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Weng Kee Leong - One of the best experts on this subject based on the ideXlab platform.
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isomers in the phosphine substituted Heteronuclear Cluster ruos3 µ h 2 co 12 pph3 a re examination
Inorganica Chimica Acta, 2021Co-Authors: Weng Kee LeongAbstract:Abstract The solution-state isomers of the Heteronuclear Cluster RuOs3(µ-H)2(CO)12(PPh3) have been re-examined in the light of conflicting structural assignments for a closely-related analogue. The result is a reassignment of the structures and hence the exchange processes observed in the NMR spectra.
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the aromatization of c5 rings on a Heteronuclear Cluster
European Journal of Inorganic Chemistry, 2007Co-Authors: Yong Leng Kelvin Tan, Weng Kee LeongAbstract:The reaction of the Heteronuclear Cluster RuOs3(μ-H)2(CO)13 with saturated and unsaturated C5 rings led to the aromatization of the rings to afford the Clusters RuOs3(μ-H)(CO)9(μ-CO)2(η5-C5R4R′). However, the reaction with cyclopentene gave the Cluster RuOs3(μ-H)3(CO)11(μ,η1:η2-C5H7) via C–H activation of an sp2 carbon instead. Thermolysis of two of the products, RuOs3(μ-H)(CO)9(μ-CO)2(η5-Cp′) and RuOs3(μ-H)(CO)9(μ-CO)2(η5-C5H4SiMe3), led to their isomerization to butterfly Clusters.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
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ditertiary phosphine derivatives of the Heteronuclear Cluster ruos3 μ h 2 co 13
Journal of Organometallic Chemistry, 2007Co-Authors: Yong Leng Kelvin Tan, Weng Kee LeongAbstract:Abstract The Heteronuclear Cluster RuOs 3 (μ-H) 2 (CO) 13 ( 1 ) reacted readily with a number of ditertiary phosphines under chemical activation with trimethylamine- N -oxide. The solid-state and solution structures of these derivatives have been examined. Six structural types have been characterized crystallographically, including one in which a phenyl group migrates from the ditertiary phosphine ligand to the metal framework. There are many more isomers present in solution, most of which are rapidly inter-converting via hydride migrations.
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the ditertiary phosphane bridged Heteronuclear Cluster ruos3 μ h 2 co 9 μ co 2 μ dppm synthesis and reactivity with alkynes
European Journal of Inorganic Chemistry, 2007Co-Authors: Yong Leng Kelvin Tan, Weng Kee LeongAbstract:A high-yielding alternative synthesis of the dppm-bridged Heteronuclear Cluster RuOs 3 (μ-H) 2 (CO) 9 (μ-CO) 2 (μ-dppm) (1) [dppm = bis(diphenylphosphanyl)methane] has been developed. Thermolysis of 1 resulted in dephenylation of both phosphane groups to afford the butterfly Cluster RuOs 3 -(CO) 12 (μ 4 ,κ 2 :κ 2 -PhPCH 2 PPh) (2). The reaction of 1 with selected alkynes afforded the products RuOs 3 (μ-H)(CO) 8 (μ-CO)(μ 3 ,κ 2 :κ 1 -PhPCH 2 PPh 2 )(μ 3 ,η 1 :η 2 :η 1 -L) (3) (L = alkyne) in which the alkyne is aligned parallel to an Os-Os bond (// Os-Os isomer). The Clusters incorporating internal alkynes underwent isomerization to the //Ru-Os isomer by alkyne and hydride migration. Several other Cluster products of these reactions were also identified, including RuOs 3 (μ-H)-(CO) 8 (μ-CO)(μ 3 ,κ 2 :κ 1 -PhPCH 2 PPh 2 )(μ 3 ,η 1 :η 2 :η 1 -tBuC 2 CHO) (6) in which the methyl group of the alkyne has been oxidized to an aldehyde.
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reactivity of the Heteronuclear Cluster ruos3 μ h 2 co 13 with indene
Journal of Organometallic Chemistry, 2007Co-Authors: Yong Leng Kelvin Tan, Weng Kee LeongAbstract:Abstract The Heteronuclear Cluster RuOs3(μ-H)2(CO)13 (1) reacts with indene under thermal activation to afford the novel Clusters RuOs3(μ-H)(CO)9(μ-CO)2(η5-C9H7) (3), RuOs3(μ-H)(CO)9(μ3,η5:η2:η2-C9H7) (4) and Ru2Os3(μ-H)(CO)11(μ3,η5:η2:η2-C9H7) (5), the latter two possessing indenyl ligands in the μ3,η5:η2:η2 bonding mode. Cluster 5 exists as a mixture of two isomers. The inter-relationship among the Clusters has also been investigated.
Helmut Schwarz - One of the best experts on this subject based on the ideXlab platform.
