Prof. Dr. Kallol Ray

Profil

• Cluster/ NWG: Integrale Konzepte der Katalyse

  Quelle ↗

  Förderer: DFG Exzellenzinitiative Cluster Zeitraum: 11/2007 - 10/2012 Projektleitung: Prof. Dr. Kallol Ray

• Die Aufdeckung des photo-induzierten Assemblierungsmechanismus des lichtgetriebenen Wasseroxidationskomplexes in Photosystem II

  Quelle ↗

  Förderer: DFG Exzellenzinitiative Cluster Zeitraum: 11/2017 - 12/2018 Projektleitung: Prof. Dr. Athina Zouni

• Dioxygenase-Reaktivität von Hämoproteinen, die mit Nicht-Hem-Eisenkatalysatoren in asymmetrischen cis-Dihydroxylierungs- und Indol-Oxidationsreaktionen rekonstituiert wurden

  Quelle ↗

  Förderer: DFG Sachbeihilfe Internationale Kooperation Zeitraum: 06/2026 - 05/2029 Projektleitung: Prof. Dr. Kallol Ray

• EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  Quelle ↗

  Förderer: DFG Exzellenzstrategie Cluster Zeitraum: 01/2019 - 12/2025 Projektleitung: Prof. Dr. Arne Thomas

• EXC Katalyse (2): D1.2./E1, D3.4/E1

  Quelle ↗

  Förderer: DFG Exzellenzinitiative Cluster Zeitraum: 11/2012 - 10/2017 Projektleitung: Prof. Dr. Kallol Ray

• Forderung van Prof. Dr. Kallal Ray als Einstein-Profe

  Quelle ↗

  Förderer: Einstein Professur Zeitraum: 02/2026 - 07/2027 Projektleitung: Prof. Dr. Kallol Ray

• Heisenberg-Professur Ray

  Quelle ↗

  Förderer: DFG sonstige Programme Zeitraum: 05/2016 - 12/2017 Projektleitung: Prof. Dr. Kallol Ray

• Heisenberg-Professur Ray II

  Quelle ↗

  Förderer: DFG Heisenberg Programm Zeitraum: 01/2018 - 12/2019 Projektleitung: Prof. Dr. Kallol Ray

• Hoch-Valente Übergangsmetallreaktive Zwischenprodukte in Oxidationsreaktionen

  Quelle ↗

  Förderer: DAAD Zeitraum: 01/2019 - 06/2022 Projektleitung: Prof. Dr. Kallol Ray

• Multifunktionelle Katalyse durch Ni- und Fe- (Cyclam/ iso-Cyclam)-Komplexe

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 05/2018 - 07/2021 Projektleitung: Prof. Dr. Kallol Ray

• Untersuchung des kooperativen Effekts von zwei oder mehr Metallzentren in der metalloxido-vermittelten O-O Bindungsbildung und -spaltung

  Quelle ↗

  Förderer: DFG Sachbeihilfe Zeitraum: 07/2015 - 06/2018 Projektleitung: Prof. Dr. Kallol Ray

• VA: Final Scientific Workshop COST Action CM1305, Bildungszentrum Erkner e.V. (09.04.2018-11.04.2018)

  Quelle ↗

  Förderer: DFG sonstige Programme Zeitraum: 12/2017 - 05/2018 Projektleitung: Prof. Dr. Kallol Ray

• Science & Startups Berlin

  PT

  14 Treffer55.0%
  • Zuwendung im Rahmen des Programms „exist – Existenzgründungen aus der Wissenschaft“ aus dem Bundeshaushalt, Einzelplan 09, Kapitel 02, Titel 68607, Haushaltsjahr 2026, sowie aus Mitteln des Europäischen Strukturfonds (hier Euro-päischer Sozialfonds Plus – ESF Plus) Förderperiode 2021-2027 – Kofinanzierung für das Vorhaben: „exist Women“
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    55.0%

• Peugeot Citroen Automobiles S.A.

  PT

  140 Treffer54.8%
  • EU: Monomer Sequence Control in Polymers: Toward Next-Generation Precision Materials (EURO-SEQUENCES)
    P

    54.8%

• Ionera Technologies GmbH

  PT

  139 Treffer54.8%
  • EU: Monomer Sequence Control in Polymers: Toward Next-Generation Precision Materials (EURO-SEQUENCES)
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    54.8%

• Magwel NV

  PT

  88 Treffer54.2%
  • EU: Simulation in Multiscale Physical and Biological Systems (STIMULATE)
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    54.2%

• International Business Machines Corporation Research GmbH

  PT

  170 Treffer54.2%
  • EU: Simulation in Multiscale Physical and Biological Systems (STIMULATE)
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    54.2%
  • EU: Bottom-Up Generation of atomicalLy Precise syntheTIc 2D MATerials for High Performance in Energy and Electronic Applications – A Multi-Site Innovative Training Action (ULTIMATE)
    T

