Intrinsic Mechanisms of Oxidation Reactions as Revealed by Gas-Phase Experiments

Schröder, Detlef; Schwarz, Helmut

doi:10.1007/3418_056

Cited by 46 publications

(18 citation statements)

References 104 publications

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“…The former leads to methanol, and the latter is the first step in the oxidative coupling of methane to ethane. Therefore, the reactions of metal-oxide cations have received great attention and have been reviewed repeatedly (46)(47)(48). Here, we concentrate on a few key features that are of particular relevance for the activation of methane.…”

Section: Ligated Metal Cationsmentioning

confidence: 99%

Gas-phase activation of methane by ligated transition-metal cations

Schröder

Schwarz²

2008

Proc. Natl. Acad. Sci. U.S.A.

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Motivated by the search for ways of a more efficient usage of the large, unexploited resources of methane, recent progress in the gas-phase activation of methane by ligated transition-metal ions is discussed. Mass spectrometric experiments demonstrate that the ligands can crucially influence both reactivity and selectivity of transition-metal cations in bond-activation processes, and the most reactive species derive from combinations of transition metals with the electronegative elements fluorine, oxygen, and chlorine. Furthermore, the collected knowledge about intramolecular kinetic isotope effects associated with the activation of C-H(D) bonds of methane can be used to distinguish the nature of the bond activation as a mere hydrogen-abstraction, a metal-assisted mechanism or more complex reactions such as formation of insertion intermediates or -bond metathesis.bond activation ͉ kinetic isotope effects ͉ mass spectrometry

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Section: Ligated Metal Cationsmentioning

confidence: 99%

Gas-phase activation of methane by ligated transition-metal cations

Schröder

Schwarz²

2008

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

234

135

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“…The spectrum is measured ca. 5 min after mixing both components and shows the isotopolologues 1-d n (n = 0, 15,30,45,60). The broadening of the signals is explained further below.…”

Section: [Barmentioning

confidence: 92%

“…When fully deuterated [Au,Pt,(PPh 3 -d 15 ) 3 ] + (2-d 45 ) is employed for the CID experiment, the neutral loss corresponds to 84 mass units, thus indicating the formation of C 6 D 6 . Further experiments with the isotopologues [Au,Pt,(PPh 3 ) 2 , (PPh 3 -d 15 )] + (2-d 15 ) and [Au,Pt,(PPh 3 ),(PPh 3 -d 15 ) 2 ] + (2-d 30 ) result in the losses of C 6 H 6 , C 6 H 5 D, C 6 HD 5 , and C 6 D 6 as the only products (see Table 2 for the data as well as Figures S23− S26 for the corresponding spectra and breakdown curves).…”

Section: [Barmentioning

confidence: 99%

“…The signal is part of an ABCDE spin system, and the corresponding coupling constants are summarized in the Experimental Details. The presence of both a PPh 2 moiety and an ortho-metalated PPh 2 (o-C 6 15 in toluene is heated to 165°C in a closed vessel, phenyl-group exchange between the triphenylphosphine molecules occurs also in solution. This fact is illustrated by the mass spectrum of the resulting product mixture (Figure 11), in which [Au,(PPh 3 ) 2 ] +…”

Section: Reactivity In Solutionbenzene Eliminationmentioning

confidence: 99%

“…Note that the ratio of AuPt units and PPh 3 moieties in this F ] (see Figure S18). 15 , which was heated to 165°C in toluene in a closed vessel. The mixture was sprayed from methanol.…”

Section: Reactivity In Solutionbenzene Eliminationmentioning

confidence: 99%

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Phenyl-Group Exchange in Triphenylphosphine Mediated by Cationic Gold–Platinum Complexes—A Gas-Phase Mimetic Approach