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electronic origin of the competitive mechanisms in the thermal activation of methane by the Heteronuclear Cluster oxide al2zno4
Angewandte Chemie, 2017Co-Authors: Shaodong Zhou, Maria Schlangen, Lei Yue, Helmut SchwarzAbstract:The thermal gas-phase reactions of [Al2ZnO4].+ with methane have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. Two competitive mechanisms, that is, hydrogen-atom transfer (HAT) and proton-coupled electron transfer (PCET) are operative. Interestingly, while the HAT process is influenced by the polarity of the transition structure, both the ionic nature of the metal–oxygen bond and the structural rigidity of the Cluster oxide affect the PCET pathway. As compared to the previously reported homonuclear [Al2O3].+ and [ZnO].+, the Heteronuclear oxide [Al2ZnO4].+ exhibits a much higher chemoselectivity towards methane. The electronic origins of the doping effect have been explored.
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electronic origins of the variable efficiency of room temperature methane activation by homo and Heteronuclear Cluster oxide cations xyo2 x y al si mg competition between proton coupled electron transfer and hydrogen atom transfer
Journal of the American Chemical Society, 2016Co-Authors: Jilai Li, Shaodong Zhou, Jun Zhang, Maria Schlangen, Thomas Weiske, Dandamudi Usharani, Sason Shaik, Helmut SchwarzAbstract:The reactivity of the homo- and Heteronuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) toward methane was studied using Fourier transform ion cyclotron resonance mass spectrometry, in conjunction with high-level quantum mechanical calculations. The most reactive Cluster by both experiment and theory is [Al2O2]•+. In its favorable pathway, this Cluster abstracts a hydrogen atom by means of proton-coupled electron transfer (PCET) instead of following the conventional hydrogen-atom transfer (HAT) route. This mechanistic choice originates in the strong Lewis acidity of the aluminum site of [Al2O2]•+, which cleaves the C–H bond heterolytically to form an Al–CH3 entity, while the proton is transferred to the bridging oxygen atom of the Cluster ion. In addition, a comparison of the reactivity of Heteronuclear and homonuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) reveals a striking doping effect by aluminum. Thus, the vacant s–p hybrid orbital on Al acts as an acceptor of the electron pair from methyl anio...
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Electronic Origins of the Variable Efficiency of Room-Temperature Methane Activation by Homo- and Heteronuclear Cluster Oxide Cations [XYO2]+ (X, Y = Al, Si, Mg): Competition between Proton-Coupled Electron Transfer and Hydrogen-Atom Transfer
2016Co-Authors: Shaodong Zhou, Jun Zhang, Maria Schlangen, Thomas Weiske, Dandamudi Usharani, Sason Shaik, Helmut SchwarzAbstract:The reactivity of the homo- and Heteronuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) toward methane was studied using Fourier transform ion cyclotron resonance mass spectrometry, in conjunction with high-level quantum mechanical calculations. The most reactive Cluster by both experiment and theory is [Al2O2]•+. In its favorable pathway, this Cluster abstracts a hydrogen atom by means of proton-coupled electron transfer (PCET) instead of following the conventional hydrogen-atom transfer (HAT) route. This mechanistic choice originates in the strong Lewis acidity of the aluminum site of [Al2O2]•+, which cleaves the C–H bond heterolytically to form an Al–CH3 entity, while the proton is transferred to the bridging oxygen atom of the Cluster ion. In addition, a comparison of the reactivity of Heteronuclear and homonuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) reveals a striking doping effect by aluminum. Thus, the vacant s–p hybrid orbital on Al acts as an acceptor of the electron pair from methyl anion (CH3–) and is therefore eminently important for bringing about thermal methane activation by PCET. For the Al-doped Cluster ions, the spin density at an oxygen atom, which is crucial for the HAT mechanism, acts here as a spectator during the course of the PCET mediated C–H bond cleavage. A diagnostic plot of the deformation energy vis-à-vis the barrier shows the different HAT/PCET reactivity map for the entire series. This is a strong connection to the recently discussed mechanism of oxidative coupling of methane on magnesium oxide surfaces proceeding through Grignard-type intermediates
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on the origin of the surprisingly sluggish redox reaction of the n2o co couple mediated by y2o2 and yalo2 Cluster ions in the gas phase
