Silylation of Dinitrogen Catalyzed by Hydridodinitrogentris(Triphenylphosphine)Cobalt(I)

Recently, homogeneous cobalt systems were reported to catalyze the reductive silylation of dinitrogen. In this study the investigations on the silylation of dinitrogen catalyzed by CoH(PPh3)3N2 are presented. We show that in the presence of the title compound, the reaction of N2 with trimethylsilylchloride and sodium yields, on average, 6.7 equivalents of tris(trimethylsilyl)amine per Co atom in THF (tetrahydrofuran). The aim was to elucidate whether the active catalyst is: (a) the [Co(PPh3)3N2]− anion formed after two-electron reduction of the title compound; or (b) a species formed via decomposition of CoH(PPh3)3N2 in the presence of the highly reactive substrates. Time profile, and IR and EPR spectroscopic investigations show instability of the pre-catalyst under the applied conditions which suggests that the catalytically active species is formed through in situ modification of the pre-catalyst

Decarboxylative Etherification of Aromatic Carboxylic Acids

Decarboxylative Chan–Evans–Lam-type couplings are presented as a new strategy for the regiospecific construction of diaryl and alkyl aryl ethers starting from easily available aromatic carboxylic acids. They allow converting various aromatic carboxylate salts into the corresponding aryl ethers by reaction with alkyl orthosilicates or aryl borates, under aerobic conditions in the presence of silver carbonate as the decarboxylation catalyst and copper acetate as the cross-coupling catalyst

Reaction progress kinetic analysis as tool to reveal ligand effects in Ce(IV)-driven IrCp* catalyzed water oxidation

A series of iridium-based complexes have been evaluated in Ce(IV)-driven water oxidation catalysis. Detailed kinetic data have been obtained from UV–vis stopped-flow experiments, and these data have been analyzed using reaction progress kinetic analysis. The graphical plots show that there are three clear phases in the reaction: catalyst activation, water oxidation catalysis, and cerium concentration controlled catalysis at the end of the reaction. The ligand attached to the IrCp* complex has a clear influence on both the activation as well as the catalysis. Some bidentate ligands result in relatively slow catalysis, and the first-order in iridium supports the presence of mononuclear active species; however, other bidentates form the more active dinuclear species. Monodentate ligands allow the formation of bis-μ-oxo bridged dimeric species, supported by kinetics displaying 1.6-order in [Ir], leading to high reaction rates

Binuclear [(cod)(Cl)Ir(bpi)Ir(cod)]+ for Catalytic Water Oxidation

The binuclear iridium complex [(cod)(Cl)Ir(bpi)Ir(cod)]PF6 (bpi = (pyridin-2-ylmethyl)(pyridin-2-ylmethylene)amine; cod = 1,5-cyclooctadiene) reveals a noteworthy asymmetric binuclear coordination geometry, wherein the bpi ligand acts as a heteroditopic ligand and has an unusual π-coordinated imine moiety. This species is an effective precatalyst for water oxidation. After a short incubation time the catalyst reveals a turnover frequency of 3400 mol mol-1 s-1 with an overall turnover number >1000. © 2011 American Chemical Society.Financial support from the European Research Council (ERC Grant Agreement 202886-CatCIR), NWO-CW (VIDI grant 700.55.426, VENI grant 700.59.410), the MEC/FEDER (Project CTQ2008-03860, Spain), and the University of Amsterdam is gratefully acknowledged.Peer Reviewe

Photo- and Thermal Isomerization of (TP)Fe(CO)Cl₂ [TP = Bis(2-diphenylphosphinophenyl)­phenylphosphine]

The title complex displayed structural flexibility via photo- and thermal-isomerization reactions between three isomers: (<i>mer</i>-TP)­Fe­(CO)­Cl₂ (<b>A</b>), <i>unsym</i>-(<i>fac</i>-TP)­Fe­(CO)­Cl₂ (<b>B</b>), and <i>sym</i>-(<i>fac-</i>TP)­Fe­(CO)­Cl₂ (<b>C</b>). Irradiation of <b>A</b> at RT with 525 nm light selectively produces <b>B</b>, while at 0 °C isomer <b>C</b> is formed with the intermediacy of <b>B</b>. UV–vis spectroscopy combined with TD-DFT calculations revealed the nature of the photoisomerization process. Kinetics of the thermal isomerization of <b>C</b> to <b>B</b> and <b>B</b> to <b>A</b> have been studied with ³¹P NMR spectroscopy in CD₂Cl₂, and activation parameters were determined. Isomers <b>A</b> and <b>B</b> have been isolated and crystallographically characterized

Photo- and Thermal Isomerization of (TP)Fe(CO)Cl₂ [TP = Bis(2-diphenylphosphinophenyl)­phenylphosphine]

The title complex displayed structural flexibility via photo- and thermal-isomerization reactions between three isomers: (<i>mer</i>-TP)­Fe­(CO)­Cl₂ (<b>A</b>), <i>unsym</i>-(<i>fac</i>-TP)­Fe­(CO)­Cl₂ (<b>B</b>), and <i>sym</i>-(<i>fac-</i>TP)­Fe­(CO)­Cl₂ (<b>C</b>). Irradiation of <b>A</b> at RT with 525 nm light selectively produces <b>B</b>, while at 0 °C isomer <b>C</b> is formed with the intermediacy of <b>B</b>. UV–vis spectroscopy combined with TD-DFT calculations revealed the nature of the photoisomerization process. Kinetics of the thermal isomerization of <b>C</b> to <b>B</b> and <b>B</b> to <b>A</b> have been studied with ³¹P NMR spectroscopy in CD₂Cl₂, and activation parameters were determined. Isomers <b>A</b> and <b>B</b> have been isolated and crystallographically characterized

