- Consequences of the protonation of the 19-electron anion [Co(η5-C5H5)(l,5-C8H 12)]-
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The electrochemical and chemical reduction of CoCp(1,5-COD) (1, Cp = η5-C5H5; COD = cyclooctadiene) has been reinvestigated in THF. Whereas the initially formed monoanion 1- (E1/2 = -3.01 V vs Fc, Fc
- Shaw, Michael J.,Eilers, James E.,Geiger, William E.
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- Cobaltocenium acetylsalicylate: synthesis and circular dichroism study of interactions with DNA
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Cobaltocenium acetylsalicylate was synthesized and characterized for the first time. The concentration dependences observed in its interaction with the double helix of DNA have been studied by circular dichroism. In these spectra, changes in the positions and decrease in the intensities of the curves in the positive and negative regions are observed when adding in increasing concentrations of cobaltocenium acetylsalicylate to calf thymus DNA. The observed changes in the effects of Cotton were interpreted as local changes in the conformation of the DNA double helix caused by the interaction of positively charged metallocenium cations with phosphate DNA fragments.
- Snegur,Kaverin,Babievsky
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- Neodymium and dysprosium diiodides in the synthesis of vanadocene and cobaltocene
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The reaction of NdI2 or DyI2 with VCl3 and cyclopentadiene in THF at 65-70°C without isolation of the intermediates afforded vanadocene in 55 and 68% yields, respectively. An analogous reaction of DyI2 with CoCl
- Bochkarev,Burin
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- Fast electron transfer across semiconductor-molecule interfaces: GaAs/Co(Cp)2+/0
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The kinetics of majority electron transfer in the dark from n-GaAs electrodes to cobaltocenium (Co(Cp)2+) acceptors in acetonitrile has been studied in detail, both experimentally and theoretically. The experimental results were obtained from electrochemical impedance spectroscopy, quartz crystal microbalance (QCM and EQCM) studies, and current-potential characteristics. The theoretical work involved calculating the adsorption energy and molecular configuration of the cobaltocenium acceptors at the GaAs surface using high level density functional theory (B3LYP and variations thereof) as well as semiempirical methods. The QCM experiments showed that both Co(Cp)2+ and Co(Cp)20 are physisorbed at GaAs surfaces, with adsorption energies of about 0.2 and 0.4 eV, respectively. The theoretical results are consistent with these experimental results. They indicate that adsorption of the Co(Cp)2+/0 redox system occurs on GaAs, with Co(Cp)20 somewhat more strongly adsorbed than Co(Cp)2+; the Co(Cp)2+/0 molecules were found to adsorb with the cyclopentadienyl rings parallel to the GaAs surface. A model for the overall electron-transfer process was developed that incorporates Co(Cp)2+ adsorption. Analysis of the detailed impedance spectra over the range of 1 Hz to 600 kHz showed that the sequential electron-transfer steps in the model (i.e., electron transfer from the GaAs conduction band to adsorbed Co(Cp)2+, followed by electron transfer from the adsorbed Co(Cp)20 to free Co(Cp)2+ in solution) are very fast and that the observed overall rate of electron transfer is limited by the rate of thermionic emission from the GaAs bulk region to the surface. The implications of these results for the theory of electron transfer at semiconductor-liquid interfaces, and the associated controversies surrounding theory and various experimental results for GaAs-metallocenium systems, are discussed.
- Meier, Andreas,Selmarten, Donald C.,Siemoneit, Kerstin,Smith, Barton B.,Nozik, Arthur J.
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- Synthesis and reactivity of ruthenium complexes with dibenzothiophene and hexahydrodibenzothiophene ligands: Models for catalytic hydrodesulfurization
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As models for the adsorption of dibenzothiophene (DBT) and hexahydrodibenzothiophene (HHDBT) on hydrodesulfurization (HDS) catalysts, the complexes CpRu(DBT)+, CpRu(HHDBT)+, and [(CpRu)2(DBT)]2+ were prepared. I
- Wang, Chia-Mei Jen,Angelici, Robert J.