Angewandte Chemie, 2013Co-Authors: Zhechen Wang, Maria Schlangen, Helmut Schwarz, Shenggui HeAbstract:Catalytic conversion of harmful gases produced in fossil-fuel combustion or in large-scale chemical transformations, such as CO or the oxides of nitrogen into nitrogen and carbon dioxide, is of utmost importance both environmentally and economically. For example, N2O is a potent greenhouse gas with a warming potential exceeding that of CO2 by a factor of 300,1 and its role in the depletion of stratospheric ozone is well known.2 While these redox reactions are exothermic, for example ΔrH=−357 kJ mol−1 for the process N2O + CO→N2 + CO2, they do not occur directly to any measurable extent at either room or elevated temperatures because of high energy barriers that exceed the 193 kJ mol−1 for the N2O/CO couple. Catalysts are required to open-up new, energetically more favorable pathways,3 and the first example of a homogeneous catalysis in the gas phase, whereby atomic transition-metal cations bring about the efficient reduction of N2O by CO, was reported in a landmark study by Kappes and Staley,4 which was followed in the ensuing decades by numerous investigations.5 Recently, these studies addressed more specific questions, for example, “catalyst poisoning”, and these experiments revealed remarkable effects of both the Cluster size and the charge state of the catalysts.6 For example, the active species of the Pt7+ Cluster are Pt7+, [Pt7O]+, [Pt7O2]+, and [Pt7(CO)]+ and it has a turnover number >500 at room temperature. The adsorption of more than one CO molecule onto the Pt7+ Cluster, however, completely quenches the catalytic activity. Thus, coverage effects for any Cluster sizes can be studied at a strictly molecular level. Similarly, the concept of “single-site catalysts”,7 the proper characterization and identification of which constitutes one of the challenges and intellectual cornerstones in contemporary catalysis, can be probed directly in gas-phase experiments with mass-selected Heteronuclear metal-oxide Clusters. For example, catalytic room-temperature oxidation of CO by N2O can be mediated by the bimetallic oxide Cluster couple [AlVO4]+./[AlVO3]+..8 In the presence of CO, the Cluster ion [AlVO4]+. is efficiently reduced to [AlVO3]+., and if N2O is added, the reverse reaction occurs. Both processes are clean and proceed with efficiencies (ϕ) of 59 % and 65 %, respectively, relative to the collision rates. Most interestingly, the two redox reactions occur at the Al-Ot. unit of the Cluster (Ot: terminal oxygen atom); bond activation involving the V—O moiety cannot compete kinetically and thermochemically. Thus, the existence and operation of an “active site” of a catalyst can already be demonstrated in a rather small Heteronuclear Cluster.9
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probing elementary steps of nickel mediated bond activation in gas phase reactions ligand and Cluster size effects
Journal of Catalysis, 2011Co-Authors: Maria Schlangen, Helmut SchwarzAbstract:Abstract Mass-spectrometry-based experiments, complemented by computational studies, are presented which demonstrate the richness of nickel-containing reagents when employed in various bond-activation processes and conducted under single-collision conditions. We will address the chemistry of “naked” atomic Ni+, the dramatic effects of ligands L or of the size of Clusters, which they exhibit in thermal reactions of NiL+ or Ni n + (n = 2–30). Special emphasis will be paid to identify elementary steps and to uncover mechanistic principles; as an example, various aspects of the face-selective dehydrogenation of cyclohexane by homo- and Heteronuclear Cluster-ion dimers are discussed in some detail for the first time.
Ian D Salter - One of the best experts on this subject based on the ideXlab platform.
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the Heteronuclear Cluster chemistry of the group ib metals 19 x ray crystal structure and dynamic behaviour in solution of the mixed metal Cluster curu4 μ3 h 3 co 12 2 μ ph2p ch2 2pph2 an investigation of the effect of a bidentate diphosphine ligand linking two Cluster subunits
Polyhedron, 1996Co-Authors: Trushar Adatia, Ian D SalterAbstract:Abstract The structure of the mixed-metal Cluster [{CuRu 4 ( μ 3 -H) 3 (CO) 12 } 2 { μ -Ph 2 P(CH 2 ) 2 PPh 2 }] 1 has been determined by a single-crystal X-ray diffraction study, which shows that 1 is composed of two trigonal bipyramidal CuRu 4 subunits linked together by the bidentate diphosphine ligand Ph 2 P(CH 2 ) 2 PPh 2 . The copper atom in each CuRu 4 subunit occupies an axial site and each copper atom is bonded to a phosphorus atom at opposite ends of the Ph 2 P(CH 2 ) 2 PPh 2 ligand. A comparison of the equivalent metal-metal separations in the two subunits of 1 reveals that crystal packing forces cause differences of up to ca 0.118 A for the CuRu distances and up to ca 0.132 A for the RuRu separations. The structure of 1 is also compared with that of the closely related analogous Cluster [CuRu 4 ( μ 3 -H) 3 (CO) 12 (PMePh 2 )]. The 13 C{ 1 H} NMR spectrum of 1 at −90°C demonstrates that the whole of each {CuRu 4 ( μ 3 -H) 3 (CO) 12 } subunit undergoes rapid rotation around its CuP bond. The free energy of activation of this fluxional process seems surprisingly low in view of the fact that the CuRu 4 subunits are fairly sterically demanding.
