Linear Dimerization of Terminal Alkynes by Bis(tetramethylphenylcyclopentadienyl)titanium-Magnesium Hydride and Acetylide Complexes

2003 ◽  
Vol 68 (10) ◽  
pp. 1877-1896 ◽  
Author(s):  
Karel Mach ◽  
Róbert Gyepes ◽  
Michal Horáček ◽  
Lidmila Petrusová ◽  
Jiří Kubišta
Keyword(s):  
Electron Spin Resonance ◽  
Crystal Structures ◽  
Electron Spin ◽  
Esr Spectra ◽  
Magnesium Hydride ◽  
Terminal Alkynes ◽  
Turnover Number ◽  
Hydride Complexes ◽  
Spin Resonance ◽  
Linear Dimerization

New tetramethylphenylcyclopentadienyl trinuclear titanocene hydride-magnesium hydride complexes [{Ti(η5-C5Me4R)2(μ-H)2}2Mg], where R = Ph (1) or 4-fluorophenyl (FPh; 2), the dinuclear [Ti(η5-C5Me4Ph)[η5:η1{Ti:Mg}-C5Me4(o-C6H4)](μ-H)2Mg(THF)2] (3) and [Ti(η5-C5Me4Ph)2(μ-H)2MgC(Me)=CHMe] (4) complexes, and the [{Ti(η5-C5Me4Ph)2(η1-C≡CSiMe3)2}-{MgCl(THF)}+] (5) tweezer complex initiated the dimerization of (trimethylsilyl)ethyne (TMSE) or 1-hexyne (HXYN) to exclusively head-to-tail (HTT) dimers at 60 °C with the turnover number ranging from 300 to 500 mol alkyne per mol of the Ti complex. In contrast, all of them were inactive in the dimerization of tert-butylethyne (TBUE). Monitoring of reactions of the 1-5 complexes with the alkynes by electron spin resonance (ESR) method revealed a decay of the initial complexes 1-5 in the dimerizing systems with TMSE and HXYN or a conversion of complexes 3, 4, and 5 into the Ti(III) acetylide [Ti(η5-C5Me4Ph)2(η1-C≡CCMe3)] (6) in systems with TBUE. The acetylide 6 also initiated the dimerization of TMSE and HXYN to HTT dimers only. This fact together with the absence of ESR signals of tweezer complexes and acetylides in the reacting hydride systems allow us to assume that the rate of conversion of complexes 1-4 to tweezer complexes is slower than the rate of dissociation of the tweezer complexes to give the acetylides which are apparently the ultimate catalytic species. Most of the evidence on the catalytic complexes has been obtained from ESR spectra which are reliably characteristic of each type of the complexes. Crystal structures of 4 and 6 were determined.

FREE RADICALS OF BIOLOGICAL INTEREST: PART II. ELECTRON SPIN RESONANCE (ESR) SPECTRA OF 2537 A IRRADIATED AMINO ACIDS

1967 ◽  
Vol 45 (12) ◽  
pp. 1831-1839 ◽  
Author(s):  
W. F. Forbes ◽  
P. D. Sullivan
Keyword(s):  
Amino Acids ◽  
Electron Spin Resonance ◽  
Electron Spin ◽  
Hydrogen Abstraction ◽  
Esr Spectra ◽  
Side Chain ◽  
Biological Interest ◽  
Spin Resonance ◽  
Cyclohexadienyl Radical ◽  
Secondary Radical

Polycrystalline amino acids, when irradiated with 2537 Å light, afford a variety of electron spin resonance signals. These signals are generally stable at room temperature for relatively long periods of time. For a number of the spectra obtained, there is evidence that more than one radical species contributes to the observed spectra. The signals obtained frequently differ from those obtained on exposure to ionizing radiation. The postulated species formed can often be visualized as being formed by effective hydrogen abstraction from the alkyl-substituted tertiary carbon atom or from the —OH, —SH or —NH group contained in the side chain. For L-phenylalanine a secondary radical is obtained, which is ascribed to a cyclohexadienyl radical.