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- The Orbital-Overlap Factor in Electron Transfer: Sensitivity of Homogeneous Self-Exchange Kinetics for Some Metallocenes to Electronic Structure
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Rate constants, khex, for the electron self-exchange of cobaltocenium-cobaltocene, Cp2Co+/0, and for the decamethyl derivative, (Cp-Me5)2Co+/0, obtained by using the NMR line-broadening technique in acetonitrile and dimethyl sulfoxide are compared with corresponding data for the ferrocene couples Cp2Fe+/0 and (Cp-Me5)2Fe+/0 and for bis(benzene)chromium(I)/(0).The rate constants in a given solvent display a marked sensitivity to the reactant structure, the khex values being about tenfold larger for Cp2Co+/0 relative to Cp2Fe+/0; decamethyl substitution yields tenfold increases in khex for both these couples.A relationship is established between these ca. 100-fold rate variations and the nature of the donor and acceptor orbitals.In particular, the markedly slower self-exchange kinetics observed for Cp2Fe+/0 relative to Cp2Co+/0 are consistent with the much greater ligand-delocalized character of the 4elg orbital involved in the latter electron transfer as compared with the 4e2 or 8alg orbital for the former reaction.The same argument is likely to account for the similar relative rates for (Cp-Me5)2Fe+/0 versus (Cp-Me5)2Co+/0.These rate differences are very unlikely to be due to variations in nuclear reorganization factors since the molecular structures of these couples are virtually identical, and they feature only small differences (ca. 0.3 kcal mol-1) in the inner-shell barriers.The results therefore provide unusually clear evidence for the influence of donor-acceptor electronic coupling in outer-sphere redox reactivity.
- Nielson, Roger M.,Golovin, M. Neal,McManis, George E.,Weaver, Michael J.
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- In situ measurement of the conductivity of polypyrrole and poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium]+ as a function of potential by mediated voltammetry. Redox conduction or electronic conduction?
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The electronic conductivity of polypyrrole and poly[1-methyl-3-(pyrrol-1-ylmethyl)pyridinium]+ (poly-MPMP+) films has been investigated by rotating disk voltammetry. In this in situ measurement, a solution redox species such as cobaltocene, ferrocene, or Cr(2,2′-bipyridine)3+ serves as an electron source at the polymer/solution interface, while electrons are removed at the polymer/electrode interface. The oxidation state of the polymer is controlled by the potential applied to the electrode. The experimental data have been interpreted in terms of both electronic and redox conduction models. A comparison of the results from these two models reveals that the electronic conductivity and the electron diffusion coefficient are related by the Nernst-Einstein equation. It is concluded that electron transport occurs by a hopping mechanism and that the two models are equivalent descriptions of this process in the pyrrole-based polymers. The electronic conductivity of both polymers initially increases linearly with the degree of oxidation of the polymer backbone (concentration of oxidized sites). The conductivity of polypyrrole rises exponentially from 10-8 to 5 × 10-6 Ω-1 cm-1 over the potential range of -0.7 to -0.4 V, while the electron diffusion coefficient remains constant at ca. 10-7 cm2 s-1. At higher potentials the conductivity is too high to be accurately determined by rotating disk voltammetry. The conductivity of poly-MPMP+ increases from ca. 10-9 Ω-1 cm-1 at +0.35 V to ca. 10-4 Ω-1 cm-1 at +1.0 V.
- Mao, Huanyu,Pickup, Peter G.
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- FLASH-VACUUM PYROLYSIS OF η5-CYCLOPENTADIENYLDICARBONYLCOBALT. FORMATION OF COBALTOCENE
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Flash-vacuum pyrolysis (350 deg C, 0.1 Torr) of cyclopentadienyldicarbonylcobalt afforded cobaltocene (85percent yield) at the end of the pyrolysis tube.This compound is formed in a bimolecular reaction in the hot zone of tube between species from which CO ligands have been lost.
- Fiaud, Jean-Claude,Chauvin, Remi,Bloch, Robert
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- Amine-Borane Dehydrogenation and Transfer Hydrogenation Catalyzed by α-Diimine Cobaltates
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Anionic α-diimine cobalt complexes, such as [K(thf)1.5{(DippBIAN)Co(η4-cod)}] (1; Dipp=2,6-diisopropylphenyl, cod=1,5-cyclooctadiene), catalyze the dehydrogenation of several amine-boranes. Based on the excellent catalytic properties, an especially effective transfer hydrogenation protocol for challenging olefins, imines, and N-heteroarenes was developed. NH3BH3 was used as a dihydrogen surrogate, which transferred up to two equivalents of H2 per NH3BH3. Detailed spectroscopic and mechanistic studies are presented, which document the rate determination by acidic protons in the amine-borane.
