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Solid‐State Thermolysis of a fac‐Rhenium(I) Carbonyl Complex with a Redox Non‐Innocent Pincer Ligand
Dr. Titel Jurca Dr. Wen‐Ching Chen Sheila Michel Dr. Ilia Korobkov Dr. Tiow‐Gan Ong Dr. Darrin S. Richeson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4278-4286
The development of rhenium(I) chemistry has been restricted by the limited structural and electronic variability of the common pseudo‐octahedral products fac‐[ReX(CO)3L2] (L2=α‐diimine). We address this constraint by first preparing the bidentate bis(imino)pyridine complexes [(2,6‐{2,6‐Me2C6H3N?CPh}2C5H3N)Re(CO)3X] (X=Cl 2 , Br 3 ), which were characterized by spectroscopic and X‐ray crystallographic means, and then converting these species into tridentate pincer ligand compounds, [(2,6‐{2,6‐Me2C6H3N?CPh}2C5H3N)Re(CO)2X] (X=Cl 4 , Br 5 ). This transformation was performed in the solid‐state by controlled heating of 2 or 3 above 200 °C in a tube furnace under a flow of nitrogen gas, giving excellent yields (≥95 %). Compounds 4 and 5 define a new coordination environment for rhenium(I) carbonyl chemistry where the metal center is supported by a planar, tridentate pincer‐coordinated bis(imino)pyridine ligand. The basic photophysical features of these compounds show significant elaboration in both number and intensity of the d–π* transitions observed in the UV/Vis spec tra relative to the bidentate starting materials, and these spectra were analyzed using time‐dependent DFT computations. The redox nature of the bis(imino)pyridine ligand in compounds 2 and 4 was examined by electrochemical analysis, which showed two ligand reduction events and demonstrated that the ligand reduction shifts to a more positive potential when going from bidentate 2 to tridentate 4 (+160 mV for the first reduction step and +90 mV for the second). These observations indicate an increase in electrostatic stabilization of the reduced ligand in the tridentate conformation. Elaboration on this synthetic methodology documented its generality through the preparation of the pseudo‐octahedral rhenium(I) triflate complex [(2,6‐{2,6‐Me2C6H3N?CPh}2C5H3N)Re(CO)2OTf] ( 7 , 93 % yield). 相似文献
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A Metal–Ligand Cooperative Pathway for Intermolecular Oxa‐Michael Additions to Unsaturated Nitriles
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Sébastien Perdriau Douwe S. Zijlstra Prof. Dr. Hero J. Heeres Prof. Dr. Johannes G. de Vries Dr. Edwin Otten 《Angewandte Chemie (International ed. in English)》2015,54(14):4236-4240
An unprecedented catalytic pathway for oxa‐Michael addition reactions of alcohols to unsaturated nitriles has been revealed using a PNN pincer ruthenium catalyst with a dearomatized pyridine backbone. The isolation of a catalytically competent Ru–dieneamido complex from the reaction between the Ru catalyst and pentenenitrile in combination with DFT calculations supports a mechanism in which activation of the nitrile through metal–ligand cooperativity is a key step. The nitrile‐derived Ru‐N moiety is sufficiently Brønsted basic to activate the alcohol and initiate conjugate addition of the alkoxide to the α,β‐unsaturated fragment. This reaction proceeds in a concerted manner and involves a six‐membered transition state. These features allow the reaction to proceed at ambient temperature in the absence of external base. 相似文献
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Microsecond X‐ray Absorption Spectroscopy Identification of CoI Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution
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Dr. Grigory Smolentsev Bianca Cecconi Alexander Guda Dr. Murielle Chavarot‐Kerlidou Prof. Jeroen A. van Bokhoven Dr. Maarten Nachtegaal Dr. Vincent Artero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15158-15162