Growth and Characterization of PDMS-Stamped Halide Perovskite Single Microcrystals

Recently, halide perovskites have attracted considerable attention for optoelectronic applications, but further progress in this field requires a thorough understanding of the fundamental properties of these materials. Studying perovskites in their single-crystalline form provides a model system for building such an understanding. In this work, a simple solution-processed method combined with PDMS (polydimethyl­siloxane) stamping was used to prepare thin single microcrystals of halide perovskites. The method is general for a broad array of materials including CH₃NH₃PbBr₃, CH₃NH₃PbCl₃, CH₃NH₃Pb­(Br_0.5Cl_0.5)₃, CH₃NH₃Pb­(Br_0.75Cl_0.25)₃, CsPbBr₃, Cs₃Bi₂Br₉, and Cs₃Bi₂I₉. Electron backscatter diffraction (EBSD) was used to investigate the microstructure of the crystals. In order to characterize the microcrystals of CH₃NH₃PbBr₃ electrically, the crystals were grown on prefabricated electrodes creating single-crystal devices contacted from the back. This back-contacted platform circumvents the incompatibility between halide perovskites and the aqueous chemistry used in standard microfabriation processes. It also allows <i>in situ</i> characterization of the perovskite crystal while it operates as a microscopic solar cell

Reaction progress kinetic analysis as tool to reveal ligand effects in Ce(IV)-driven IrCp* catalyzed water oxidation

A series of iridium-based complexes have been evaluated in Ce(IV)-driven water oxidation catalysis. Detailed kinetic data have been obtained from UV–vis stopped-flow experiments, and these data have been analyzed using reaction progress kinetic analysis. The graphical plots show that there are three clear phases in the reaction: catalyst activation, water oxidation catalysis, and cerium concentration controlled catalysis at the end of the reaction. The ligand attached to the IrCp* complex has a clear influence on both the activation as well as the catalysis. Some bidentate ligands result in relatively slow catalysis, and the first-order in iridium supports the presence of mononuclear active species; however, other bidentates form the more active dinuclear species. Monodentate ligands allow the formation of bis-μ-oxo bridged dimeric species, supported by kinetics displaying 1.6-order in [Ir], leading to high reaction rates

Reactivity of a Ruthenium-Carbonyl Complex in the Methanol Dehydrogenation Reaction

Finding new catalysts for the release of molecular hydrogen from methanol is of high relevance in the context of the devel- opment of sustainable energy carriers. Herein, we report that the ruthenium complex Ru(salbinapht)(CO)(P i-Pr 3 ) {salbinapht = 2-[({2’-[(2-hydroxybenzyl)amino]-[1,1 ’ -binaphthalen]-2-yl}imino)- methyl]phenolato} (2) catalyzes the methanol dehydrogenation reaction in the presence of base and water to yield H 2 , for- mate, and carbonate. Dihydrogen is the only gas detected and a turnover frequency up to 55 h 1 at 82 8C is reached. Complex 2 bears a carbonyl ligand that is derived from methanol, as is demonstrated by labeling experiments. The carbony l ligand can be treated with base to form formate (HCOO ) and hydro- gen. The nature of the active species is further shown not to contain a CO ligand but likely still possesses a salen-derived ligand. During catalysis, formation of Ru(CO) 2 (H) 2 (P-iPr 3 ) 2 is oc- casionally observed, which is also an active methanol dehydro- genation catalys

Dibenzo[<i>b</i>,<i>f</i>]phosphepines: Novel Phosphane–Olefin Ligands for Transition Metals

New, stable heterobidentate phosphane–olefin ligands based on the dibenzo­[<i>b</i>,<i>f</i>]­phosphepine backbone are reported together with their redox properties and coordination chemistry to rhodium­(I). The X-ray crystal structures and DFT calculations show different conformations for the <i>P</i>-phenyl (<b>6a</b>) and <i>P</i>-mesityl (<b>6b</b>) derivatives. Cyclic voltammetry (vs Fc/Fc⁺) of <b>6a</b> supported by UV–vis spectroelectrochemistry showed two cathodic waves, a reversible one at <i>E</i>_1/2 = −2.62 V (<i>I</i>_f/<i>I</i>_b = 1.0) and a quasi-reversible (<i>I</i>_f/<i>I</i>_b ≈ 1.2) one at <i>E</i>_1/2 = −3.03 V. Reduction with sodium afforded a mixture of the radical anion [<b>6a</b>^•]⁻, characterized by EPR spectroscopy, and dianion [<b>6a</b>]^2–, for which an X-ray crystal structure was obtained. Both <b>6a</b> and <b>6b</b> bind to Rh^I centers, giving rise to 3:1 (<b>8a</b>) and 2:1 (<b>8b</b>) ligand:Rh complexes, respectively. Two dibenzo­[<i>b,f</i>]­phosphepines in <b>8a</b> and <b>8b</b> act as heterobidentate ligands in which both the phosphorus atom and the olefinic double bond coordinate to rhodium, but the third ligand in <b>8a</b> binds as a monodentate P-donor. The cyclic voltammogram of <b>8b</b> showed two close-lying waves, a one-electron reversible wave at −1.45 V and a two-electron quasi-reversible wave at −1.80 V (<i>I</i>_f/<i>I</i>_b ≈ 1.3). <b>8a</b> showed a reversible wave at −1.71 V and irreversible waves at lower potentials