- Maier, Thomas M.,Sandl, Sebastian,Shenderovich, Ilya G.,Jacobi von Wangelin, Axel,Weigand, Jan J.,Wolf, Robert
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supporting information
p. 238 - 245
(2019/01/04)
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- A process for preparing [...]
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The invention provides a preparation technology of cobaltocene. The preparation technology comprises the following steps: (1) reacting cobalt dichloride with a metal compound containing alkyloxy in an oxygen-free first alcoholic solvent to obtain a cobalt compound containing alkyloxy; (2) reacting the alkyloxy-containing cobalt compound obtained in the step (1) with a cyclopentadiene monomer in a second alcoholic solvent to obtain a mixed solution containing cobaltocene, and carrying out distillation to remove the solvent to obtain a coarse product of cobaltocene; (3) dissolving the cobaltocene coarse product obtained in the step (2) into a non-proton solvent, filtering, adding an ether solvent into the condensed filtrate, and carrying out recrystallization to obtain cobaltocene solids. The raw materials used in the provided preparation technology all have a wide source and low price. The reagents, which need strict reaction conditions, such as metal sodium, amino sodium, and the like, are not used in the provided preparation technology. Moreover, the reaction conditions are mild, the operation is convenient and safe, the production cost is low, thus the preparation technology is very suitable for industrial production, and the cobaltocene product is high-purity solid crystals.
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Paragraph 0029-0056
(2019/03/29)
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- Direct synthesis of an anionic 13-vertex closo-cobaltacarborane cluster
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Reaction of 1,2-bis(diphenylphosphino)-ortho-carborane (L) with [K(thf){(MesBIAN)Co(η4-cod)}] (1, MesBIAN = bis(mesityliminoace-naphthene)diimine, cod = 1,5-cyclooctadiene) affords an anionic 13-vertex closo-cobaltacarborane cluster (2) in one step. The mechanism of this transformation has been studied by experimental and quantum chemical techniques, which suggest that a series of outer-sphere electron transfer and isomerisation processes occurs. This work shows that low-valent metalate anions are promising reagents for the synthesis of anionic metallacarborane clusters.
- Maier, Thomas M.,Coburger, Peter,Van Leest, Nicolaas P.,Hey-Hawkins, Evamarie,Wolf, Robert
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supporting information
p. 15772 - 15777
(2019/11/11)
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- Direct probing of photoinduced electron transfer in a self-assembled biomimetic [2Fe2S]-hydrogenase complex using ultrafast vibrational spectroscopy
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A pyridyl-functionalized diiron dithiolate complex, [μ-(4-pyCH 2-NMI-S2)Fe2(CO)6] (3, py = pyridine (ligand), NMI = naphthalene monoimide) was synthesized and fully characterized. In the presence of zinc tetraphenylporphyrin (ZnTPP), a self-assembled 3·ZnTPP complex was readily formed in CH2Cl2 by the coordination of the pyridyl nitrogen to the porphyrin zinc center. Ultrafast photoinduced electron transfer from excited ZnTPP to complex 3 in the supramolecular assembly was observed in real time by monitoring the (C≡O) and (C=O)NMI spectral changes with femtosecond time-resolved infrared (TRIR) spectroscopy. We have confirmed that photoinduced charge separation produced the monoreduced species by comparing the time-resolved IR spectra with the conventional IR spectra of 3?- generated by reversible electrochemical reduction. The lifetimes for the charge separation and charge recombination processes were found to be τCS = 40 ± 3 ps and τCR = 205 ± 14 ps, respectively. The charge recombination is much slower than that in an analogous covalent complex, demonstrating the potential of a supramolecular approach to extend the lifetime of the charge-separated state in photocatalytic complexes. The observed vibrational frequency shifts provide a very sensitive probe of the delocalization of the electron-spin density over the different parts of the Fe2S2 complex. The TR and spectro-electrochemical IR spectra, electron paramagnetic resonance spectra, and density functional theory calculations all show that the spin density in 3?- is delocalized over the diiron core and the NMI bridge. This delocalization explains why the complex exhibits low catalytic dihydrogen production even though it features a very efficient photoinduced electron transfer. The ultrafast porphyrin-to-NMI-S2-Fe2(CO)6 photoinduced electron transfer is the first reported example of a supramolecular Fe2S2-hydrogenase model studied by femtosecond TRIR spectroscopy. Our results show that TRIR spectroscopy is a powerful tool to investigate photoinduced electron transfer in potential dihydrogen-producing catalytic complexes, and that way to optimize their performance by rational approaches.