Rational development of efficient photocatalytic systems for hydrogen production requires understanding the catalytic mechanism and detailed information about the structure of intermediates in the catalytic cycle. We demonstrate how time‐resolved X‐ray absorption spectroscopy in the microsecond time range can be used to identify such intermediates and to determine their local geometric structure. This method was used to obtain the solution structure of the CoI intermediate of cobaloxime, which is a non‐noble metal catalyst for solar hydrogen production from water. Distances between cobalt and the nearest ligands including two solvent molecules and displacement of the cobalt atom out of plane formed by the planar ligands have been determined. Combining in situ X‐ray absorption and UV/Vis data, we demonstrate how slight modification of the catalyst structure can lead to the formation of a catalytically inactive CoI state under similar conditions. Possible deactivation mechanisms are discussed. 相似文献
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Evidence of CuI/CuII Redox Process by X‐ray Absorption and EPR Spectroscopy: Direct Synthesis of Dihydrofurans from β‐Ketocarbonyl Derivatives and Olefins
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Hong Yi Zhixiong Liao Guanghui Zhang Guoting Zhang Chao Fan Xu Zhang Prof. Dr. Emilio E. Bunel Dr. Chih‐Wen Pao Prof. Dr. Jyh‐Fu Lee Prof. Dr. Aiwen Lei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):18925-18929
The CuI/CuII and CuI/CuIII catalytic cycles have been subject to intense debate in the field of copper‐catalyzed oxidative coupling reactions. A mechanistic study on the CuI/CuII redox process, by X‐ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopies, has elucidated the reduction mechanism of CuII to CuI by 1,3‐diketone and detailed investigation revealed that the halide ion is important for the reduction process. The oxidative nature of the thereby‐formed CuI has also been studied by XAS and EPR spectroscopy. This mechanistic information is applicable to the copper‐catalyzed oxidative cyclization of β‐ketocarbonyl derivatives to dihydrofurans. This protocol provides an ideal route to highly substituted dihydrofuran rings from easily available 1,3‐dicarbonyls and olefins. 相似文献
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Methandiide as a Non‐Innocent Ligand in Carbene Complexes: From the Electronic Structure to Bond Activation Reactions and Cooperative Catalysis
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Dipl.‐Chem. Julia Becker Tanja Modl Dr. Viktoria H. Gessner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(36):11295-11299
The synthesis of a ruthenium carbene complex based on a sulfonyl‐substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal–carbon interaction can be tuned between a Ru?C single bond with additional electrostatic interactions and a Ru?C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non‐polar bonds (O?H, H?H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non‐innocent ligand supporting the bond activation as nucleophilic center in the 1,2‐addition across the metal–carbon double bond. This metal–ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis. 相似文献
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Kinetics of Lifetime Changes in Bimetallic Nanocatalysts Revealed by Quick X‐ray Absorption Spectroscopy
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Dr. Matthias Filez Dr. Hilde Poelman Dr. Evgeniy A. Redekop Dr. Vladimir V. Galvita Dr. Konstantinos Alexopoulos Dr. Maria Meledina Dr. Ranjith K. Ramachandran Dr. Jolien Dendooven Prof. Christophe Detavernier Prof. Gustaaf Van Tendeloo Dr. Olga V. Safonova Dr. Maarten Nachtegaal Prof. Bert M. Weckhuysen Prof. Guy B. Marin 《Angewandte Chemie (International ed. in English)》2018,57(38):12430-12434
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Metal oxides are some of the most promising candidates as electrocatalysts for electrical‐energy‐storage (EES) systems. Particularly, perovskite and pyrochlore oxides have been intensively investigated as bifunctional electrocatalysts because of their superior catalytic activities during the oxygen‐reduction and ‐evolution reactions. However, the origin of the outstanding catalytic activities and structural changes of the materials are not clear, in part due to the difficulty in identification during electrocatalysis. In this Minireview, we present a critical overview of recent progress in understanding catalytic mechanisms of perovskite and pyrochlore oxides, highlighting the innovative in‐situ X‐ray absorption spectroscopy (XAS) analysis for electrochemical tests. 相似文献