    51.9%

• NVIDIA GmbH

  PT

  88 Treffer54.2%
  • EU: Simulation in Multiscale Physical and Biological Systems (STIMULATE)
    P

    54.2%

• Spinverse

  P

  8 Treffer54.1%
  • EU: Stardust (STD)
    P

    54.1%

• Vlaams Instituut voor Biotechnologie

  P

  7 Treffer54.1%
  • EU: Stardust (STD)
    P

    54.1%

• BioModics ApS

  P

  7 Treffer54.1%
  • EU: Stardust (STD)
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    54.1%

• InnovationLab GmbH

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  91 Treffer53.0%
  • Interfaces in opto-electronic thin film multilayer devices
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    53.0%

• The biology and chemistry of high-valent iron–oxo and iron–nitrido complexes

  2012

  Nature Communications · 536 Zitationen · DOI

• Status of Reactive Non-Heme Metal–Oxygen Intermediates in Chemical and Enzymatic Reactions

  2014

  Journal of the American Chemical Society · 475 Zitationen · DOI

  Selective functionalization of unactivated C-H bonds, water oxidation, and dioxygen reduction are extremely important reactions in the context of finding energy carriers and conversion processes that are alternatives to the current fossil-based oil for energy. A range of metalloenzymes achieve these challenging tasks in biology by using cheap and abundant transition metals, such as iron, copper, and manganese. High-valent metal-oxo and metal-dioxygen (superoxo, peroxo, and hydroperoxo) cores act as active intermediates in many of these processes. The generation of well-described model compounds can provide vital insights into the mechanisms of such enzymatic reactions. This perspective provides a focused rather than comprehensive review of the recent advances in the chemistry of biomimetic high-valent metal-oxo and metal-dioxygen complexes, which can be related to our understanding of the biological systems.

• Axial ligand tuning of a nonheme iron(IV)–oxo unit for hydrogen atom abstraction

  2007

  Proceedings of the National Academy of Sciences · 407 Zitationen · DOI

  The reactivities of mononuclear nonheme iron(IV)-oxo complexes bearing different axial ligands, [Fe(IV)(O)(TMC)(X)](n+) [where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is NCCH(3) (1-NCCH(3)), CF(3)COO(-) (1-OOCCF(3)), or N(3)(-) (1-N(3))], and [Fe(IV)(O)(TMCS)](+) (1'-SR) (where TMCS is 1-mercaptoethyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane), have been investigated with respect to oxo-transfer to PPh(3) and hydrogen atom abstraction from phenol O H and alkylaromatic C H bonds. These reactivities were significantly affected by the identity of the axial ligands, but the reactivity trends differed markedly. In the oxidation of PPh(3), the reactivity order of 1-NCCH(3) > 1-OOCCF(3) > 1-N(3) > 1'-SR was observed, reflecting a decrease in the electrophilicity of iron(IV)-oxo unit upon replacement of CH(3)CN with an anionic axial ligand. Surprisingly, the reactivity order was inverted in the oxidation of alkylaromatic C H and phenol O H bonds, i.e., 1'-SR > 1-N(3) > 1-OOCCF(3) > 1-NCCH(3). Furthermore, a good correlation was observed between the reactivities of iron(IV)-oxo species in H atom abstraction reactions and their reduction potentials, E(p,c), with the most reactive 1'-SR complex exhibiting the lowest potential. In other words, the more electron-donating the axial ligand is, the more reactive the iron(IV)-oxo species becomes in H atom abstraction. Quantum mechanical calculations show that a two-state reactivity model applies to this series of complexes, in which a triplet ground state and a nearby quintet excited-state both contribute to the reactivity of the complexes. The inverted reactivity order in H atom abstraction can be rationalized by a decreased triplet-quintet gap with the more electron-donating axial ligand, which increases the contribution of the much more reactive quintet state and enhances the overall reactivity.

• Heme and Nonheme High-Valent Iron and Manganese Oxo Cores in Biological and Abiological Oxidation Reactions

  2018

  ACS Central Science · 384 Zitationen · DOI

  Utilization of O₂ as an abundant and environmentally benign oxidant is of great interest in the design of bioinspired synthetic catalytic oxidation systems. Metalloenzymes activate O₂ by employing earth-abundant metals and exhibit diverse reactivities in oxidation reactions, including epoxidation of olefins, functionalization of alkane C-H bonds, arene hydroxylation, and <i>syn</i>-dihydroxylation of arenes. Metal-oxo species are proposed as reactive intermediates in these reactions. A number of biomimetic metal-oxo complexes have been synthesized in recent years by activating O₂ or using artificial oxidants at iron and manganese centers supported on heme or nonheme-type ligand environments. Detailed reactivity studies together with spectroscopy and theory have helped us understand how the reactivities of these metal-oxygen intermediates are controlled by the electronic and steric properties of the metal centers. These studies have provided important insights into biological reactions, which have contributed to the design of biologically inspired oxidation catalysts containing earth-abundant metals like iron and manganese. In this Outlook article, we survey a few examples of these advances with particular emphasis in each case on the interplay of catalyst design and our understanding of metalloenzyme structure and function.