Electron spin resonance observations of photochemically generated contact ammonium ion-pairs of fluoro-substituted ketones

1979 ◽  
Vol 57 (5) ◽  
pp. 600-602 ◽  
Author(s):  
K. S. Chen ◽  
T. Foster ◽  
J. K. S. Wan
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Ion Pairs ◽  
Esr Spectra ◽  
Ammonium Ion ◽  
Spin Resonance ◽  
Photochemical Systems

Contact radical ion-pairs of ammonium and fluoro-substituted ketones were generated in photochemical systems and their here-to-fore elusive esr spectra were characterized.

Electron Spin Resonance Investigations on Perovskite Solar Cell Materials Deposited on Glass Substrate

MRS Advances ◽  
2018 ◽  
Vol 3 (32) ◽  
pp. 1831-1836
Author(s):  
C. L. Saiz ◽  
E. Castro ◽  
L. M. Martinez ◽  
S. R. J. Hennadige ◽  
L. Echegoyen ◽  
...  
Keyword(s):  
Electron Spin Resonance ◽  
Solar Cell ◽  
Line Width ◽  
Electron Spin ◽  
Glass Substrate ◽  
Esr Spectra ◽  
Perovskite Solar Cell ◽  
Hole Transport ◽  
Ex Situ ◽  
Spin Resonance

ABSRTACTIn this article, we report low-temperature electron spin resonance (ESR) investigations carried out on solution processed three-layer inverted solar cell structures: PC61BM/CH3NH3PbI3/PEDOT:PSS/Glass, where PC61BM and PEDOT:PSS act as electron and hole transport layers, respectively. ESR measurements were conducted on ex-situ light (1 Sun) illuminated samples. We find two distinct ESR spectra. First ESR spectra resembles a typical powder pattern, associated with gx = gy = 4.2; gz = 9.2, found to be originated from Fe3+ extrinsic impurity located in the glass substrate. Second ESR spectra contains a broad (peak-to-peak line width ∼ 10 G) and intense ESR signal appearing at g = 2.008; and a weak, partly overlapped, but much narrower (peak-to-peak line width ∼ 4 G) ESR signal at g = 2.0022. Both sets of ESR spectra degrade in intensity upon light illumination. The latter two signals were found to stem from light-induced silicon dangling bonds and oxygen vacancies, respectively. Our controlled measurements confirm that these centers were generated during UV-ozone treatment of the glass substrate –a necessary step to be performed before PEDOT:PSS is spin coated. This work forms a significant step in understanding the light-induced- as well as extrinsic defects in perovskite solar cell materials.

Microscopic Study of Metal Hydrides using Electron Spin resonance

1980 ◽  
Vol 3 ◽  
Author(s):  
E. L. Venturini
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Metal Hydrides ◽  
Esr Spectra ◽  
Spectroscopic Technique ◽  
Host Lattice ◽  
Hydrogen Ions ◽  
Spin Resonance ◽  
Symmetry Phase ◽  
Paramagnetic Ions

ABSTRACTElectron spin resonance (ESR) of dilute paramagnetic ions in nonmagnetic metallic hydrides provides microscopic information about the hydrogen ions in the immediate vicinity of the impurity. By comparing ESR spectra for different host metals and several hydrogen/metal ratios, one can determine material properties including host lattice symmetry, phase boundaries and occupation of available sites by hydrogen. Examples are presented of ESR of dilute Er in group IIIB and IVB metal hydrides, demonstrating the sensitivity and versatility of ESR as a spectroscopic technique.

