not exist in our case.…”

Section: Characterization Of Os States For the Oxidationcontrasting

confidence: 99%

Osmium‐Catalyzed Selective Oxidations of Methane and Ethane with Hydrogen Peroxide in Aqueous Medium

et al. 2007

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Various transition metal chlorides including FeCl 3 , CoCl 2 , RuCl 3 , RhCl 3 , PdCl 2 , OsCl 3 , IrCl 3 , H 2 PtCl 6 , CuCl 2 and HAuCl 4 were studied for the selective oxidations of methane and ethane with hydrogen peroxide in aqueous medium. Among the metal chlorides investigated, osmiumA C H T U N G T R E N N U N G (III) chloride (OsCl 3 ) exhibited the highest turnover frequency (TOF) for the formation of organic oxygenates (mainly alcohols and aldehydes) from both methane and ethane. For the OsCl 3 -catalyzed oxidation of methane with hydrgen peroxide, methyl hydroperoxide was also formed together with methanol and formaldehyde. The effects of various kinetic factors on the catalytic behavior of the OsCl 3 -H 2 O 2 system were investigated, and TOF values of 12 and 41 h À1 could be obtained for oxygenate formation during the oxidations of methane and ethane, respectively. In the presence of OsCl 3 , NaClO, NaClO 4 or NaIO 4 as oxidant was incapable of oxidizing methane and ethane to the corresponding oxygenates, and the use of tert-butyl hydroperoxide (TBHP) instead of H 2 O 2 provided remarkably lower rates of formation of oxygenates. UV-Vis spectroscopic measurements suggested that OsCl 3 was probably oxidized into an Os(IV) species by H 2 O 2 in aqueous medium, and the Os(IV) species might be involved in the oxygenation of methane or ethane. The result that the conversions of both methane and ethane to oxygenates were suppressed by the addition of a radical scavenger suggested that the reactions proceeded via a radical pathway.

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Section: Characterization Of Os States For the Oxidationcontrasting

confidence: 99%

Osmium‐Catalyzed Selective Oxidations of Methane and Ethane with Hydrogen Peroxide in Aqueous Medium

et al. 2007

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“…The emission is attributed to the formation of [Os VI (NH 3 ) 4 N] 3+ (II). [7][8][9] This assignment is confirmed by the excitation spectrum of the photolyzed solution ( Figure 2) which closely resembles the absorption spectrum [7][8][9]12] (l max = 236 nm (3100 m À1 cm À1 ) with shoulders at 270 nm (1350), 325 nm (75), and 410 nm (e = 25 m À1 cm À1 )]) and the excitation spectrum of an authentic sample of II.…”

Section: Horst Kunkely and Arnd Vogler*supporting

confidence: 58%

Photolysis of Aqueous [(NH₃)₅Os(μ‐N₂)Os(NH₃)₅]⁵⁺: Cleavage of Dinitrogen by an Intramolecular Photoredox Reaction

Kunkely¹,

Vogler²

2010

Angew Chem Int Ed

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The lack of reactivity of dinitrogen which complicates its chemical conversion has been a challenge to chemists for many decades. [1,2] This difficulty is based on the extreme stability of the nitrogen-nitrogen triple bond. The huge energy difference between HOMO and LUMO (23 eV) makes N 2 rather redox inert. Moreover, the conversion of N 2 into simple species, such as ammonia or nitride, requires the transfer of six electrons. Such multi-electron transfer processes are generally associated with large activation barriers. Nevertheless, the reduction of N 2 to NH 3 occurs in nature through the utilization of the enzyme nitrogenase as catalyst. This conversion also takes place in the Haber-Bosch process, however, extreme conditions are required. Accordingly, it is of considerable interest to accomplish this reaction at ambient conditions. In principle, catalysis can be replaced by a photochemical procedure. The activation energy is then supplied by light. In favorable cases the photoactivation is selective and avoids interfering processes. Moreover, light may not only provide the activation energy but also the energy for an endothermic reaction which does not occur in catalysis at lower temperatures.In this context, it should be emphasized that some photochemical studies of binuclear N 2 -bridged complexes have been reported before. [3,4] However, in these cases N 2 is present in a reduced form containing a N À N double bond instead of a triple bond. This feature considerably facilitates the splitting of the N 2 ligand and may even take place thermally.[4] In contrast, the reductive splitting of the NÀN triple bond in a molecular complex is certainly much more difficult to achieve (see below), and has not yet been accomplished, neither thermally nor photochemically.Accordingly, we decided to examine a binuclear complex with a bridging N 2 ligand which largely preserves its integrity as a free dinitrogen molecule. This complex offers several attractive features. It is easily accessible and rather stable in aqueous solution in the absence of light. Owing to the intense color of I its disappearance can be precisely monitored. Although it is a mixed-valence system with considerable electronic delocalization between both metal centers, the triple bond of free N 2 is also present in the coordinated state as indicated by vibrational spectroscopy. Finally, the splitting of N 2 in the complex can be anticipated to proceed by a simple intramolecular redox reaction which produces only one excess electron that can lead to complications [Eq. (1)].The expected photoproduct [Os(NH 3 ) 4 N] 3+ is also quite stable and well characterized. [7][8][9] In this context, it should be stressed that the reverse reaction has been observed as photochemical [8,9] and thermal [10,11] process. It is clearly easy to couple two nitride complexes containing the Os VI N j moiety to give a binuclear N 2 complex owing to the extreme stability of the resulting NÀN triple bond.The irradiation of I (absorption spectrum: [5] l max = 700 nm (e = 4000 m ...