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the Heteronuclear Cluster chemistry of the group ib metals 18 synthesis structural characterization and dynamic behaviour of the bimetallic hexanuclear group ib metal Cluster compounds m2ru4h2 μ dppf co 12 m cu ag or au dppf fe η5 c5h5pph2 2 x ray crystal structure of cu2ru4 μ3 h 2 μ dppf co 12
Polyhedron, 1995Co-Authors: Ian D Salter, Steven A Williams, Trushar AdatiaAbstract:Abstract Treatment of a dichloromethane solution of the salt [N(PPh3]2]2[Ru4(μ-H)2(CO)12] with two equivalents of the complex [M(NCMe)4]PF6 (M = Cu or Ag) at −30°C, followed by the addition of one equivalent of 1,1′-bis(diphenylphosphino)ferrocene (dppf) affords the mixed-metal Clusters [M2Ru49μ-H)2(μ-dppf)(CO)12] [M = Cu (1) or Ag (2)] in ca 45–60% yield. The analogous gold-containing species [Au12Ru4H2(μ-dppf)(CO)12] (3) was obtained in ca 70% yield by treating an acetone solution of [N(PPh3)2]2[Ru4(μ-H)2(CO)12] with a dichloromethane solution of the complex [Au2(μ-dppf)Cl2], in the presence of T1PF6. The novel Cluster compounds 1–3 have been characterized by IR and NMR spectroscopy and the structure of 1 has been determined by a single-crystal X-ray diffraction study. The metal core structure of 1 consists of a tetrahedron of ruthenium atoms capped by a copper atom, with one of the CuRu2 faces of the CuRu3 tetrahedron so formed further capped by a second copper atom to give a capped trigonal bipyramidal skeletal geometry. The other two CuRu2 faces of the CuRu3 tetrahedron are each capped by a triply bridging hydrido ligand, the bidentate diphosphine ligand bridges the two coinage metals and each ruthenium atom is bonded to three terminal CO groups. The spectroscopic data of the silver- and gold-containing species 2 and 3 are closely similar to those of 1, which suggests that 2 and 3 adopt similar metal core structures to that established for 1. However, the possibility that the capped trigonal bipyramidal metal framework of 3 is distorted by the dppf ligand towards a capped square-based pyramidal skeletal geometry cannot be excluded with the evidence available. Variable-temperature 1H and 31P{1H} NMR studies show that, at ambient temperatures in solution, the metal frameworks of all of the Clusters undergo dynamic behaviour involving coinage metal site exchange, even though the two Group IB metals are linked together by the bidentate diphosphine ligand dppf. Free energies of activation ( ΔG ‡ ) at the coalescence temperature of 47±1, 40±1 and ca 33 kJ mol−1 have been calculated for the skeletal rearrangements from the coalescence temperatures observed in the variable-temperature 31P{1H} NMR spectra of Clusters 1, 2 and 3, respectively. These values of ΔG ‡ are compared with those of structurally related analogous Clusters. In addition, the dppf ligand attached to the coinage metals in each of 1–3 is also stereochemically non-rigid in solution at room temperature and it undergoes a process involving inversion of configuration at the phosphorus atoms, together with twisting of the cyclopentadienyl rings. The skeletal rearrangement process and the fluxional behaviour of the dppf ligand are definitely independent for Clusters 2 and 3.
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the Heteronuclear Cluster chemistry of the group ib metals part xvii synthesis and x ray crystal structure of the hexanuclear mixed metal Cluster ag2ru4 μ3 h 2 co 12 p c6h4me 2 3 2 an investigation of the steric properties of the p c6h4me 2 3 ligand
Journal of Organometallic Chemistry, 1995Co-Authors: Paul J Mccarthy, Ian D Salter, Trushar AdatiaAbstract:Abstract Treatment of a dichloromethane solution of the salt [N(PPh 3 ) 2 ] 2 [Ru 4 (μ-H) 2 (CO) 12 ] with two equivalents of the complex [Ag(NCMe) 4 ]PF 6 at −30°C, followed by the addition of two equivalents of the very bulky phosphine ligand P(C 6 H 4 Me-2) 3 (cone angle 194°) affords the mixed-metal Cluster [Ag 2 Ru 4 (μ 3 -H) 2 (CO) 12 {P(C 6 H 4 Me-2) 3 } 2 ] ( I ) in ca. 70% yield. A single-crystal X-ray diffraction study has revealed that I has a capped trigonal bipyramidal metal framework structure, with the two silver atoms in close contact [Ag Ag 2.876(2)A]. This skeletal geometry is very surprising in view of a previous observation that P t Bu 3 (cone angle 182°), which is supposedly a less sterically demanding phosphine ligand than P(C 6 H 4 Me-2) 3 , is sufficiently bulky to prevent the two Ag(P t Bu 3 ) units being adjacent in the metal core of the closely related Cluster [Ag 2 Ru 4 (μ 3 -H) 2 (CO) 12 (P t Bu 3 ) 2 ]. In the solid-state structure of I , it appears that two of the three C 6 H 4 Me-2 rings in each of the two P(C 6 H 4 Me-2) 3 ligands can adopt relative orientations which allow the phosphine to behave as a less sterically demanding ligand than its large cone angle might otherwise suggest. Remarkably, the formal replacement of the two PPh 3 ligands attached to the silver atoms in the capped trigonal bipyramidal metal framework of the closely related Cluster [Ag 2 Ru 4 (μ 3 -H) 2 (CO) 12 (PPh 3 ) 2 ] by two P(C 6 H 4 Me-2) 3 groups in I causes very little change in most of the metal-metal distances, despite the fact that the cone angle of PPh 3 (145°) is 49° smaller than that of P(C 6 H 4 Me-2) 3 . In solution, compound I undergoes two types of dynamic behaviour at ambient temperatures. One process involves an intramolecular rearrangement of the metal core, which exchanges the two silver atoms between the two inequivalent sites, and the other process is an intermolecular exchange of P(C 6 H 4 Me-2) 3 ligands between Clusters.