- Li, Ping,Amirjalayer, Saeed,Hartl, Frantisek,Lutz, Martin,Bruin, Bas De,Becker, Rene,Woutersen, Sander,Reek, Joost N. H.
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p. 5373 - 5383
(2014/06/09)
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- One-electron redox reactions involving chromium(0) and molybdenum(0) bis-1,3,5-trimethylbenzene derivatives
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The reaction of M(η6-1,3,5-Me3C6H3)2, M = Cr, Mo, with the tetrahalides of Groups 4 and 5 elements proceeds with the monoelectronic oxidation of the metal bis-arene to the [M(η6-Me3/s
- Englert, Ulli,Pampaloni, Guido,Puccini, Filippo,Volpe, Manuel
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p. 3144 - 3150
(2008/02/09)
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- Synthesis and reaction behaviour of {[Hf](μ-σ,π-C≡CR) 2}Ni(CO); the solid-state structure of [(η5-C 5H4SiMe3)2Hf(C≡C tBu)]2O
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The synthesis of the heterobimetallic hafnium(IV)-nickel(0) complexes {[Hf](μ-σ,π-C≡CR)2}Ni(CO) (3a, [Hf] = (η5-C5H5)2Hf, R = Ph; 3b, [Hf] = (η5-C5H4SiMe3)2Hf, R = tBu) in which an early (Hf) and a late (Ni) transition metal atom are bridged by σ- and π-bound alkynyl groups succeeds by treatment of [Hf](C≡CR)2 (1a, [Hf] = (η5-C5H 5)2Hf, R = Ph; 1b, [Hf] = (η5-C 5H4SiMe3)2Hf, R = tBu) with equimolar amounts of Ni(CO)4 (2). The reaction chemistry of 1 and 3 towards different substrates is discussed. Treatment of 3b with P(OMe)3 (4a) affords the mononuclear nickel monocarbonyl complex Ni(CO)[P(OMe)3]3 (5), while the reaction of 1a or 1b with MCl2 (6a, M = Fe; 6b, M = Ni; 6c, M = Co) produces by an cyclopentadienyl transfer from hafnium to M the sandwich compounds (η5-C5H4R')2M (M = Fe: 7a, R' = H; 7b, R' = SiMe3; M = Ni: 7c, R' = H; 7d, R' = SiMe3; M = Co: 7e, R' = H). Addition of KOH to 1b or 3b, respectively, affords the homobimetallic hafnium complex {[Hf](C≡CR)}2O (8) in which two [Hf](C≡CR) fragments are bridged by an oxygen atom. Possible reaction mechanisms for the formation of 5, 7 and 8 by starting from 1 or 3 will be given. The result of the X-ray structure analysis of 8 is reported. Complex 8 crystallises in the monoclinic space group C2/c with the cell parameters a = 24.437(8), b = 14.655(5), c = 14.123(4) A?, β = 101.67(2)°, V = 4953(3) A?3, Z = 4 and D = 1.454 g cm-3. Complex 8 contains a linear Hf-O-Hf unit with pseudo-tetrahedral coordinated hafnium atoms.
- Kralik, Joachim,K?hler, Katrin,Rüffer, Tobias,Lang, Heinrich
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p. 1185 - 1191
(2007/10/03)
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- Improvements in the preparation of cyclopentadienyl thallium and methylcyclopentadienylthallium and in their use in organometallic chemistry
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Improved preparation methods of cyclopentadienylthallium and methylcyclopentadienylthallium, giving quantitative yields and incorporating ultrasound techniques, are described. Their use as starting materials for a wide range of organometallic syntheses is discussed and demonstrated.