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“…Loss of dinitrogen from [Os(NH3)5N2] 2+ occurs on oxidation by Ce(IV), and opened a convenient route to [OsiNH^H^KClO^ (75), which in principle provides access to pentaammineosmium chemistry. But a violent explosion of fortunately a very small amount of this compound ended the use of ClOj as a counterion, to be replaced by CF3S03.…”

Section: Further Amplification Of Backbonding In Osmium Ammine Complexesmentioning

confidence: 99%

“…The compound [OsiNH^O.jSCFg)]-(03SCF3)2 was also prepared from [OsiNH^N^] 2 * as precursor, but with Br2 as oxidant in neat CF3SO3H medium (76). An exploration of some aspects of Os(IV) complexes with bis-and tris-halo ligands was carried out (75,77); Os(IV) is an oxidation state that is readily accessible when the complex is stabi lized by good σ-and π-donor ligands.…”

Section: Further Amplification Of Backbonding In Osmium Ammine Complexesmentioning

confidence: 99%

From Electron Transfer Reactions to the Effects of Backbonding

Taube

1997

Advances in Chemistry

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The initial motivation for extending the chemistry of ruthenium ammines was to provide new reagents for research on electron transfer reactions. Quite early in pursuing the preparative chemistry, an unexpected capac -ity of Ru(II) for backbonding was uncovered, and the systematic investi -gation of its influence on physical and chemical properties became a goal in its own right. The new directions led to the discovery of a num -ber of novel reactions, which in some cases led to novel products. The research has provided documentation of the effect of backbonding on ligand-to-metal charge transfer, ligand-metal distances, the intensities of infrared absorption by π-acceptor ligands, the acid-base properties of such ligands, the properties of co-ligands exerted by the electronic-with -drawing power of π-acceptor ligands, and on Ru(III)/Ru(II) redox potentials and enthalpies of complex formation. Some early results, which demonstrate the superior capacity of the osmium ammines to engage in backbonding, are also described. ONE OF THE THEMES OF MY EARLY RESEARCH at Stanford, begun late in1961, was the investigation of the mechanisms of substitution reactions of metal complexes by the application of isotope effects, mainly of oxygen. For example, we carried out kinetic and tracer studies in the alkaline hydrolysis of [Co(NH3)5(02CCF3)] 2+ (I) and attempted to generate intermediates such as might be implicated in SN1 mechanisms (e.g., we hoped to generate [Co(NH3)5] 3+ by the nitrosation of [CoiNH^N^P) (2). Mechanisms of Electron TransferThe major emphasis of the research in my group, however, was the investiga tion of the mechanisms of electron transfer reactions. In key experiments done

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Characterization and reactions of osmium(IV) ammines

Cited by 53 publications

References 1 publication

Osmium‐Catalyzed Selective Oxidations of Methane and Ethane with Hydrogen Peroxide in Aqueous Medium

Osmium‐Catalyzed Selective Oxidations of Methane and Ethane with Hydrogen Peroxide in Aqueous Medium

Photolysis of Aqueous [(NH₃)₅Os(μ‐N₂)Os(NH₃)₅]⁵⁺: Cleavage of Dinitrogen by an Intramolecular Photoredox Reaction

From Electron Transfer Reactions to the Effects of Backbonding

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Characterization and reactions of osmium(IV) ammines

Cited by 53 publications

References 1 publication

Osmium‐Catalyzed Selective Oxidations of Methane and Ethane with Hydrogen Peroxide in Aqueous Medium

Osmium‐Catalyzed Selective Oxidations of Methane and Ethane with Hydrogen Peroxide in Aqueous Medium

Photolysis of Aqueous [(NH3)5Os(μ‐N2)Os(NH3)5]5+: Cleavage of Dinitrogen by an Intramolecular Photoredox Reaction

From Electron Transfer Reactions to the Effects of Backbonding

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Photolysis of Aqueous [(NH₃)₅Os(μ‐N₂)Os(NH₃)₅]⁵⁺: Cleavage of Dinitrogen by an Intramolecular Photoredox Reaction