• Joint spectroscopic and theoretical investigations of transition metal complexes involving non-innocent ligands

  2007

  Dalton Transactions · 320 Zitationen · DOI

  A series of transition metal complexes involving non-innocent o-dithiolene and o-phenylenediamine ligands has been characterized in detail by various spectroscopic methods like magnetic circular dichroism (MCD), absorption (abs), resonance Raman (rR), electron paramagnetic resonance (EPR), and sulfur K-edge X-ray absorption spectroscopies. A computational model for the electronic structure of the complexes is then proposed based on the density functional theory (DFT) or ab-initio methods, which can successfully account for the observed trends in the experimental spectra (MCD, rR, and abs) of the complexes. Based on these studies, the innocent vs non-innocent nature of the ligands in a given transition metal complex is found to be dependent on the position of the central metal ion in the periodic table, its effective nuclear charge in interplay with relativistic effects.

• Iron and manganese oxo complexes, oxo wall and beyond

  2020

  Nature Reviews Chemistry · 300 Zitationen · DOI

• Oxidation Reactions with Bioinspired Mononuclear Non‐Heme Metal–Oxo Complexes

  2016

  Angewandte Chemie International Edition · 299 Zitationen · DOI

  The selective functionalization of strong C-H bonds and the oxidation of water by cheap and nontoxic metals are some of the key targets of chemical research today. It has been proposed that high-valent iron-, manganese-, and copper-oxo cores are involved as reactive intermediates in important oxidation reactions performed by biological systems, thus making them attractive targets for biomimetic synthetic studies. The generation and characterization of metal-oxo model complexes of iron, manganese, and copper together with detailed reactivity studies can help in understanding how the steric and electronic properties of the metal centers modulate the reactivity of the metalloenzymes. This Review provides a focused overview of the advances in the chemistry of biomimetic high-valent metal-oxo complexes from the last 5-10 years that can be related to our understanding of biological systems.

• Electronic Structure of Square Planar Bis(benzene-1,2-dithiolato)metal Complexes [M(L)₂]<i>^z</i> (<i>z</i> = 2−, 1−, 0; M = Ni, Pd, Pt, Cu, Au):  An Experimental, Density Functional, and Correlated ab Initio Study

  2005

  Inorganic Chemistry · 284 Zitationen · DOI

  The three diamagnetic square planar complexes of nickel(II), palladium(II), and platinum(II) containing two S,S-coordinated 3,5-di-tert-butylbenzene-1,2-dithiolate ligands, (L(Bu))(2-), namely [M(II)(L(Bu))(2)](2-), have been synthesized. The corresponding paramagnetic monoanions [M(II)(L(Bu))(L(Bu)(*))](-) (S = (1)/(2)) and the neutral diamagnetic species [M(II)(L(Bu)(*))(2)] (M = Ni, Pd, Pt) have also been generated in solution or in the solid state as [N(n-Bu)(4)][M(II)(L(Bu))(L(Bu)(*))] salts. The corresponding complex [Cu(III)(L(Bu))(2)](-) has also been investigated. The complexes have been studied by UV-vis, IR, and EPR spectroscopy and by X-ray crystallography; their electro- and magnetochemistry is reported. The electron-transfer series [M(L(Bu))(2)](2-,-,0) is shown to be ligand based involving formally one (L(Bu)(*))(-) pi radical in the monoanion or two in the neutral species [M(II)(L(Bu)(*))(2)] (M = Ni, Pd, Pt). Geometry optimizations using all-electron density functional theory with scalar relativistic corrections at the second-order Douglas-Kroll-Hess (DKH2) and zeroth-order regular approximation (ZORA) levels result in excellent agreement with the experimentally determined structures and electronic spectra. For the three neutral species a detailed analysis of the orbital structures reveals that the species may best be described as containing two strongly antiferromagnetically interacting ligand radicals. Furthermore, multiconfigurational ab initio calculations using the spectroscopy oriented configuration interaction (SORCI) approach including the ZORA correction were carried out. The calculations predict the position of the intervalence charge-transfer band well. Chemical trends in the diradical characters deduced from the multiconfigurational singlet ground-state wave function along a series of metals and ligands were discussed.