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high resolution 31p 1h nuclear magnetic resonance studies of group ib metal Heteronuclear Cluster compounds in the solid state
Journal of Organometallic Chemistry, 1991Co-Authors: Scott S D Brown, Ian D Salter, Deborah J Smith, Nigel J Clayden, Christopher M DobsonAbstract:Abstract High-resolution 31 P-{ 1 H} NMR spectra of a series of crystalline mixed-metal Cluster compounds containing M(PR 3 ) (M = Cu, Ag, or Au; R = alkyl or aryl) fragments have been recorded using magic angle sample spinning. The solid-state spectra are compared with those measured for the same compounds in solution and the values of the chemical shifts and, for the silver-containing species, the magnitudes of J ( 107,109 AgP) av , are generally very similar. The solid-state NMR spectra suggest that the dynamic processes involving hydrido ligand site-exchange or intermolecular exchange of PR 3 ligands between Clusters, which have been previously observed at ambient temperature in solution for some of the Clusters studied, do not occur or are not sufficiently rapid to be detected when the same compounds are in the crystalline state. In addition, the intramolecular metal core rearrangements, which all of the bimetallic Clusters containing inequivalent M(PR 3 ) fragments undergo at ambient temperature in solution, are also not observed by solid-state NMR spectroscopy in the crystalline compounds. For some of the Clusters of this latter class, the solid-state spectra can provide useful structural information about the ground-state metal framework geometries which it is impossible to obtain from solution studies, even at low temperatures.
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the Heteronuclear Cluster chemistry of the group 1b metals part 15 effect of the nature of the group 1b metals and the cone angles of the attached phosphine ligands on the metal framework structures of Heteronuclear Cluster compounds synthesis structures and dynamic behaviour of the bimetallic hexanuclear Cluster compounds m2ru4h2 co 12 pr3 2 m cu r chme2 or c6h11 m ag or au r chme2 c6h11 or cme3
ChemInform, 1991Co-Authors: Carolyn J Brown, Paul J Mccarthy, Ian D SalterAbstract:Treatment of the salt [N(PPh3)2]2[Ru4(µ-H)2(CO)12] with 2 equivalents of the complex [M(NCMe)4]PF6 at –30 °C, followed by the addition of 2 equivalents of PR3, affords the hexanuclear Cluster compounds [M2Ru4(µ3-H)2(CO)12(PR3)2][M = Cu, R = CHMe2, or C6H11(C6H11= cyclohexyl); M = Ag, R = CHMe2, C6H11 or CMe3] in ca. 50–65% yield. The analogous gold-containing species [Au2Ru4H2(CO)12(PR3)2](R = CHMe2, C6H11, or CMe3) were prepared in ca. 30–50% yield from the reaction of [N(PPh3)2]2[Ru4(µ-H)2(CO)12] with 2 equivalents of the compound [AuCl(PR3)], in the presence of TIPF6. Despite the relatively large size of the P(C6H11)3 ligand, the Clusters [M2Ru4H2(CO)12{P(C6H11)3}2](M = Ag or Au) still adopt the capped trigonal-bipyramidal skeletal geometry, with the Group 1 B metals in close contact, which previous work has shown is preferred by Clusters of general formula [M2Ru4H2(CO)12L2](M = Cu, Ag, or Au) when L is a smaller monodentate phosphine or phosphite ligand. However, the smaller size of the copper atom relative to silver and gold means that the P(C6H11)3 ligand is too bulky to allow two adjacent Cu{P(C6H11)3} fragments to be accommodated in the metal framework of [Cu2Ru4(µ3-H)2-(CO)12{P(C6H11)3}2]. Thus, the Cluster is forced to adopt a sterically less-demanding skeletal geometry, which consists of a Ru4 tetrahedron with one edge bridged by a Cu{P(C6H11)3} unit and a non-adjacent face capped by the second such group. When the phosphine ligand P(CMe3)3, which is larger than P(C6H11)3, is attached to the Group 1 B metals in the Clusters [M2Ru4(µ3-H)2-(CO)12{P(CMe3)3}2](M = Ag or Au), the silver- and gold-containing species are also forced to adopt a similar sterically less-demanding edge-bridged trigonal-bipyramidal metal core structure. In addition, the P(CMe3)3 ligand seems to be too bulky to allow a hexanuclear Cluster of formula [Cu2Ru4H2(CO)12{P(CMe3)3}2] even to adopt an edge-bridged trigonal-bipyramidal metal framework structure and an attempt to prepare this species afforded the pentanuclear Cluster [CuRu4(µ3-H)3-(CO)12{P(CMe3)3}] instead. The phosphine ligand P(CHMe2)3, which is smaller than P(C6H11)3, is not sufficiently bulky to cause the metal cores of [M2Ru4(µ3-H)2(CO)12{P(CHMe2)3}2](M = Cu, Ag, or Au) to change from the preferred capped trigonal-bipyramidal skeletal geometry in the solid state, but a second isomer of the copper-containing Cluster, which probably has two face-capping Cu{P(CHMe2)3} units with no bonding interaction between them, is also present in solution at low temperatures. Variable-temperature 31P-{1H} and 1H n.m.r. spectroscopic studies demonstrate that the new Group 1 B metal Heteronuclear Cluster compounds undergo a variety of interesting dynamic processes in solution.
Maria Schlangen - One of the best experts on this subject based on the ideXlab platform.