- Neto, Alberto Federman,Borges, Aurea Donizete Lanchote,Miller, Joseph,Darin, Vitor Andre
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p. 1299 - 1314
(2008/10/09)
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- Interaction between cobaltocenium and decamethylcobaltocenium salts and Ph3ELi (E = Si, Ge, Sn)
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Reactions of cobaltocenium salts (C5R5)2Co]PF6 (R = H, Me) with PhjELi (E = Si, Ge, Sn) and with Pf-4SbLi mainly follow two pathways (nucleophilic addition and oneelectron reduction), yielding cobalt cyclopentadiene-cyclopentadienyl complexes (
- Maryin,Petrovskii,Krasilmkova
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p. 2427 - 2430
(2007/10/03)
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- XX. The synthesis of YbCp2Cl(THF)0.5 (Cp=cyclopentadienyl; THF=tetrahydrofuran), YbCp2X(THF) (X=Br or I), and (YbCp2X)2 (X=Cl, Br or I) by oxidation of YbCp2 with metal and organic halides, and the determination of the X-ray structure of YbCp2I(THF)
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Reaction of YbCp2(DME) (Cp=cyclopentadienyl; DME=1,2-dimethoxyethane) with MCl2 (M=Hg, Cd, Zn, Pb, Sn, Cu, Pd, or Co) or MCl (M=Ag, Cu or Tl) in tetrahydrofuran (THF) gives the metal M and YbCp2Cl(YHF)0.5, generally in excellent yield, with small amounts of TlCp and CoCp2 also detected from TlCl and CoCl2 respectively.Similarly, YbCp2X(THF) (X=Br or I) and YbCp2Cl(DME)0.5 have been prepared in good yields analogous oxidation with suitable mercury(II) halides.However YbCp2(DME) and FeCl3 yield ferrocene.In simpler syntheses, YbCp2X(THF)n (X=Cl, n=0.5; X=Br or I, n=1) have been obtained by reactions of YbCp2(DME) with C2Cl6 or (CH2X)2 (X=Br or I) in THF, and (YbCp2X)2 by analogous reactions of unsolvated YbCp2 in petroleum ether.The X-ray crystal structure of YbCp2I(THF) (monocyclic, P21/c, a=8.147(1), b=13.788(2), c=14.149(3) Angstroem, β=105.56(1) deg, Z=4, R=0.042, for 2324 observed data) shows the complex to be monomeric with formal eight coordination for ytterbium, and with a pseudo-tetrahedral array of the centroids of the Cp rings, oxygen, and iodine ( 2.565 Angstroem, Yb-O 2.311(5) Angsrtoem, Yb-I 2.9316(7) Angstroem). - Keywords: ytterbium; cyclopentadienyl; oxidation; rare earth; crystal structure; lanthanide
- Deacon, Glen B.,Harris, Stuart C.,Meyer, Gerd,Stellfeldt, Dirk,Wilkinson, Dallas L.,Zelesny, Gerd
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p. 247 - 254
(2007/10/03)
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- The preparation of finely divided metal powders and transition metal complexes using organically solvated magnesium
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Treatment of commercial magnesium powder in THF with a small amount of anthracene generates a highly active form of magnesium (Mg*).The Mg* is an excellent in situ reducing agent for transition metal salts, giving highly reactive metal powders of Groups 8-12.In the presence of electron donor ligands, this reduction provides a useful one-step route to organotransition metal complexes.The application of 35 kHz ultrasound during the reaction improves the dispersity of the metal powders and enhances the yields of the complexes.