• Characterization of Porphyrin-Co(III)-‘Nitrene Radical’ Species Relevant in Catalytic Nitrene Transfer Reactions

  2015

  Journal of the American Chemical Society · 238 Zitationen · DOI

  To fully characterize the Co(III)-'nitrene radical' species that are proposed as intermediates in nitrene transfer reactions mediated by cobalt(II) porphyrins, different combinations of cobalt(II) complexes of porphyrins and nitrene transfer reagents were combined, and the generated species were studied using EPR, UV-vis, IR, VCD, UHR-ESI-MS, and XANES/XAFS measurements. Reactions of cobalt(II) porphyrins 1(P1) (P1 = meso-tetraphenylporphyrin (TPP)) and 1(P2) (P2 = 3,5-Di(t)Bu-ChenPhyrin) with organic azides 2(Ns) (NsN3), 2(Ts) (TsN3), and 2(Troc) (TrocN3) led to the formation of mono-nitrene species 3(P1)(Ns), 3(P2)(Ts), and 3(P2)(Troc), respectively, which are best described as [Co(III)(por)(NR″(•-))] nitrene radicals (imidyl radicals) resulting from single electron transfer from the cobalt(II) porphyrin to the 'nitrene' moiety (Ns: R″ = -SO2-p-C6H5NO2; Ts: R″ = -SO2C6H6; Troc: R″ = -C(O)OCH2CCl3). Remarkably, the reaction of 1(P1) with N-nosyl iminoiodane (PhI═NNs) 4(Ns) led to the formation of a bis-nitrene species 5(P1)(Ns). This species is best described as a triple-radical complex [(por(•-))Co(III)(NR″(•-))2] containing three ligand-centered unpaired electrons: two nitrene radicals (NR″(•-)) and one oxidized porphyrin radical (por(•-)). Thus, the formation of the second nitrene radical involves another intramolecular one-electron transfer to the "nitrene" moiety, but now from the porphyrin ring instead of the metal center. Interestingly, this bis-nitrene species is observed only on reacting 4(Ns) with 1(P1). Reaction of the more bulky 1(P2) with 4(Ns) results again in formation of mainly mono-nitrene species 3(P2)(Ns) according to EPR and ESI-MS spectroscopic studies. The mono- and bis-nitrene species were initially expected to be five- and six-coordinate species, respectively, but XANES data revealed that both mono- and bis-nitrene species are six-coordinate O(h) species. The nature of the sixth ligand bound to cobalt(III) in the mono-nitrene case remains elusive, but some plausible candidates are NH3, NH2(-), NsNH(-), and OH(-); NsNH(-) being the most plausible. Conversion of mono-nitrene species 3(P1)(Ns) into bis-nitrene species 5(P1)(Ns) upon reaction with 4(Ns) was demonstrated. Solutions containing 3(P1)(Ns) and 5(P1)(Ns) proved to be still active in catalytic aziridination of styrene, consistent with their proposed key involvement in nitrene transfer reactions mediated by cobalt(II) porphyrins.

• Molecular and Electronic Structure of Four‐ and Five‐Coordinate Cobalt Complexes Containing Two <i>o</i>‐Phenylenediamine‐ or Two <i>o</i>‐Aminophenol‐Type Ligands at Various Oxidation Levels: An Experimental, Density Functional, and Correlated ab initio Study

  2004

  Chemistry - A European Journal · 225 Zitationen · DOI

  The bidentate ligands N-phenyl-o-phenylenediamine, H(2)((2)L(N)IP), or its analogue 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, ((4)L(N)IP), react with [Co(II)(CH(3)CO(2))(2)]4H(2)O and triethylamine in acetonitrile in the presence of air yielding the square-planar, four-coordinate species [Co((2)L(N))(2)] (1) and [Co((4)L(O))(2)] (4) with an S=1/2 ground state. The corresponding nickel complexes [Ni((4)L(O))(2)] (8) and its cobaltocene reduced form [Co(III)(Cp)(2)][Ni((4)L(O))(2)] (9) have also been synthesized. The five-coordinate species [Co((2)L(N))(2)(tBu-py)] (2) (S=1/2) and its one-electron oxidized forms [Co((2)L(N))(2)(tBu-py)](O(2)CCH(3)) (2 a) or [Co((2)L(N))(2)I] (3) with diamagnetic ground states (S=0) have been prepared, as has the species [Co((4)L(O))(2)(CH(2)CN)] (7). The one-electron reduced form of 4, namely [Co(Cp)(2)][Co((4)L(O))(2)] (5) has been generated through the reduction of 4 with [Co(Cp)(2)]. Complexes 1, 2, 2 a, 3, 4, 5, 7, 8, and 9 have been characterized by X-ray crystallography (100 K). The ligands are non-innocent and may exist as catecholate-like dianions ((2)L(N)IP)(2-), ((4)L(N)IP)(2-) or pi-radical semiquinonate monoanions ((2)L(N)ISQ)(*) (-), ((4)L(N)ISQ)(*) (-) or as neutral benzoquinones ((2) L(N)IBQ)(0), ((4) L(N)IBQ)(0); the spectroscopic oxidation states of the central metal ions vary accordingly. Electronic absorption, magnetic circular dichroism, and EPR spectroscopy, as well as variable temperature magnetic susceptibility measurements have been used to experimentally determine the electronic structures of these complexes. Density functional theoretical (DFT) and correlated ab initio calculation have been performed on the neutral and monoanionic species [Co((1)L(N))(2)](0,-) in order to understand the structural and spectroscopic properties of complexes. It is shown that the corresponding nickel complexes 8 and 9 contain a low-spin nickel(II) ion regardless of the oxidation level of the ligand, whereas for the corresponding cobalt complexes the situation is more complicated. Spectroscopic oxidation states describing a d(6) (Co(III)) or d(7) (Co(II)) electron configuration cannot be unambiguously assigned.