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The structures formed during the photodicosiation of CBr4 in alcohol solution have been measured by means of a novel ultrafast time‐resolved x‐ray absorption fine structure (EXAFS) experimental system, suitable for the direct determination of ultrafast transient structures of molecules in the liquid and solid phase. The EXAFS spectra of the starting and final products of the reaction were measured and analyzed. 相似文献
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Anne Landwehr Dr. Balz Dudle Dr. Thomas Fox Dr. Olivier Blacque Prof. Dr. Heinz Berke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(18):5701-5714
The silyloxycyclopentadienyl hydride complexes [Re(H)(NO)(PR3)(C5H4OSiMe2tBu)] (R=iPr ( 3 a ), Cy ( 3 b )) were obtained by the reaction of [Re(H)(Br)(NO)(PR3)2] (R=iPr, Cy) with Li[C5H4OSiMe2tBu]. The ligand–metal bifunctional rhenium catalysts [Re(H)(NO)(PR3)(C5H4OH)] (R=iPr ( 5 a ), Cy ( 5 b )) were prepared from compounds 3 a and 3 b by silyl deprotection with TBAF and subsequent acidification of the intermediate salts [Re(H)(NO)(PR3)(C5H4O)][NBu4] (R=iPr ( 4 a ), Cy ( 4 b )) with NH4Br. In nonpolar solvents, compounds 5 a and 5 b formed an equilibrium with the isomerized trans‐dihydride cyclopentadienone species [Re(H)2(NO)(PR3)(C5H4O)] ( 6 a,b ). Deuterium‐labeling studies of compounds 5 a and 5 b with D2 and D2O showed H/D exchange at the HRe and HO positions. Compounds 5 a and 5 b were active catalysts in the transfer hydrogenation reactions of ketones and imines with 2‐propanol as both the solvent and H2 source. The mechanism of the transfer hydrogenation and isomerization reactions was supported by DFT calculations, which suggested a secondary‐coordination‐sphere mechanism for the transfer hydrogenation of ketones. 相似文献
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Mapping of the Photoinduced Electron Traps in TiO2 by Picosecond X‐ray Absorption Spectroscopy
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Dr. M. Hannelore Rittmann‐Frank Dr. Chris J. Milne Dr. Jochen Rittmann Dr. Marco Reinhard Dr. Thomas J. Penfold Prof. Majed Chergui 《Angewandte Chemie (International ed. in English)》2014,53(23):5858-5862
Titanium dioxide (TiO2) is the most popular material for applications in solar‐energy conversion and photocatalysis, both of which rely on the creation, transport, and trapping of charges (holes and electrons). The nature and lifetime of electron traps at room temperature have so far not been elucidated. Herein, we use picosecond X‐ray absorption spectroscopy at the Ti K‐edge and the Ru L3‐edge to address this issue for photoexcited bare and N719‐dye‐sensitized anatase and amorphous TiO2 nanoparticles. Our results show that 100 ps after photoexcitation, the electrons are trapped deep in the defect‐rich surface shell in the case of anatase TiO2, whereas they are inside the bulk in the case of amorphous TiO2. In the case of dye‐sensitized anatase or amorphous TiO2, the electrons are trapped at the outer surface. Only two traps were identified in all cases, with lifetimes in the range of nanoseconds to tens of nanoseconds. 相似文献
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Dr. Jay Agarwal Travis W. Shaw Charles J. Stanton III Prof. Dr. George F. Majetich Prof. Dr. Andrew B. Bocarsly Prof. Dr. Henry F. Schaefer III 《Angewandte Chemie (International ed. in English)》2014,53(20):5152-5155
The synthesis and characterization of the first catalytic manganese N‐heterocyclic carbene complexes are reported: MnBr(N‐methyl‐N′‐2‐pyridylbenzimidazol‐2‐ylidine)(CO)3 and MnBr(N‐methyl‐N′‐2‐pyridylimidazol‐2‐ylidine)(CO)3. Both new species mediate the reduction of CO2 to CO following two‐electron reduction of the MnI center, as observed with preparative scale electrolysis and verified with 13CO2. The two‐electron reduction of these species occurs at a single potential, rather than in two sequential steps separated by hundreds of millivolts, as is the case for previously reported MnBr(2,2′‐bipyridine)(CO)3. Catalytic current enhancement is observed at voltages similar to MnBr(2,2′‐bipyridine)(CO)3. 相似文献
