Model reactions for nitrogen fixation. Photo-induced formation and X-ray crystal structure of [Os2(NH3)8(MeCN)2(N2)]5+ from [Os VI (NH3)4N]3+

Che, Chi‐Ming; Lam, Michael; Tong, Wai-Fong; Lai, Ting-Fong; Lau, Tai‐Chu

doi:10.1039/c39890001883

Cited by 50 publications

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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 Figure 1. Spectral changes during the photolysis of [(NH 3 ) 5 Os II (m-N 2 )Os III (NH 3 ) 5 ](CF 3 SO 3 ) 5 (4.1 10 À4 m in 10 À3 m CF 3 SO 3 H) under argon at room temperature after irradiation for 0 (a), 30 (b), 60 (c), and 120 min (d) with l = 250-390 nm (UV filter Schott UG 11/2) in a 1 cm cell.…”

supporting

confidence: 61%

“…(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 À1 cm À1 ) and 238 nm (e = 41 000) with a shoulder at 260 nm (e = 21 000)) results in a bleaching of the green color owing to the disappearance of the 700 nm absorption (Figure 1).…”

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confidence: 99%

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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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confidence: 61%

mentioning

confidence: 99%

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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“…A classical evolution for metal-ni-trido functions is the coupling that forms N 2 and reduced metals. [63][64][65][66][67][68][69][70] Ruthenium nitrido derivatives are not exempt from that fate. [36,71] In fact, our computational studies indicate that N 2 formation from 1 a is exothermic by 34.5 kcal mol À1 .…”

Section: Synthesismentioning

confidence: 99%

Vicinal Dinitridoruthenium‐Substituted Polyoxometalates γ‐[XW₁₀O₃₈{RuN}₂]⁶⁻ (X=Si or Ge)

Besson

Musaev

Lahootun

et al. 2009

Chemistry A European J

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Reaction of the divacant polyoxometalate K(8)[gamma-XW(10)O(36)] (X = Si, Ge) with two equivalents of the metal-nitrido precursor Cs(2)[Ru(VI)NCl(5)], at room temperature in water, produces K(2)(Me(2)NH(2))(2)H(2)[gamma-XW(10)O(38){RuN}(2)], X = Si (DMA-1 a) or Ge (DMA-1 b). The X-ray crystal structures of both complexes show monomeric complexes with highly unusual vicinal terminal metal-nitrido units. The Ru[triple bond]N bond lengths are 1.594(10) and 1.612(11) A in 1 a and 1 b, respectively. EXAFS studies confirmed the key structural assignments from X-ray crystallography. The XANES spectrum of DMA-1 a, diamagnetism, NMR ((29)Si and (183)W) chemical shifts, voltammetric behavior, reductive titrations with [PW(12)O(40)](4-), and computational data are all consistent with d(2) Ru(VI) centers in these complexes. The FT-IR and Raman spectra show the expected vibrational modes of the {gamma-XW(10)} unit and the Ru[triple bond]N stretch at 1080 cm(-1), respectively. Interestingly, reduction of DMA-1 a by 4 equivalents of [PW(12)O(40)](4-) produces NH(3) in nearly quantitative yield. Cyclic voltammetry versus pH and calculations provide the energetics for the possible two-electron reduction and two-proton addition processes in this reaction.

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“…[5,6] In reverse,K unkely and Vogler observed photochemical N 2splitting of [(NH 3 ) 5 Os II (N 2 )Os III (NH 3 ) 5 ] 5+ (Scheme 1). [5,6] In reverse,K unkely and Vogler observed photochemical N 2splitting of [(NH 3 ) 5 Os II (N 2 )Os III (NH 3 ) 5 ] 5+ (Scheme 1).…”

mentioning

confidence: 99%

“…Osmium nitrides are involved in several model reactions relevant to N 2 -fixation, such as the interconversion of {Os VI N} and {Os II NH 3 }c omplexes by electron-proton transfer or the coupling of {Os V N} nitrides to N 2 -bridged dimers. [5,6] In reverse,K unkely and Vogler observed photochemical N 2splitting of [(NH 3 ) 5 Os II (N 2 )Os III (NH 3 ) 5 ] 5+ (Scheme 1). [7] [Os VI N(NH 3 ) 4 ] 3+ and [Os V N(NH 3 ) 4 ] 2+ were proposed as initial products presumably followed by disproportionation and hydrolysis of Os V to give NH 3 with atheoretical yield of 16 %.…”

mentioning

confidence: 99%

A Terminal Osmium(IV) Nitride: Ammonia Formation and Ambiphilic Reactivity

et al. 2016

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Low-valent osmium nitrides are discussed as intermediates in nitrogen fixation schemes.H owever,r ational synthetic routes that lead to isolable examples are currently unknown. Here,the synthesis of the square-planar osmium(IV) nitride [OsN(PNP)] (PNP = N(CH 2 CH 2 P(tBu) 2 ) 2 )isreported upon reversible deprotonation of osmium(VI) hydride [Os-(N)H(PNP)] + .T he Os IV complex shows ambiphilic nitride reactivity with SiMe 3 Br and PMe 3 ,r espectively.I mportantly, the hydrogenolysis with H 2 gives ammonia and the polyhydride complex [OsH 4 (HPNP)] in 80 %y ield. Hence,o ur results directly demonstrate the role of low-valent osmium nitrides and of heterolytic H 2 activation for ammonia synthesis with H 2 under basic conditions.

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Model reactions for nitrogen fixation. Photo-induced formation and X-ray crystal structure of [Os2(NH3)8(MeCN)2(N2)]5+ from [Os VI (NH3)4N]3+

Cited by 50 publications

References 0 publications

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

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

Vicinal Dinitridoruthenium‐Substituted Polyoxometalates γ‐[XW₁₀O₃₈{RuN}₂]⁶⁻ (X=Si or Ge)

A Terminal Osmium(IV) Nitride: Ammonia Formation and Ambiphilic Reactivity

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Model reactions for nitrogen fixation. Photo-induced formation and X-ray crystal structure of [Os2(NH3)8(MeCN)2(N2)]5+ from [Os VI (NH3)4N]3+

Cited by 50 publications

References 0 publications

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

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

Vicinal Dinitridoruthenium‐Substituted Polyoxometalates γ‐[XW10O38{RuN}2]6− (X=Si or Ge)

A Terminal Osmium(IV) Nitride: Ammonia Formation and Ambiphilic Reactivity

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

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

Vicinal Dinitridoruthenium‐Substituted Polyoxometalates γ‐[XW₁₀O₃₈{RuN}₂]⁶⁻ (X=Si or Ge)