• Description of the Ground‐State Covalencies of the Bis(dithiolato) Transition‐Metal Complexes from X‐ray Absorption Spectroscopy and Time‐Dependent Density‐Functional Calculations

  2007

  Chemistry - A European Journal · 221 Zitationen · DOI

  The electronic structures of [M(L(Bu))(2)](-) (L(Bu)=3,5-di-tert-butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(-) forms. The extent of electron transfer strongly depends on the effective nuclear charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(L(Bu))(2)](-) (M=Ni, Pd, Pt) and [Au(L(Bu))(2)] are best described as delocalized class III mixed-valence ligand radicals bound to low-spin d(8) central metal ions while [M(L(Bu))(2)](-) (M=Cu, Au) and [M(L(Bu))(2)](2-) (M=Ni, Pd, Pt) contain completely reduced dithiolato(2-) ligands. The case of [Co(L(Bu))(2)](-) remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S(1s)-->valence-pi versus S(1s)-->valence-sigma transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal-sulfur bonds from ligand K-edge absorption spectroscopy.

• Terminal Oxo and Imido Transition‐Metal Complexes of Groups 9–11

  2013

  European Journal of Inorganic Chemistry · 208 Zitationen · DOI

  Abstract This review summarizes the properties of group 9–11 metal–oxo and metal–imido complexes, which have been either isolated or proposed as reactive intermediates in metal‐catalyzed organic transformations. We begin with a general description of the bonding of transition‐metal–oxo and –imido complexes in various geometries, followed by a discussion of complexes from groups 9–11. The focus of this review is to provide a clear picture of the state of the art as well as insight towards potential future synthetic endeavors.

• Transition metal-mediated O–O bond formation and activation in chemistry and biology

  2021

  Chemical Society Reviews · 201 Zitationen · DOI

  O–O bond formation and activation reactions proceed <italic>via</italic> multi-step reactions in chemistry and biology and involve similar reactive intermediates like metal–oxo/oxyl, metal–superoxo, and/or metal–(hydro)peroxo species.

• Synthesis and reactivity of a mononuclear non-haem cobalt(IV)-oxo complex

  2017

  Nature Communications · 201 Zitationen · DOI

  Terminal cobalt(IV)-oxo (Co^IV-O) species have been implicated as key intermediates in various cobalt-mediated oxidation reactions. Herein we report the photocatalytic generation of a mononuclear non-haem [(13-TMC)Co^IV(O)]²⁺ (2) by irradiating [Co^II(13-TMC)(CF₃SO₃)]⁺ (1) in the presence of [Ru^II(bpy)₃]²⁺, Na₂S₂O₈, and water as an oxygen source. The intermediate 2 was also obtained by reacting 1 with an artificial oxidant (that is, iodosylbenzene) and characterized by various spectroscopic techniques. In particular, the resonance Raman spectrum of 2 reveals a diatomic Co-O vibration band at 770 cm^-1, which provides the conclusive evidence for the presence of a terminal Co-O bond. In reactivity studies, 2 was shown to be a competent oxidant in an intermetal oxygen atom transfer, C-H bond activation and olefin epoxidation reactions. The present results lend strong credence to the intermediacy of Co^IV-O species in cobalt-catalysed oxidation of organic substrates as well as in the catalytic oxidation of water that evolves molecular oxygen.

• The Electronic Structure of the Isoelectronic, Square-Planar Complexes [Fe^II(L)₂]²^-and [Co^III(L^Bu)₂]^-(L²^-and (L^Bu)²^-= Benzene-1,2-dithiolates):  An Experimental and Density Functional Theoretical Study

