Recent experiments with transient NMRON

High resolution magnetic and electric hyperfine interaction distributions are determined for single crystal⁵⁴MnNi with diffused impurity concentrations of 0.14 and 0.40 at%, and for a 0.1 µm layer of⁶⁰CoFe co-plated onto single crystal Fe. High quality gamma detected nuclear spin echoes recorded for the⁶⁰CoFe specimen demonstrate that a reduced influence of the RF skin effect far outweighs any magnetic hyperfine field interaction broadening associated with the co-plating process.     

The Nature of Line Broadening in Thermally Detected 57FeFe NMR

⁵⁷FeFe with isotopic concentrations from 15 to 95% is studied using NMR thermally detected by nuclear orientation. Lines are found to be consistently homogeneous. The contrast with previous inhomogeneous ⁵⁷FeFe lines from Mössbauer detected NMR is explained by differences in radio frequency field strength.     

Terminal Alkyne Coupling Reactions through a Ring: Mechanistic Insights and Regiochemical Switching

The mechanism and selectivity of terminal alkyne coupling reactions promoted by rhodium(I) complexes of NHC‐based CNC pincer ligands have been investigated. Synthetic and kinetic experiments support E‐ and gem‐enyne formation through a common reaction sequence involving hydrometallation and rate‐determining C?C bond reductive elimination. The latter is significantly affected by the ligand topology: Employment of a macrocyclic variant enforced exclusive head‐to‐head coupling, contrasting the high selectivity for head‐to‐tail coupling observed for the corresponding acyclic pincer ligand.     

Reactivity and catalytic activity of a robust ruthenium(II)-triphos complex

The ruthenium(II)-triphos acetato complex [RuCl(OAc)(kappa3-triphos)] (triphos = (PPh2CH2)3CMe) has been found to be an active catalyst precursor for the hydrogenation of 1-alkenes under relatively mild conditions (5-50 bar H2, 50 degrees C). In contrast to related triphenylphosphine complexes, [RuCl(OAc)(kappa3-triphos)] is much less air sensitive and high catalytic activities were achieved when catalyst samples were prepared without exclusion of air or moisture. Substitution of the acetato ligand can be effected by treatment of acid, affording [Ru2(mu-Cl)3(kappa3-triphos)2]Cl and [RuCl(kappa3-triphos)]2(BF4)2 with aqueous HCl and [Et2OH]BF4, respectively, or by heating with dmpm in the presence of [NH4]PF6, resulting in formation of [RuCl(kappa2-dmpm)(kappa3-triphos)]PF6 (dmpm = PMe2CH2PMe2). A hydride complex, [RuHCl(kappa3-triphos)], formed by acetato-mediated heterolytic cleavage of dihydrogen is proposed as the active catalytic species. An inner-sphere, monohydride mechanism is suggested for the catalytic cycle, with chloro and triphos ligands playing a spectator role. These mechanistic proposals are consistent with reactivity studies carried out on [RuCl(OAc)(kappa3-triphos)] and [RuH(OAc)(kappa3-triphos)] and supported by a computational analysis. The solid-state structures of [RuCl(OAc)(kappa3-triphos)], [RuCl(kappa3-triphos)]2(BF4)2, and [RuCl(kappa2-dmpm)(kappa3-triphos)]PF6 have been established by X-ray diffraction.     

Electron irradiation at 0.5 MeV for copper single crystals

Results of isochronal anneals following electron irradiaton of copper single crystals indicate the I_B recovery is enhanced for a (100) sample compared to the I_B recovery for a (110) sample and a polycrystal sample. Comparison of these results with data from aluminum single crystals indicates a tentative assignment of the I_B defect in copper to damage produced in the (100) direction.     

C-C activation in the solid state in an organometallic σ-complex

Herein is reported the synthesis, by a solid-state reaction from [Ir(NBD)(2)(P(i)Pr(3))][BAr(F)(4)], of the first example of a C-C σ-complex with iridium, [Ir(BINOR-S)(P(i)Pr(3))][BAr(F)(4)]. This compound is unique in that in the solid state it undergoes reversible activation of the C-C single bond that interacts with the metal center, establishing a temperature-dependent equilibrium between Ir(III) C-C σ/Ir(V) bis-alkyl complexes. This process has been interrogated by variable-temperature X-ray diffraction, NMR spectroscopy, and DFT calculations.     

Aryl methyl sulfides as substrates for rhodium-catalyzed alkyne carbothiolation: arene functionalization with activating group recycling

A Rh(I)-catalyzed method for the efficient functionalization of arenes is reported. Aryl methyl sulfides are combined with terminal alkynes to deliver products of carbothiolation. The overall process results in reincorporation of the original arene functional group, a methyl sulfide, into the products as an alkenyl sulfide. The carbothiolation process can be combined with an initial Rh(I)-catalyzed alkene or alkyne hydroacylation reaction in three-component cascade sequences. The utility of the alkenyl sulfide products is also demonstrated in simple carbo- and heterocycle-forming processes. We also provide mechanistic evidence for the course of this new process.     

Activation energies in Gd using transient enhancement of the AC permeability

Analysis of the time delay of the transiently enhanced AC permeability of ferromagnetic Gd over the temperature range 240–290 K reveals a series of discrete, temperature dependent, time constants. These each follow a simple activation energy equation from which activation energies 0.62, 0.65 and 0.69 eV are resolved. These components are attributed to impurities for which significantly different diffusion rates were observed.     

The extraction of weak nuclear electric quadrupole splittings of dilute impurities in ferromagnets using modulated Adiabatic Passage NMR/ON

A novel extension of the Single or Adiabatic Fast Passage NMR/ON technique is described. Its principal advantages in extracting the mode magnitudes and distribution widths of weak nuclear electric quadrupole splittings much less than the magnetic inhomogeneous broadening are its simplicity and generality requiring no assumptions on the degree of adiabaticity of the nuclear spin motion during sweep through the quadrupolar split subresonances. The technique is applied to a concentrated single crystal sample of⁶⁰CoFe which failed to yield a well resolved mid passage signal to conventional single passage NMR/ON. The result is an asymmetric frequency distribution of quadrupole frequencies with a mode value of P=3e²qQ/4I (2I-1)=+4.5 ±1.0 kHz and half maxima of +2.5 kHz and +7.0 kHz.