2020

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The PPh 3 ligands in the heterodinuclear AuPt complex [(Ph 3 P)AuPt(PPh 3 ) 3 ][BAr 4 F ] (BAr 4 F = tetrakis[3,5bis(trifluoromethyl)phenyl]borate) exhibit a high fluxionality on the AuPt core. Fast intramolecular and slow intermolecular processes for the reversible exchange of the PPh 3 ligands have been identified. When [(Ph 3 P)AuPt(PPh 3 ) 3 ][BAr 4F ] is heated in solution, the formation of benzene is observed, and a trinuclear, cationic AuPt 2 complex is generated. This process is preceded by reversible phenyl-group exchange between the PPh 3 ligands present in the reaction mixture as elucidated by deuterium-labeling studies. Both the elimination of benzene and the preceding reversible phenyl-group exchange have originally been observed in massspectrometry-based CID experiments (CID = Collision-Induced Dissociation). While CID of mass-selected [Au,Pt,(PPh 3 ) 4 ] + results exclusively in the loss of PPh 3 , the resulting cation [Au,Pt,(PPh 3 ) 3 ] + selectively eliminates C 6 H 6 . Thus, the dissociation of a PPh 3 ligand from [Au,Pt,(PPh 3 ) 3 ] + is energetically not able to compete with processes which result in C−H-and C−P-bond cleavage. In both media, the heterobimetallic nature of the employed complexes is the key for the observed reactivity. Only the intimate interplay of the gas-phase investigations, studies in solution, and thorough DFT computations allowed for the elucidation of the mechanistic details of the reactivity of [(Ph 3 P)AuPt(PPh 3 ) 3 ][BAr 4 F ].

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Gas Phase Ligand Fragmentation to Unmask Reactive Metallic Species

O’Hair

2009

Reactive Intermediates

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The newer ionization methods of electrospray ionization, cold-spray ionization [1], atmospheric pressure chemical ionization [2], and matrix-assisted laser desorption [3] are making possible the mass spectrometry-based analysis of a diverse range of metal-based species [4]. With the very recent coupling of ESI to a glovebox [5], even challenging organometallic and inorganic species should be examinable via MS. Electrospray ionization has been particularly useful in the direct interception of reactive intermediates in solution. Pioneering work in the area includes that of Wilson and Canary in the early 1990s, who studied the intermediates formed in a number of textbook organic reactions including the Wittig, Mitsunobu, and Staudinger reactions [6] and CÀC bond-coupling reactions [7]. Since this topic has been recently reviewed [8,9] and also forms the basis of chapters 3, 4, 5 and 7 of this book, it is not discussed further here.The focus of this chapter is on the combined used of ESI and collision-induced dissociation (CID) as a means of synthesizing reactive intermediates so that their fundamental gas-phase reactivity may be examined via, for example, the use of ion-molecule reactions (IMR) [10] 1) . The motivation for such studies is to gain fundamental insights into metal-containing species that may have relevance to catalysis and metal-mediated reactions [13][14][15][16][17][18]. This field builds upon a wealth of previous metal ion chemistry studies in which other ionization techniques were utilized [14,[19][20][21][22][23][24][25][26][27][28]. Indeed, the potential for using CID to generate important (and sometimes novel) organic, organoelement and transition metal reactive intermediates was recognized some time ago. For example, Squires used decarboxylation of carboxylates and/or loss of aldehydes from alkoxide anions to study the gasphase chemistry of naked alkyl anions [29][30][31][32]. Thus, the prototypical methyl anion, 1) It is worth noting that photolysis [11] and thermolysis of metal complexes have a rich history and have been used as a route to reactive intermediates and new materials [12].

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Intrinsic Mechanisms of Oxidation Reactions as Revealed by Gas-Phase Experiments

Cited by 46 publications

References 104 publications

Gas-phase activation of methane by ligated transition-metal cations

Gas-phase activation of methane by ligated transition-metal cations

Phenyl-Group Exchange in Triphenylphosphine Mediated by Cationic Gold–Platinum Complexes—A Gas-Phase Mimetic Approach

Gas Phase Ligand Fragmentation to Unmask Reactive Metallic Species

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