Gravitational fermion creation during an anisotropic phase of cosmological expansion

The free Dirac equation is solved in a Bianchi Type I space-time, which represents a homogeneous but anisotropic universe, to show the creation of fermionic particles. It is found that unlike in the isotropic case, massless fermion production is possible. An estimate of the energy density of massless particles created during an early anisotropic phase of cosmological expansion is shown to cause substantial back-reaction on the gravitational field. The potential relevance to dark matter particle production, primordial magnetogenesis, and early universe cosmology is discussed briefly.Comment: Accepted for publication in Physical Review

Acceptorless Dehydrogenation of C–C Single Bonds Adjacent to Functional Groups by Metal–Ligand Cooperation

Unprecedented direct acceptorless dehydrogenation of C–C single bonds adjacent to functional groups to form α,β-unsaturated compounds has been accomplished by using a new class of group 9 metal complexes. Metal–ligand cooperation operated by the hydroxycyclopentadienyl ligand was proposed to play a major role in the catalytic transformation

Dehydrogenation of Dimethylamine–Borane Catalyzed by Half-Sandwich Ir and Rh Complexes: Mechanism and the Role of Cp* Noninnocence

Half-sandwich Cp*Rh^III complexes (Cp* = η⁵-1,2,3,4,5-pentamethylcyclopentadienyl) supported by 2,2′-bipyridine or 4,4′-di-<i>tert</i>-butyl-2,2′-bipyridine catalyze dehydrogenation of dimethylamine–borane (Me₂NH·BH₃) to produce H₂ and dimethylamino–borane dimer (Me₂NBH₂)₂ with turnovers of 2200. The Ir^III analogues, on the other hand, display dramatically poorer catalytic activity. Mechanistic inferences drawn from stoichiometric reactions and DFT calculations suggest noninnocent involvement of the Cp* moiety as a proton shuttle

Acceptorless Dehydrogenation of C–C Single Bonds Adjacent to Functional Groups by Metal–Ligand Cooperation

Unprecedented direct acceptorless dehydrogenation of C–C single bonds adjacent to functional groups to form α,β-unsaturated compounds has been accomplished by using a new class of group 9 metal complexes. Metal–ligand cooperation operated by the hydroxycyclopentadienyl ligand was proposed to play a major role in the catalytic transformation

Dehydrogenation of Dimethylamine–Borane Catalyzed by Half-Sandwich Ir and Rh Complexes: Mechanism and the Role of Cp* Noninnocence

Half-sandwich Cp*Rh^III complexes (Cp* = η⁵-1,2,3,4,5-pentamethylcyclopentadienyl) supported by 2,2′-bipyridine or 4,4′-di-<i>tert</i>-butyl-2,2′-bipyridine catalyze dehydrogenation of dimethylamine–borane (Me₂NH·BH₃) to produce H₂ and dimethylamino–borane dimer (Me₂NBH₂)₂ with turnovers of 2200. The Ir^III analogues, on the other hand, display dramatically poorer catalytic activity. Mechanistic inferences drawn from stoichiometric reactions and DFT calculations suggest noninnocent involvement of the Cp* moiety as a proton shuttle

Facile Styrene Formation from Ethylene and a Phenylplatinum(II) Complex Leading to an Observable Platinum(II) Hydride

A new 2-(di-<i>tert</i>-butylphosphanyl)­benzenesulfonate-supported phenylplatinum­(II) complex instantaneously but reversibly binds ethylene at room temperature. Direct and rapid styrene formation at room temperature via insertion of the Pt^II-bound ethylene into the Pt^II–Ph fragment followed by β-hydride elimination results in the formation of a solution-stable Pt^II–H complex. The Pt^II–H fragment is resistant toward protonolysis by acetic acid. Oxidation of the Pt^II–H fragment by excess Cu^II(OTf)₂ leads to an inorganic Pt^II complex incapable of C–H activation

Cp*Ir-Catalyzed Acceptorless Dehydrogenation of Carbon–Carbon Single Bonds

Pentamethylcyclopentadienyl (Cp*) iridium­(III) chloride catalyzed acceptorless dehydrogenation of α-tetralone is reported. Cp* iridium chloride showed higher activity in comparison to other Cp* iridium complexes having bromide, iodide, or hydride or complexes without a Cp ring. The desired product, naphthol, was obtained in up to 71% yield from α-tetralone. The dehydrogenation by Cp* iridium catalyst could be applied to not only α-tetralone but also dihydrocoumarin, dihydroquinolinone, dimethylcyclohexanone, dihydrobenzofuran and 1-isochromanone, although the conversion stayed moderate. The catalytic turnover was not limited by the increased concentration of the product but by catalyst decomposition

Correction to Why Did Incorporation of Acrylonitrile to a Linear Polyethylene Become Possible? Comparison of Phosphine–Sulfonate Ligand with Diphosphine and Imine–Phenolate Ligands in the Pd-Catalyzed Ethylene/Acrylonitrile Copolymerization

Correction to Why Did Incorporation of Acrylonitrile to a Linear Polyethylene Become Possible? Comparison of Phosphine–Sulfonate Ligand with Diphosphine and Imine–Phenolate Ligands in the Pd-Catalyzed Ethylene/Acrylonitrile Copolymerizatio