- Boennemann, Helmut,Bogdanovic, Borislav,Brinkmann, Rainer,Spliethoff, Bernd,He, Da-Wei
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- Charge-Transfer Ion Pairs. Structure and Photoinduced Electron Transfer of Carbonylmetalate Salts
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Brightly colored crystals, readily isolated from such colorless carbonylmetalates as Co(CO)4(1-), Mn(CO)5(1-), and V(CO)6(1-) in conjunction with various metallocenium and pyridinium cations, are identified as charge-transfer (CT) salts by their unambiguous absorption and diffuse reflectance spectra.X-ray crystallography of such CT salts establishes the relevant interionic separations, the spatial cation/anion orientations, as well as the deviations from tetrahedral Co(CO)4(1-) configuration that are all inherent to the charge-transfer interaction of intimate ion pairs.The Co(CO)4(1-) distortions, as observed in the crystal structures, are also revealed by their characteristic carbonyl IR spectra.The persistence of the unique carbonyl IR and charge-transfer absorption bands in nonpolar solvents thus leads to contact ion pairs (CIP) that are closely related or structurally the same as those elucidated by X-ray crystallography.Accordingly, the charge-transfer excitation of contact ion pairs can be examined directly in solution by time-resolved spectroscopy.The spectral observation of the radical pair .> from the 532-nm excitation of the charge-transfer salt with a 10-ns laser pulse represents the experimental verification of Mulliken theory.As such, the efficient scavenging of such labile 17-electron carbonylmetal radicals as Co(CO)4. and Mn(CO)5. affords a rich menu of productive photochemistry attendant upon the charge-transfer excitation of contact ion pairs.
- Bockman, T. M.,Kochi, J. K.
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p. 4669 - 4683
(2007/10/02)
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- Reduction of CO2 and other substrates using photochemical reactions of the W2(CO)102- complex
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The photochemistry of the W2(CO)102- complex was investigated with the goal of determining if irradiation of this dimer generates a powerful reducing agent, presumably a 19-electron species. In general, the photochemistry of the W2(CO)102- complex is comparable to that of other metal-metal-bonded carbonyl dimers. Irradiation into the low-energy tail of the d π → σ* electronic transition of the W2(CO)102- complex led to W-W bond homolysis. The resulting 17-electron W(CO)5- radicals could be trapped with suitable ligands such as 4-cyanopyridine to give 19-electron adducts . (See ref 3 for an important definition of the phrase 19-electron adduct .) Evidence is presented that the ligands PPh3 and PBu3 also react with photogenerated W(CO)5- to form adducts: W(CO)5- + PR3 → W(CO)5PR3-. These adducts are powerful reducing agents, and they were used to reduce CO2 to formate and CO. The only organometallic product formed in the reaction was W(CO)5PPh3, the oxidized form of the 19-electron complex. In a similar manner, Mn2(CO)10 was reduced to Mn(CO)5-, Cp2Co+ to Cp2Co, benzophenone to the radical anion, and methylviologen (MV2+) to MV+. Alternative reduction mechanisms involving the W(CO)5- radical, W(CO)52-, or HW2(CO)10- as reductants were shown not to be operating. Nineteen-electron complexes generated by irradiation of Cp2Mo2(CO)6 proved incapable of reducing CO2.
- Silavwe, Ned D.,Goldman, Alan S.,Ritter, Robin,Tyler, David R.
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p. 1231 - 1236
(2008/10/08)
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- Photoredox reaction of cobalticinium pentacarbonylmanganate(-I) induced by outer-sphere metal to metal charge transfer excitation
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The salts +- and +- show long-wavelength absorptions at λmax 749 nm and 665 nm.These bands are assigned to metal to metal charge transfer (MMCT) transitions from Mn-I to CoIII and CrI.Upon MMCT excitation the former ion pair is converted to Co(C5H5)2 and Mn2(CO)10.The latter ion pair undergoes an analogous redox reaction as a thermal process.The thermal and the light-induced electron transfer are explained on the basis of the Hush model.
- Kunkely, Horst,Vogler, Arnd
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p. C29 - C43
(2007/10/02)
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- Kinetics and mechanism of the reduction of protons to hydrogen by cobaltocene
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The rate constant kobsd for the overall reaction 2CoCp2 + 2H+ → 2CoCp2+ + H2 (eq i) was determined by pulse radiolysis in an aqueous sulfuric acid medium for cobaltocene (1), 1,2,3,4,5-pentamethylcobaltocene (2), and decamethylcobaltocene (3). The reaction is first order in 1 and in protons with k2,obsd = 42 ± 1.5 s-1 M-1 at cH+ = 8 × 10-3-4.7 × 10-1 M. Possible mechanistic pathways for eq i are discussed, and a second-order disproportionation of protonated 1 or a mechanism that involves reduction of protonated 1 by unprotonated 1 is best compatible both with the observed kinetics and with chemical evidence. Deuteriation experiments show protonation to occur exclusively at the metal.