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《Chemphyschem》2004,5(1):27-35
Detection of ultrafast transient structures and the evolution of ultrafast structural intermediates during the course of reactions has been a long standing goal of chemists and biologists. This article will be restricted to nanosecond, picosecond and shorter time‐resolved extended X‐ray absorption fine structure (EXAFS) studies, its aim being to present the progress and problems encounter in measurements and understanding the structure of transients. The recent advances in source technology has stimulated a wide variety of novel experiments using both synchrotrons and smaller laboratory size systems. With more efficient X‐ray lenses and detectors many of the previously difficult experiments to perform, because of the exposure time required and weak signals, will now be easily performed. The experimental system for the detection of ultrafast time‐resolved EXAFS spectra of molecules in liquids is described and the method for the analysis of EXAFS spectra to yield transient structures is given. We believe that utilizing our table‐top ultrafast X‐ray source and the polycapillary optics in conjunction with dispersive spectrometer and charge coupled devices (CCD) we will be able to determine the structure of many reaction intermediates and excited states of chemical and biological molecules in solid and liquid state. 相似文献
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Dr. Dipanwita Das Hemlata Agarwala Dr. Abhishek Dutta Chowdhury Tuhin Patra Dr. Shaikh M. Mobin Prof. Dr. Biprajit Sarkar Prof. Dr. Wolfgang Kaim Prof. Dr. Goutam Kumar Lahiri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7384-7394
The complex series [Ru(pap)(Q)2]n ([ 1 ]n–[ 4 ]n; n=+2, +1, 0, ?1, ?2) contains four redox non‐innocent entities: one ruthenium ion, 2‐phenylazopyridine (pap), and two o‐iminoquinone moieties, Q=3,5‐di‐tert‐butyl‐N‐aryl‐1,2‐benzoquinonemonoimine (aryl=C6H5 ( 1+ ); m‐(Cl)2C6H3 ( 2+ ); m‐(OCH3)2C6H3 ( 3+ ); m‐(tBu)2C6H3 ( 4 +)). A crystal structure determination of the representative compound, [ 1 ]ClO4, established the crystallization of the ctt‐isomeric form, that is, cis and trans with respect to the mutual orientations of O and N donors of two Q ligands, and the coordinating azo N atom trans to the O donor of Q. The sensitive C? O (average: 1.299(3) Å), C? N (average: 1.346(4) Å) and intra‐ring C? C (meta; average: 1.373(4) Å) bond lengths of the coordinated iminoquinone moieties in corroboration with the N?N length (1.292(3) Å) of pap in 1 + establish [RuIII(pap0)(Q.?)2]+ as the most appropriate electronic structural form. The coupling of three spins from one low‐spin ruthenium(III) (t2g5) and two Q.? radicals in 1 +– 4 + gives a ground state with one unpaired electron on Q.?, as evident from g=1.995 radical‐type EPR signals for 1 +– 4 +. Accordingly, the DFT‐calculated Mulliken spin densities of 1 + (1.152 for two Q, Ru: ?0.179, pap: 0.031) confirm Q‐based spin. Complex ions 1 +– 4 + exhibit two near‐IR absorption bands at about λ=2000 and 920 nm in addition to intense multiple transitions covering the visible to UV regions; compounds [ 1 ]ClO4–[ 4 ]ClO4 undergo one oxidation and three separate reduction processes within ±2.0 V versus SCE. The crystal structure of the neutral (one‐electron reduced) state ( 2 ) was determined to show metal‐based reduction and an EPR signal at g=1.996. The electronic transitions of the complexes 1 n– 4 n (n=+2, +1, 0, ?1, ?2) in the UV, visible, and NIR regions, as determined by using spectroelectrochemistry, have been analyzed by TD‐DFT calculations and reveal significant low‐energy absorbance (λmax>1000 nm) for cations, anions, and neutral forms. The experimental studies in combination with DFT calculations suggest the dominant valence configurations of 1 n– 4 n in the accessible redox states to be [RuIII(pap0)(Q.?)(Q0)]2+ ( 1 2+– 4 2+)→[RuIII(pap0)(Q.?)2]+ ( 1 +– 4 +)→[RuII(pap0)(Q.?)2] ( 1 – 4 )→[RuII(pap.?)(Q.?)2]? ( 1 ?– 4 ?)→[RuIII(pap.?)(Q2?)2]2? ( 1 2?– 4 2?). 相似文献
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Cobalt Complexes with Pyrazole Ligands as Catalyst Precursors for the Peroxidative Oxidation of Cyclohexane: X‐ray Absorption Spectroscopy Studies and Biological Applications