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electronic origin of the competitive mechanisms in the thermal activation of methane by the Heteronuclear Cluster oxide al2zno4
Angewandte Chemie, 2017Co-Authors: Shaodong Zhou, Maria Schlangen, Lei Yue, Helmut SchwarzAbstract:The thermal gas-phase reactions of [Al2ZnO4].+ with methane have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. Two competitive mechanisms, that is, hydrogen-atom transfer (HAT) and proton-coupled electron transfer (PCET) are operative. Interestingly, while the HAT process is influenced by the polarity of the transition structure, both the ionic nature of the metal–oxygen bond and the structural rigidity of the Cluster oxide affect the PCET pathway. As compared to the previously reported homonuclear [Al2O3].+ and [ZnO].+, the Heteronuclear oxide [Al2ZnO4].+ exhibits a much higher chemoselectivity towards methane. The electronic origins of the doping effect have been explored.
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electronic origins of the variable efficiency of room temperature methane activation by homo and Heteronuclear Cluster oxide cations xyo2 x y al si mg competition between proton coupled electron transfer and hydrogen atom transfer
Journal of the American Chemical Society, 2016Co-Authors: Jilai Li, Shaodong Zhou, Jun Zhang, Maria Schlangen, Thomas Weiske, Dandamudi Usharani, Sason Shaik, Helmut SchwarzAbstract:The reactivity of the homo- and Heteronuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) toward methane was studied using Fourier transform ion cyclotron resonance mass spectrometry, in conjunction with high-level quantum mechanical calculations. The most reactive Cluster by both experiment and theory is [Al2O2]•+. In its favorable pathway, this Cluster abstracts a hydrogen atom by means of proton-coupled electron transfer (PCET) instead of following the conventional hydrogen-atom transfer (HAT) route. This mechanistic choice originates in the strong Lewis acidity of the aluminum site of [Al2O2]•+, which cleaves the C–H bond heterolytically to form an Al–CH3 entity, while the proton is transferred to the bridging oxygen atom of the Cluster ion. In addition, a comparison of the reactivity of Heteronuclear and homonuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) reveals a striking doping effect by aluminum. Thus, the vacant s–p hybrid orbital on Al acts as an acceptor of the electron pair from methyl anio...
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Electronic Origins of the Variable Efficiency of Room-Temperature Methane Activation by Homo- and Heteronuclear Cluster Oxide Cations [XYO2]+ (X, Y = Al, Si, Mg): Competition between Proton-Coupled Electron Transfer and Hydrogen-Atom Transfer
2016Co-Authors: Shaodong Zhou, Jun Zhang, Maria Schlangen, Thomas Weiske, Dandamudi Usharani, Sason Shaik, Helmut SchwarzAbstract:The reactivity of the homo- and Heteronuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) toward methane was studied using Fourier transform ion cyclotron resonance mass spectrometry, in conjunction with high-level quantum mechanical calculations. The most reactive Cluster by both experiment and theory is [Al2O2]•+. In its favorable pathway, this Cluster abstracts a hydrogen atom by means of proton-coupled electron transfer (PCET) instead of following the conventional hydrogen-atom transfer (HAT) route. This mechanistic choice originates in the strong Lewis acidity of the aluminum site of [Al2O2]•+, which cleaves the C–H bond heterolytically to form an Al–CH3 entity, while the proton is transferred to the bridging oxygen atom of the Cluster ion. In addition, a comparison of the reactivity of Heteronuclear and homonuclear oxide Clusters [XYO2]+ (X, Y = Al, Si, Mg) reveals a striking doping effect by aluminum. Thus, the vacant s–p hybrid orbital on Al acts as an acceptor of the electron pair from methyl anion (CH3–) and is therefore eminently important for bringing about thermal methane activation by PCET. For the Al-doped Cluster ions, the spin density at an oxygen atom, which is crucial for the HAT mechanism, acts here as a spectator during the course of the PCET mediated C–H bond cleavage. A diagnostic plot of the deformation energy vis-à-vis the barrier shows the different HAT/PCET reactivity map for the entire series. This is a strong connection to the recently discussed mechanism of oxidative coupling of methane on magnesium oxide surfaces proceeding through Grignard-type intermediates
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on the origin of the surprisingly sluggish redox reaction of the n2o co couple mediated by y2o2 and yalo2 Cluster ions in the gas phase