- Koelle,Infelta,Gr?tzel
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p. 879 - 883
(2008/10/08)
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- Solvent Dynamical Effects in Electron Transfer: Comparisons of Self-Exchange Kinetics for Cobaltocenium-Cobaltocene and Related Redox Couples with Theoretical Predictions
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Rate constants, Kex, and activation parameters for the self-exchange of cobaltocenium-cobaltocene Cp2Co+/0, and the decamethyl derivative Cp'2Co+/0, in 13 organic solvents have been evaluated by using the proton NMR line-broadening technique with the objective of probing the influence of solvent dynamics upon the electron-transfer kinetics.Together with some corresponding measurements reported earlier for ferrocenium-ferrocene Cp2Fe+/0, additional measurements for the decamethyl derivative, Cp'2Fe+/0, and with corresponding data for Cp2Co+/0 electrochemical exchange, these results enable a systematic comparative examination to be made of the effects of solvent dielectric relaxation on the barrier-crossing frequency for such simple outer-sphere reactions.For the facile Cp'2Co+/0 couple the solvent dependence of the observed frequency factors, νn(obsd), extracted from the kex values by correcting for the solvent-dependent barrier height, ΔG*, is in approximate accordance with the relative frequency factors νos(calcd), predicted from the continuum model of overdamped solvent relaxation.The subunity (ca. 0.7-0.8) slope of the logarithmic νn(obsd) - ??os(calcd) plot for Cp'2C0+/0 self-exchange is consistent with a recent theoretical prediction of the combined effect of overdamped solvent motion and reactant vibrations (ref 2g).In a given solvent, the sequence of kex values is Cp'2Co+/0 > Cp2Co+/0 ca.Cp'2Fe+/0 > Cp2Fe+/0, with Cp2Co+/0 and Cp2Fe+/0 being about 10- and 100-folds lower, respectively, than Cp'2Co+/0 self-exchange.While these reactivity differences can be traced to variations in donor-acceptor orbital overlap, the solvent dependencies of kex for Cp2Co+/0 and Cp2Fe+/0 electron exchange nevertheless exhibit a strong influence from overdamped solvent relaxation.Marked deviations from the dielectric continuum predictions are seen, however, in several solvents.Thus the barrier-crossing frequencies in propylene carbonate, N-methylformamide, and especially methanol are substantially (4-100-fold) larger than expected from νos(calcd), implicating the presence of surprisingly rapid relaxation modes in these solvents.The solvent-dependent activation parameters also differ significantly from the expectations of conventional theoretical modes.
- Nielson, Roger M.,McManis, George E.,Golovin, Neal M.,Weaver, Michael J.
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p. 3441 - 3450
(2007/10/02)
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- Reactivity of germylmercurate complexes
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The selective insertion of sulfur into the Ge-Hg bond in the ionic complex 3Hg>-Cp2CO+ results in the formation of mono-, di- and trithiolate derivatives.The compounds have been characterized by elementary analysis, IR, 19F and 199Hg NMR spectroscopy.The molecular structure of 3>--Cp2Co+ has been determined by X-ray analysis.Sulfur-containing complexes are donors of chalcogen atoms in the reactions with covalent and ionic polynuclear organometallic compounds.Ytterbium dicyclopentadienide and vanadocene displace cobaltocene from 2HgI>-Cp2Co+, and Cp2Co removes thallium from its germylmercurate complex.A general scheme for the reaction of vanadocene with cobalticinium germylmercurate has been proposed.The zerovalent triphenylphosphine complex of platinum Pt(PPh3)4 destroys the ionic structure of 2HgI>-(C6H6)2Cr+ to give dibenzenechromium iodide and a polinuclear compound with Ge-Hg-Pt-Ge chain.
- Pankratov, L. V.,Penyagina, I. M.,Zakharov, L. N.,Bochkarev, M. N.,Razuvaev, G. A.,et al.