  2005

  Journal of the American Chemical Society · 187 Zitationen · DOI

  The electronic structures of two formally isoelectronic transition-metal dithiolato complexes [Fe(L)2]2- (1) and [Co(L Bu)2]1- (2) both possessing a spin triplet ground state (St=1) have been investigated by various spectroscopic and density functional methods; H2L Bu represents the pro-ligand 3,5-di-tert-butylbenzene-1,2-dithiol and H2L is the corresponding unsubstituted benzene-1,2-dithiol. An axial zero-field splitting (D) of +32 cm(-1) for 2 has been measured independently by SQUID magnetometry, far-infrared absorption, and variable-temperature and variable-field (VTVH) magnetic circular dichroism spectroscopies. A similar D value of +28 cm(-1) is obtained for 1 on the basis of VTVH SQUID measurements. The absorption spectra of 1 and 2 are found, however, to be very different. Complex 1 is light yellow in color with no intense transition in the visible region, whereas 2 is deep blue. DFT calculations establish that the electronic structures of the [Fe(L)2](2-) and [Co(L)2]1- anions are very different and explain the observed differences in their absorption spectra. On the basis of these spectroscopic and theoretical analyses, 1 is best described as containing an intermediate spin FeII ion, whereas for the corresponding cobalt complex, oxidation states describing a d6 (CoIII) or d7 (CoII) electron configuration cannot be unambiguously assigned. The physical origin of the large zero-field splitting in both 1 and 2 is found to be due to the presence of low-energy spin-conserved d-d excitations which lead to a large Dzz through efficient spin-orbit coupling. Differential covalency effects appear to be of limited importance for this property.

• Spectroscopic Capture and Reactivity of a Low‐Spin Cobalt(IV)‐Oxo Complex Stabilized by Binding Redox‐Inactive Metal Ions

  2014

  Angewandte Chemie International Edition · 183 Zitationen · DOI

  High-valent cobalt-oxo intermediates are proposed as reactive intermediates in a number of cobalt-complex-mediated oxidation reactions. Herein we report the spectroscopic capture of low-spin (S=1/2) Co(IV)-oxo species in the presence of redox-inactive metal ions, such as Sc(3+), Ce(3+), Y(3+), and Zn(2+), and the investigation of their reactivity in C-H bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis acidic metal ions to the cobalt-oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable [(TAML)Co(III)(O˙)](2-) species to a more stable [(TAML)Co(IV)(O)(M(n+))] core. The present report supports the proposed role of the redox-inactive metal ions in facilitating the formation of high-valent metal-oxo cores as a necessary step for oxygen evolution in chemistry and biology.

• Nonheme oxoiron(<scp>iv</scp>) complexes of pentadentate N5 ligands: spectroscopy, electrochemistry, and oxidative reactivity

  2012

  Chemical Science · 169 Zitationen · DOI

  Oxoiron(IV) species have been found to act as the oxidants in the catalytic cycles of several mononuclear nonheme iron enzymes that activate dioxygen. To gain insight into the factors that govern the oxidative reactivity of such complexes, a series of five synthetic S = 1 [Fe(IV)(O)(L(N5))](2+) complexes has been characterized with respect to their spectroscopic and electrochemical properties as well as their relative abilities to carry out oxo transfer and hydrogen atom abstraction. The Fe=O units in these five complexes are supported by neutral pentadentate ligands having a combination of pyridine and tertiary amine donors but with different ligand frameworks. Characterization of the five complexes by X-ray absorption spectroscopy reveals Fe=O bonds of ca. 1.65 Å in length that give rise to the intense 1s→3d pre-edge features indicative of iron centers with substantial deviation from centrosymmetry. Resonance Raman studies show that the five complexes exhibit ν(Fe=O) modes at 825-841 cm(-1). Spectropotentiometric experiments in acetonitrile with 0.1 M water reveal that the supporting pentadentate ligands modulate the E(1/2)(IV/III) redox potentials with values ranging from 0.83 to 1.23 V vs. Fc, providing the first electrochemical determination of the E(1/2)(IV/III) redox potentials for a series of oxoiron(IV) complexes. The 0.4-V difference in potential may arise from differences in the relative number of pyridine and tertiary amine donors on the L(N5) ligand and in the orientations of the pyridine donors relative to the Fe=O bond that are enforced by the ligand architecture. The rates of oxo-atom transfer (OAT) to thioanisole correlate linearly with the increase in the redox potentials, reflecting the relative electrophilicities of the oxoiron(IV) units. However this linear relationship does not extend to the rates of hydrogen-atom transfer (HAT) from 1,3-cyclohexadiene (CHD), 9,10-dihydroanthracene (DHA), and benzyl alcohol, suggesting that the HAT reactions are not governed by thermodynamics alone. This study represents the first investigation to compare the electrochemical and oxidative properties of a series of S = 1 Fe(IV)=O complexes with different ligand frameworks and sheds some light on the complexities of the reactivity of the oxoiron(IV) unit.