Angewandte Chemie, 2013Co-Authors: Zhechen Wang, Maria Schlangen, Helmut Schwarz, Shenggui HeAbstract:Catalytic conversion of harmful gases produced in fossil-fuel combustion or in large-scale chemical transformations, such as CO or the oxides of nitrogen into nitrogen and carbon dioxide, is of utmost importance both environmentally and economically. For example, N2O is a potent greenhouse gas with a warming potential exceeding that of CO2 by a factor of 300,1 and its role in the depletion of stratospheric ozone is well known.2 While these redox reactions are exothermic, for example ΔrH=−357 kJ mol−1 for the process N2O + CO→N2 + CO2, they do not occur directly to any measurable extent at either room or elevated temperatures because of high energy barriers that exceed the 193 kJ mol−1 for the N2O/CO couple. Catalysts are required to open-up new, energetically more favorable pathways,3 and the first example of a homogeneous catalysis in the gas phase, whereby atomic transition-metal cations bring about the efficient reduction of N2O by CO, was reported in a landmark study by Kappes and Staley,4 which was followed in the ensuing decades by numerous investigations.5 Recently, these studies addressed more specific questions, for example, “catalyst poisoning”, and these experiments revealed remarkable effects of both the Cluster size and the charge state of the catalysts.6 For example, the active species of the Pt7+ Cluster are Pt7+, [Pt7O]+, [Pt7O2]+, and [Pt7(CO)]+ and it has a turnover number >500 at room temperature. The adsorption of more than one CO molecule onto the Pt7+ Cluster, however, completely quenches the catalytic activity. Thus, coverage effects for any Cluster sizes can be studied at a strictly molecular level. Similarly, the concept of “single-site catalysts”,7 the proper characterization and identification of which constitutes one of the challenges and intellectual cornerstones in contemporary catalysis, can be probed directly in gas-phase experiments with mass-selected Heteronuclear metal-oxide Clusters. For example, catalytic room-temperature oxidation of CO by N2O can be mediated by the bimetallic oxide Cluster couple [AlVO4]+./[AlVO3]+..8 In the presence of CO, the Cluster ion [AlVO4]+. is efficiently reduced to [AlVO3]+., and if N2O is added, the reverse reaction occurs. Both processes are clean and proceed with efficiencies (ϕ) of 59 % and 65 %, respectively, relative to the collision rates. Most interestingly, the two redox reactions occur at the Al-Ot. unit of the Cluster (Ot: terminal oxygen atom); bond activation involving the V—O moiety cannot compete kinetically and thermochemically. Thus, the existence and operation of an “active site” of a catalyst can already be demonstrated in a rather small Heteronuclear Cluster.9
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probing elementary steps of nickel mediated bond activation in gas phase reactions ligand and Cluster size effects
Journal of Catalysis, 2011Co-Authors: Maria Schlangen, Helmut SchwarzAbstract:Abstract Mass-spectrometry-based experiments, complemented by computational studies, are presented which demonstrate the richness of nickel-containing reagents when employed in various bond-activation processes and conducted under single-collision conditions. We will address the chemistry of “naked” atomic Ni+, the dramatic effects of ligands L or of the size of Clusters, which they exhibit in thermal reactions of NiL+ or Ni n + (n = 2–30). Special emphasis will be paid to identify elementary steps and to uncover mechanistic principles; as an example, various aspects of the face-selective dehydrogenation of cyclohexane by homo- and Heteronuclear Cluster-ion dimers are discussed in some detail for the first time.
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the Heteronuclear Cluster chemistry of the group ib metals 19 x ray crystal structure and dynamic behaviour in solution of the mixed metal Cluster curu4 μ3 h 3 co 12 2 μ ph2p ch2 2pph2 an investigation of the effect of a bidentate diphosphine ligand linking two Cluster subunits
Polyhedron, 1996Co-Authors: Trushar Adatia, Ian D SalterAbstract:Abstract The structure of the mixed-metal Cluster [{CuRu 4 ( μ 3 -H) 3 (CO) 12 } 2 { μ -Ph 2 P(CH 2 ) 2 PPh 2 }] 1 has been determined by a single-crystal X-ray diffraction study, which shows that 1 is composed of two trigonal bipyramidal CuRu 4 subunits linked together by the bidentate diphosphine ligand Ph 2 P(CH 2 ) 2 PPh 2 . The copper atom in each CuRu 4 subunit occupies an axial site and each copper atom is bonded to a phosphorus atom at opposite ends of the Ph 2 P(CH 2 ) 2 PPh 2 ligand. A comparison of the equivalent metal-metal separations in the two subunits of 1 reveals that crystal packing forces cause differences of up to ca 0.118 A for the CuRu distances and up to ca 0.132 A for the RuRu separations. The structure of 1 is also compared with that of the closely related analogous Cluster [CuRu 4 ( μ 3 -H) 3 (CO) 12 (PMePh 2 )]. The 13 C{ 1 H} NMR spectrum of 1 at −90°C demonstrates that the whole of each {CuRu 4 ( μ 3 -H) 3 (CO) 12 } subunit undergoes rapid rotation around its CuP bond. The free energy of activation of this fluxional process seems surprisingly low in view of the fact that the CuRu 4 subunits are fairly sterically demanding.