An ESR and calorimetric study of iron oolitic samples from the Northampton ironstone

Clay Minerals ◽  
1990 ◽  
Vol 25 (3) ◽  
pp. 303-311 ◽  
Author(s):  
A. U. Gehring ◽  
R. Karthein
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Hyperfine Splitting ◽  
Esr Spectroscopy ◽  
Thermal Conversion ◽  
Esr Spectra ◽  
Calorimetric Study ◽  
Calorimetric Methods ◽  
Mineral Phases ◽  
Spin Resonance

AbstractElectron spin resonance (ESR) spectroscopy and calorimetric methods were used to characterize conversion processes in multimineral samples from the Northampton ironstone (NIS) at temperatures between 25°C and 800°C. The beginning of the thermal conversion processes can be determined by the formation of asymmetric ESR spectra with g ≈ 2 at 250°C. The breakdown of the berthierine structure between 250°C and 520°C is indicated by the disappearance of the hyperfine splitting in the Mn2+ spectrum and the formation of magnetite. The decomposition of siderite and calcite was found by calorimetric methods at 580°C and 700°C, respectively. The hematite formation between 550°C and 800°C is explained by the decomposition of siderite but also by the oxidation of previously formed magnetite. The occurrence of hematite as the dominant ferric oxide at 800°C signifies the end of the conversion process of the major mineral phases in the NIS samples.

Nitroxide derivatives of acetylacetone as spin-labelled ligands

1981 ◽  
Vol 59 (1) ◽  
pp. 156-163 ◽  
Author(s):  
D. Plancherel ◽  
D. R. Eaton
Keyword(s):  
Electron Spin Resonance ◽  
Metal Complex ◽  
Electron Spin ◽  
Hyperfine Coupling ◽  
Esr Spectra ◽  
Enol Form ◽  
Coupling Constants ◽  
Spin Resonance ◽  
Steric Factors ◽  
Derivatives Of

Electron spin resonance spectra are reported from a number of radicals derived from 2,4-pentadione substituted at the 3 position with nitroxide-containing groups. If the substituent is t-butyl nitroxide no metal complexes are formed. This is attributed to steric factors which prevent the formation of the enol form of the β-diketone. If the substituent is trifluoromethyl nitroxide two types of metal complex have been observed. The esr spectra of the first type are very similar to that of the uncomplexed radical. Such complexes are formed with Co(III) and Al(III). The esr spectra of the second type show considerably increased 14N and 19F hyperfine coupling constants and in some cases large couplings to the metal nucleus. Complexes for the second type have been observed with Pd(II), Pt(II), and Rh(III). The possible structures of these radicals are discussed.

The Resolution Enhancement of Electron Spin Resonance Spectra by Self-Deconvolution with a Finite Impulse Response Operator

1983 ◽  
Vol 37 (1) ◽  
pp. 67-72 ◽  
Author(s):  
Kazuo Shimokoshi ◽  
R. Norman Jones
Keyword(s):  
Electron Spin Resonance ◽  
Impulse Response ◽  
Electron Spin ◽  
Finite Impulse Response ◽  
Resolution Enhancement ◽  
Esr Spectra ◽  
Ethanol Solution ◽  
General Function ◽  
Response Operator ◽  
Spin Resonance

The method of self-deconvolution is applied to the resolution enhancement of electron spin resonance spectra (ESR). The component lineshapes of ESR spectra are basically Lorentzian, but they often carry strong Gaussian perturbations. Deconvolution with a finite impulse response operator filter to enhance the resolution of Lorentzian and Gaussian ESR band envelopes is discussed and a more general function is derived for Gauss-Lorentz convolute (Voigt) lineshapes. The method is applied initially to the simulated isotropic ESR spectrum of the ethyl radical in the liquid state and to a simulated anisotropic spectrum of a crystalline powder. Application to real spectra is illustrated by the anisotropic spectrum of bis(acetylacetonato)-copper(II) [Cu(AcAc)2] in ethanol solution at 140 K in order to resolve the hyperfine lines. The perpendicular component of this spectrum is notable for its poor resolution.

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