• Dioxygen activation chemistry by synthetic mononuclear nonheme iron, copper and chromium complexes

  2016

  Coordination Chemistry Reviews · 162 Zitationen · DOI

• An Oxocobalt(IV) Complex Stabilized by Lewis Acid Interactions with Scandium(III) Ions

  2010

  Angewandte Chemie International Edition · 160 Zitationen · DOI

  An elusive S=3/2 oxocobalt(IV) complex is stabilized by a Lewis acid interaction with a scandium(III) ion. The {CoIV-O-Sc}3+ unit, characterized by spectroscopic and DFT methods, is a stronger electron-transfer and H-atom abstraction agent but weaker oxo-transfer agent than the corresponding {FeIVO} complex (see scheme; L=tris[2-(N-tetramethylguanidyl)ethyl]amine). Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

• Lewis Acid Trapping of an Elusive Copper–Tosylnitrene Intermediate Using Scandium Triflate

  2012

  Journal of the American Chemical Society · 131 Zitationen · DOI

  High-valent copper-nitrene intermediates have long been proposed to play a role in copper-catalyzed aziridination and amination reactions. However, such intermediates have eluded detection for decades, preventing the unambiguous assignments of mechanisms. Moreover, the electronic structure of the proposed copper-nitrene intermediates has also been controversially discussed in the literature. These mechanistic questions and controversy have provided tremendous motivation to probe the accessibility and reactivity of Cu(III)-NR/Cu(II)N(•)R species. In this paper, we report a breakthrough in this field that was achieved by trapping a transient copper-tosylnitrene species, 3-Sc, in the presence of scandium triflate. The sufficient stability of 3-Sc at -90 °C enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as Cu(II)N(•)Ts (Ts = tosyl group) and not Cu(III)NTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting Cu(II)N(•)Ts cores as viable reactants in oxidation catalysis.

• Vibrational Markers for the Open-Shell Character of Transition Metal Bis-dithiolenes:  An Infrared, Resonance Raman, and Quantum Chemical Study

  2006

  Journal of the American Chemical Society · 110 Zitationen · DOI

  Transition metal complexes involving the benzene-1,2-dithiol (L(2-)) and Sellmann's 3,5-di-tert-butylbenzene-1,2-dithiol(L(Bu 2-)) ligands have been studied by UV-vis, infrared (IR), and resonance Raman (rR) spectroscopies. Raman spectra were obtained in resonance with the intervalence charge transfer (IVCT) bands in the near-infrared region and ligand-to-metal charge transfer (LMCT) bands in the near-UV region. Geometry optimization and frequency calculations using density functional theory (DFT) have been performed for [M(L)(2)](z) and [M(L(Bu))(2)](z) species (M = Ni, Pd, Pt, Co, Cu, Au, z = -1; M = Au, z = 0). On the basis of frequency calculations and normal-mode analysis, we have assigned the most important totally symmetric vibrations as well as corresponding overtone and combination bands that appear in rR spectra of compounds [Ni(L)(2)](1-), [M(L(Bu))(2)](1-) (M = Ni, Pt, Co, Cu). Experimental values of dimensionless normal coordinate displacements in excited states have been determined by fitting of rR spectra together with the absorption band shape, based on the time-dependent theory of Heller. Time-dependent density functional theory (TD-DFT) and multireference post-Hartree-Fock ab initio calculations, using the difference dedicated configuration interaction (MR-DDCI) method, were carried out to evaluate dimensionless normal coordinate displacements quantum chemically. The calculations show encouraging agreement with the experimental values. The large distortions along several normal modes led to significant vibronic broadening of IVCT and LMCT bands, and the broadening was accounted for in the deconvolution of the absorption spectra. The presence of an intense rR band around approximately 1100 cm(-1) was found to be a reliable marker for the presence of sulfur-based radicals.

• Redox-Noninnocence of the S,S‘-Coordinated Ligands in Bis(benzene-1,2-dithiolato)iron Complexes

  2005

  Journal of the American Chemical Society · 107 Zitationen · DOI

  The electronic structures of complexes of iron containing two S,S'-coordinated benzene-1,2-dithiolate, (L)(2)(-), or 3,5-di-tert-butyl-1,2-benzenedithiolate, (L(Bu))(2)(-), ligands have been elucidated in depth by electronic absorption, infrared, X-band EPR, and Mossbauer spectroscopies. It is conclusively shown that, in contrast to earlier reports, high-valent iron(IV) (d(4), S = 1) is not accessible in this chemistry. Instead, the S,S'-coordinated radical monoanions (L(*))(1)(-) and/or (L(Bu)(*))(1)(-) prevail. Thus, five-coordinate [Fe(L)(2)(PMe(3))] has an electronic structure which is best described as [Fe(III)(L)(L(*))(PMe(3))] where the observed triplet ground state of the molecule is attained via intramolecular, strong antiferromagnetic spin coupling between an intermediate spin ferric ion (S(Fe) = (3)/(2)) and a ligand radical (L(*))(1)(-) (S(rad) = (1)/(2)). The following complexes containing only benzene-1,2-dithiolate(2-) ligands have been synthesized, and their electronic structures have been studied in detail: [NH(C(2)H(5))(3)](2)[Fe(II)(L)(2)] (1), [N(n-Bu)(4)](2)[Fe(III)(2)(L)(4)] (2), [N(n-Bu)(4)](2)[Fe(III)(2)(L(Bu))(4)] (3); [P(CH(3))Ph(3)][Fe(III)(L)(2)(t-Bu-py)] (4) where t-Bu-py is 4-tert-butylpyridine. Complexes containing an Fe(III)(L(*))(L)- or Fe(III)(L(Bu))(L(Bu)(*))- moiety are [N(n-Bu)(4)][Fe(III)(2)(L(Bu))(3)(L(Bu)(*))] (3(ox)()), [Fe(III)(L)(L(*))(t-Bu-py)] (4(ox)()), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))] (7), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))(2)] (8), and [Fe(III)(L(Bu))(L(Bu)(*))(PPr(3))] (9), where Pr represents the n-propyl substituent. Complexes 2, 3(ox)(), 4, [Fe(III)(L)(L(*))(PMe(3))(2)] (6), and 9 have been structurally characterized by X-ray crystallography.