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the Heteronuclear Cluster chemistry of the group ib metals 18 synthesis structural characterization and dynamic behaviour of the bimetallic hexanuclear group ib metal Cluster compounds m2ru4h2 μ dppf co 12 m cu ag or au dppf fe η5 c5h5pph2 2 x ray crystal structure of cu2ru4 μ3 h 2 μ dppf co 12
Polyhedron, 1995Co-Authors: Ian D Salter, Steven A Williams, Trushar AdatiaAbstract:Abstract Treatment of a dichloromethane solution of the salt [N(PPh3]2]2[Ru4(μ-H)2(CO)12] with two equivalents of the complex [M(NCMe)4]PF6 (M = Cu or Ag) at −30°C, followed by the addition of one equivalent of 1,1′-bis(diphenylphosphino)ferrocene (dppf) affords the mixed-metal Clusters [M2Ru49μ-H)2(μ-dppf)(CO)12] [M = Cu (1) or Ag (2)] in ca 45–60% yield. The analogous gold-containing species [Au12Ru4H2(μ-dppf)(CO)12] (3) was obtained in ca 70% yield by treating an acetone solution of [N(PPh3)2]2[Ru4(μ-H)2(CO)12] with a dichloromethane solution of the complex [Au2(μ-dppf)Cl2], in the presence of T1PF6. The novel Cluster compounds 1–3 have been characterized by IR and NMR spectroscopy and the structure of 1 has been determined by a single-crystal X-ray diffraction study. The metal core structure of 1 consists of a tetrahedron of ruthenium atoms capped by a copper atom, with one of the CuRu2 faces of the CuRu3 tetrahedron so formed further capped by a second copper atom to give a capped trigonal bipyramidal skeletal geometry. The other two CuRu2 faces of the CuRu3 tetrahedron are each capped by a triply bridging hydrido ligand, the bidentate diphosphine ligand bridges the two coinage metals and each ruthenium atom is bonded to three terminal CO groups. The spectroscopic data of the silver- and gold-containing species 2 and 3 are closely similar to those of 1, which suggests that 2 and 3 adopt similar metal core structures to that established for 1. However, the possibility that the capped trigonal bipyramidal metal framework of 3 is distorted by the dppf ligand towards a capped square-based pyramidal skeletal geometry cannot be excluded with the evidence available. Variable-temperature 1H and 31P{1H} NMR studies show that, at ambient temperatures in solution, the metal frameworks of all of the Clusters undergo dynamic behaviour involving coinage metal site exchange, even though the two Group IB metals are linked together by the bidentate diphosphine ligand dppf. Free energies of activation ( ΔG ‡ ) at the coalescence temperature of 47±1, 40±1 and ca 33 kJ mol−1 have been calculated for the skeletal rearrangements from the coalescence temperatures observed in the variable-temperature 31P{1H} NMR spectra of Clusters 1, 2 and 3, respectively. These values of ΔG ‡ are compared with those of structurally related analogous Clusters. In addition, the dppf ligand attached to the coinage metals in each of 1–3 is also stereochemically non-rigid in solution at room temperature and it undergoes a process involving inversion of configuration at the phosphorus atoms, together with twisting of the cyclopentadienyl rings. The skeletal rearrangement process and the fluxional behaviour of the dppf ligand are definitely independent for Clusters 2 and 3.
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the Heteronuclear Cluster chemistry of the group ib metals part xvii synthesis and x ray crystal structure of the hexanuclear mixed metal Cluster ag2ru4 μ3 h 2 co 12 p c6h4me 2 3 2 an investigation of the steric properties of the p c6h4me 2 3 ligand
Journal of Organometallic Chemistry, 1995Co-Authors: Paul J Mccarthy, Ian D Salter, Trushar AdatiaAbstract:Abstract Treatment of a dichloromethane solution of the salt [N(PPh 3 ) 2 ] 2 [Ru 4 (μ-H) 2 (CO) 12 ] with two equivalents of the complex [Ag(NCMe) 4 ]PF 6 at −30°C, followed by the addition of two equivalents of the very bulky phosphine ligand P(C 6 H 4 Me-2) 3 (cone angle 194°) affords the mixed-metal Cluster [Ag 2 Ru 4 (μ 3 -H) 2 (CO) 12 {P(C 6 H 4 Me-2) 3 } 2 ] ( I ) in ca. 70% yield. A single-crystal X-ray diffraction study has revealed that I has a capped trigonal bipyramidal metal framework structure, with the two silver atoms in close contact [Ag Ag 2.876(2)A]. This skeletal geometry is very surprising in view of a previous observation that P t Bu 3 (cone angle 182°), which is supposedly a less sterically demanding phosphine ligand than P(C 6 H 4 Me-2) 3 , is sufficiently bulky to prevent the two Ag(P t Bu 3 ) units being adjacent in the metal core of the closely related Cluster [Ag 2 Ru 4 (μ 3 -H) 2 (CO) 12 (P t Bu 3 ) 2 ]. In the solid-state structure of I , it appears that two of the three C 6 H 4 Me-2 rings in each of the two P(C 6 H 4 Me-2) 3 ligands can adopt relative orientations which allow the phosphine to behave as a less sterically demanding ligand than its large cone angle might otherwise suggest. Remarkably, the formal replacement of the two PPh 3 ligands attached to the silver atoms in the capped trigonal bipyramidal metal framework of the closely related Cluster [Ag 2 Ru 4 (μ 3 -H) 2 (CO) 12 (PPh 3 ) 2 ] by two P(C 6 H 4 Me-2) 3 groups in I causes very little change in most of the metal-metal distances, despite the fact that the cone angle of PPh 3 (145°) is 49° smaller than that of P(C 6 H 4 Me-2) 3 . In solution, compound I undergoes two types of dynamic behaviour at ambient temperatures. One process involves an intramolecular rearrangement of the metal core, which exchanges the two silver atoms between the two inequivalent sites, and the other process is an intermolecular exchange of P(C 6 H 4 Me-2) 3 ligands between Clusters.