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Dr. Telma F. S. Silva Prof. Luísa M. D. R. S. Martins Prof. M. Fátima C. Guedes da Silva Dr. Maxim L. Kuznetsov Prof. Alexandra R. Fernandes Ana Silva Dr. Chun‐Jern Pan Dr. Jyh‐Fu Lee Prof. Bing‐Joe Hwang Prof. Armando J. L. Pombeiro 《化学:亚洲杂志》2014,9(4):1132-1143
[CoCl(μ‐Cl)(HpzPh)3]2 ( 1 ) and [CoCl2(HpzPh)4] ( 2 ) were obtained by reaction of CoCl2 with HC(pzPh)3 and HpzPh, respectively (HpzPh=3‐phenylpyrazole). The compounds were isolated as air‐stable solids and fully characterized by IR and far‐IR spectroscopy, MS(ESI+/?), elemental analysis, cyclic voltammetry (CV), controlled potential electrolysis, and single‐crystal X‐ray diffraction. Electrochemical studies showed that 1 and 2 undergo single‐electron irreversible CoII→CoIII oxidations and CoII→CoI reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex 1 , the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of 1 and 2 were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of 1 and 2 (that before structural relaxation) affects mostly the chloride and pyrazolyl ligands, whereas adiabatic oxidation (that after the geometry relaxation) and reduction are mostly metal centered. Compounds 1 and 2 and, for comparative purposes, other related scorpionate and pyrazole cobalt complexes, exhibit catalytic activity for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions (room temperature, aqueous H2O2). In situ X‐ray absorption spectroscopy studies indicated that the species derived from complexes 1 and 2 during the oxidation of cyclohexane (i.e., Ox‐ 1 and Ox‐ 2 , respectively) are analogous and contain a CoIII site. Complex 2 showed low in vitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines. 相似文献
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Amit Das Dipl.‐Chem. Thomas Michael Scherer Prasenjit Mondal Dr. Shaikh M. Mobin Prof. Dr. Wolfgang Kaim Prof. Dr. Goutam Kumar Lahiri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(45):14434-14443
New compounds [Ru(pap)2(L)](ClO4), [Ru(pap)(L)2], and [Ru(acac)2(L)] (pap=2‐phenylazopyridine, L?=9‐oxidophenalenone, acac?=2,4‐pentanedionate) have been prepared and studied regarding their electron‐transfer behavior, both experimentally and by using DFT calculations. [Ru(pap)2(L)](ClO4) and [Ru(acac)2(L)] were characterized by crystal‐structure analysis. Spectroelectrochemistry (EPR, UV/Vis/NIR), in conjunction with cyclic voltammetry, showed a wide range of about 2 V for the potential of the RuIII/II couple, which was in agreement with the very different characteristics of the strongly π‐accepting pap ligand and the σ‐donating acac? ligand. At the rather high potential of +1.35 V versus SCE, the oxidation of L? into L. could be deduced from the near‐IR absorption of [RuIII(pap)(L.)(L?)]2+. Other intense long‐wavelength transitions, including LMCT (L?→RuIII) and LL/CT (pap.?→L?) processes, were confirmed by TD‐DFT results. DFT calculations and EPR data for the paramagnetic intermediates allowed us to assess the spin densities, which revealed two cases with considerable contributions from L‐radical‐involving forms, that is, [RuIII(pap0)2(L?)]2+?[RuII(pap0)2(L.)]2+ and [RuIII(pap0)(L?)2]+?[RuII(pap0)(L?)(L?)]+. Calculations of electrogenerated complex [RuII(pap.?)(pap0)(L?)] displayed considerable negative spin density (?0.188) at the bridging metal. 相似文献
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Probing Long‐Lived Plasmonic‐Generated Charges in TiO2/Au by High‐Resolution X‐ray Absorption Spectroscopy
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Dr. Lucia Amidani Dr. Alberto Naldoni Dr. Marco Malvestuto Dr. Marcello Marelli Dr. Pieter Glatzel Dr. Vladimiro Dal Santo Prof. Federico Boscherini 《Angewandte Chemie (International ed. in English)》2015,54(18):5413-5416
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Michael R. Harpham Son C. Nguyen Zongrui Hou Jeffrey C. Grossman Charles B. Harris Michael W. Mara Andrew B. Stickrath Yosuke Kanai Alexie M. Kolpak Donghwa Lee Di‐Jia Liu Justin P. Lomont Kasper Moth‐Poulsen Nikolai Vinokurov Lin X. Chen K. Peter C. Vollhardt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(31):7812-7816