• Spectroscopic capture and reactivity of S = 1/2 nickel(iii)–oxygen intermediates in the reaction of a NiII-salt with mCPBA

  2012

  Chemical Communications · 95 Zitationen · DOI

  Ni(III)-intermediates are trapped by EPR and UV/Vis spectroscopy in the reaction of a Ni(II) salt with mCPBA. On the basis of their oxo-transfer and hydrogen-atom abstraction abilities the intermediates are assigned as the elusive terminal Ni(III)-oxo/hydroxo species. The findings suggest that Ni(III)-O(H) moieties are viable reactants in oxidation catalysis.

• Do S,S‘-Coordinated<i>o</i>-Dithiobenzosemiquinonate(1−) Radicals Exist in Coordination Compounds? The [Au^III(1,2-C₆H₄S₂)₂]¹^-^/0Couple

  2003

  Inorganic Chemistry · 94 Zitationen · DOI

  The square planar, light-green, diamagnetic complex [N(n-Bu)(4)][Au(III)(L(t)()(-)(Bu))(2)] (1) reacts with iodine in acetone affording the neutral paramagnetic species [Au(L(t)()(-)(Bu))(2)] (1a) (S = (1)/(2)) where H(2)[L(t)()(-)(Bu)] represents the ligand 3,5-di-tert-butyl-1,2-benzenedithiol. The corresponding complexes containing the unsubstituted ligand H(2)[L], 1,2-benzenedithiol, namely [N(n-Bu)(3)H][Au(L)(2)] (2) and [Au(L)(2)] (2a), have also been prepared and characterized by X-ray crystallography; the structure of the latter has been reported in ref 10. (197)Au Mössbauer spectra of 1 and 1a clearly show that the one-electron oxidation is ligand-centered and does not involve the formation of Au(IV) (d(7)). The spectroscopic features of the ligand mixed-valent species 1a were determined by UV-vis, EPR, and IR spectroscopy which allows the detection of S,S-coordinated 1,2-dithiobenzosemiquinonate(1-) radicals in coordination compounds.

• Reactivity of a Nickel(II) Bis(amidate) Complex with <i>meta</i>‐Chloroperbenzoic Acid: Formation of a Potent Oxidizing Species

  2015

  Chemistry - A European Journal · 93 Zitationen · DOI

  Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped following reaction of a Ni(II) precursor bearing a macrocyclic bis(amidate) ligand with meta-chloroperbenzoic acid (HmCPBA). This compound is only detectable at temperatures below 250 K and is much more reactive toward organic substrates (i.e., C-H bonds, C=C bonds, and sulfides) than previously reported well-defined nickel-oxygen species. Remarkably, this species is formed by heterolytic O-O bond cleavage of a Ni-HmCPBA precursor, which is concluded from experimental and computational data. On the basis of spectroscopy and DFT calculations, this reactive species is proposed to be a Ni(III) -oxyl compound.

• Charité – Universitätsmedizin Berlin

  EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  university

• Freie Universität Berlin

  EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  university

• Fritz-Haber-Institut der Max-Planck-Gesellschaft

  EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  other

• Helmholtz-Zentrum Berlin für Materialien und Energie

  EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  other

• Leibniz-Forschungsinstitut für Molekulare Pharmakologie

  EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  other

• Max-Planck-Institut für Kolloid- und Grenzflächenforschung

  EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  other

• Technische Universität Berlin

  Die Aufdeckung des photo-induzierten Assemblierungsmechanismus des lichtgetriebenen Wasseroxidationskomplexes in Photosystem II

  university

• Universität Potsdam

  EXC 2008: Unifying Systems in Catalysis (UniSysCat)

  university

Name

Prof. Dr. Kallol Ray

Titel

Prof. Dr.

Fakultät

Mathematisch-Naturwissenschaftliche Fakultät

Institut

Institut für Chemie

Arbeitsgruppe

Mechanismen und Spektroskopie Anorganischer Reaktionen (S)

Telefon

+49 30 2093-7385

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26.4.2026, 01:10:48