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p. 313 - 322
(2007/10/02)
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- Nineteen-electron adducts in the photochemistry of Cp2Fe2(CO)4 (Cp = η5-C5H5)
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Cp2Fe2(CO)4 is apparently different from the other metal-metal-bonded carbonyl dimers in that irradiation of this dimer in the presence of ligands does not lead to disproportionation: Cp2Fe2(CO)4 + L + hv ? CpFe(CO)2- + CpFe(CO)3-nLn+. However, it was demonstrated that with most ligands the disproportionation reaction does occur but the back-reaction of the products is facile. The back-reaction can be prevented by reacting further one of the products. For example, in CH2Cl2 solution, CpFe(CO)2- reacts with the solvent to give CpFe(CO)2CH2Cl and the back-reaction is prevented. The mechanism of the disproportionation reaction is proposed to be a chain mechanism involving 19-electron adducts formed by the reaction of a 17-electron metal radical with a ligand, e.g. CpFe(CO)2 + L → CpFe(CO)2L. It is demonstrated that the 19-electron adducts are powerful reductants. The following organometallic, organic, and inorganic substrates were reduced by the 19-electron species, thereby demonstrating the versatility of these species as reducing agents: CpMo(CO)3Cl, Fe(CN)63-, Mn2(CO)10, Re2(CO)10, Ru3(CO)12, Fe(CO)5, N-n-butylpyridinium, and Cp2Co+. Experiments involving the reduction of Cp2Co+ demonstrated several mechanistic points concerning the reactivity of 19-electron species.
- Goldman, Alan S.,Tyler, David R.
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p. 253 - 258
(2008/10/08)
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- (Cyclopentadienyl)organylcobalt Complexes
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Reaction of cobalticinium chloride (1) with organometallic compounds of Li, Mg, Al, and Zn leads (depending upon the metal, the organic group, the solvent, and the reaction temperature) to the formation of the (η5-cyclopentadienyl)(η4-5-organyl-1,3-cyclopentadiene)cobalt complexes 4a - j or cobaltocene (2) or mixtures of both.The exclusive formation of the exo-5-organyl derivatives 4 suggests a mechanism involving a cobalticinium chloroorganometallate species 3 or a cobalticinium alkanide species C.Complexes 3 were isolated from the reaction with aluminium or zinc compounds.Solvated cobalticinium salts of type C were identified in the reactions of 1 with sodium methoxide or ethoxide.They react further to (η5-cyclopentadienyl)(η4-exo-5-alkoxy-1,3-cyclopentadiene)cobalt complexes 6 upon removing the solvating alcohol. - In contrast to the unstable bis(cyclopentadienyl)organylcobalt complexes B (which react further to 2), the corresponding organylcobalt complexes 8a - f were obtained from the reaction of (η3-allyl)(η5-cyclopentadienyl)cobalt bromide 7 with organolithium or -magnesium halides.At 20 deg C 8d isomerizes by coupling of the vinyl and the allyl group into the (η4-1,3-pentadiene)cobalt complexes 9a and b.
- Lehmkuhl, Herbert,Nehl, Hans Friedrich
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p. 3443 - 3456
(2007/10/02)
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- CoCpBr INTERMEDIATES IN THE CYCLOPENTADIENYLATION OF CoBr2 WITH NaCp
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Reaction of CoBr2 and NaCp (Cp = η5-C5H5) at low temperature followed by addition of a diene or acetylene gives the complexes CoCp(diene).The scope and mechanism of this novel reaction have been investigated.
- Koelle, U.,Sistig, F.,Gersdorf, J.
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p. 253 - 258
(2007/10/02)
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- Photochemical reactions of a cobaltacyclopentadiene and the molecular structure of (η5 Cyclopentadienyl)
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Least-squre refinement on 177 variables led to a final value of the R index on of unique observations; the conventional R index on observations having bond.
- Trogler, Willam C.,Ibers, James A.
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p. 536 - 542
(2008/10/08)
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- The reaction of molten magnesium cyclopentadienide with fluorides and other metal halides
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Molten magnesium cyclopentadienide in the absence of solvent reacts with a large number of metal halides, and in particular fluorides, to give cyclopentadienyl metal compounds, frequently in good yield. The reaction is particularly suited to the preparation of the cyclopentadienyls of thorium, uranium, scandium, and the rare earths from their fluorides, which are readily accessible and relatively stable to moisture.
- Reid,Wailes
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p. 1213 - 1216
(2008/10/08)
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