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

Iron-Catalyzed [2 + 2 + 2] Cycloaddition Reactions of Diynes with Oxyphosphaethynes To Construct 2‑Phosphaphenol Derivatives

Iron-catalyzed [2 + 2 + 2] cycloaddition reactions of diynes with siloxyphosphaethynes have been developed to give 2-phosphaphenol derivatives. The use of electronically neutral siloxyphosphaethynes generated in situ by the reaction of anionic phosphaethynolate with silyl triflates is key to achieving the reactions

Cooperative Catalytic Reactions Using Organocatalysts and Transition Metal Catalysts: Propargylic Allylation of Propargylic Alcohols with α,β-Unsaturated Aldehydes

Propargylic allylation of propargylic alcohols with α,β-unsaturated aldehydes in the presence of a thiolate-bridged diruthenium complex and a secondary amine as cocatalysts has been found to give the corresponding propargylic allylated products, where the γ-propargylation occurs selectively at the α,β-unsaturated aldehydes, in high yields as a mixture of two diastereoisomers

Visible-Light-Mediated Utilization of α-Aminoalkyl Radicals: Addition to Electron-Deficient Alkenes Using Photoredox Catalysts

Synthetic use of α-aminoalkyl radicals formed by single electron oxidation of amines is quite limited. Here we demonstrate addition of α-aminoalkyl radicals to electron-deficient alkenes by visible-light-mediated electron transfer using transition metal polypyridyl complexes as photocatalysts, via a sequential redox pathway

Copper-Catalyzed Enantioselective Propargylic Etherification of Propargylic Esters with Alcohols

Enantioselective propargylic etherification of propargylic esters with not only aliphatic alcohols but also phenols in the presence of a catalytic amount of copper-Pybox complex gives the corresponding propargylic ethers in good to high yields with a high to excellent enantioselectivity (up to 99% ee). The result described here provides the first successful example of enantioselective propargylic etherificatio

Hydroboration of Alkynes Catalyzed by Pyrrolide-Based PNP Pincer–Iron Complexes

To utilize iron complexes as catalysts, the application of a well-designed ligand is critical to control the reactivity of the iron center. Recently, our group has succeeded in the synthesis of iron complexes bearing a pyrrolide-based PNP pincer ligand and their application to the catalytic transformation of dinitrogen into ammonia under mild reaction conditions. As an extensive study, we report the iron-catalyzed hydroboration of alkynes with pinacolborane, where the corresponding <i>E</i>-isomers are obtained selectively

Synthesis, Structure, and Reactivity of Group VI Metal Complexes Bearing Group IV Metallocenyldiphosphine Moieties and a Pentamethylcyclopentadienyl Ligand

A series of group VI metal complexes bearing a group IV metallocenyldiphosphine moiety and a pentamethylcyclopentadienyl ligand have been prepared and structurally characterized. Reactions of trinuclear complexes with KC₈ give the corresponding neutral chloride-bridged complexes. Further reaction of the resulting chloride-bridged complex with NaBAr^F₄ gives the corresponding monocationic chloride-bridged complex. On the other hand, reactions of the neutral chloride-bridged complexes with <i>n</i>-BuLi give the corresponding chloride-bridged alkyl complexes, where the group IV metallocene­(III) moiety and the coordinatively unsaturated group VI metal­(II) center are in close proximity. Spectroscopic and crystallographic studies of the reaction of a chloride-bridged alkyl complex with CO or a protic acid indicate that further disproportionation takes place at the alkyl zirconocene­(III) moiety

Ruthenium- and Copper-Catalyzed Enantioselective Propargylic Alkylation of Propargylic Alcohols with β-Keto Phosphonates

The enantioselective propargylic alkylation of propargylic alcohols with β-keto phosphonates in the presence of a thiolate-bridged diruthenium complex and a copper complex as cocatalysts gives the corresponding propargylic alkylated products in excellent yields with high diastereo- and enantioselectivities (up to 97% ee)

Synthesis and Reactivity of Hybrid Phosphido- and Hydrosulfido-Bridged Diruthenium Complexes: Transformations into Diruthenium and Tetraruthenium Complexes Bridged by Phosphido and Sulfido Ligands

The reaction of the monophosphido-bridged diruthenium­(III) complex [Cp*RuCl­(μ-PMe₂)­(μ-Cl)­RuClCp*] with sodium hydrogen sulfide affords the hybrid phosphido- and hydrosulfido-bridged diruthenium­(III) complex [Cp*RuCl­(μ-PMe₂)­(μ-SH)­RuClCp*]. The hydrosulfido-bridged diruthenium­(III) complex can be further converted into the corresponding sulfido-bridged multinuclear ruthenium­(III) complex via deprotonation of the hydrosulfido ligand. The hydrosulfido-bridged diruthenium­(III) complex also reacts with bases to afford a coordinatively unsaturated diruthenium­(III) complex, where insertion of terminal alkynes further occurs to form phosphido-bridged diruthenium­(III) complexes bearing ruthenathiacyclobutene moieties

Synthesis, Structure, and Reactivity of Group VI Metal Complexes Bearing Group IV Metallocenyldiphosphine Moieties and a Pentamethylcyclopentadienyl Ligand

A series of group VI metal complexes bearing a group IV metallocenyldiphosphine moiety and a pentamethylcyclopentadienyl ligand have been prepared and structurally characterized. Reactions of trinuclear complexes with KC₈ give the corresponding neutral chloride-bridged complexes. Further reaction of the resulting chloride-bridged complex with NaBAr^F₄ gives the corresponding monocationic chloride-bridged complex. On the other hand, reactions of the neutral chloride-bridged complexes with <i>n</i>-BuLi give the corresponding chloride-bridged alkyl complexes, where the group IV metallocene­(III) moiety and the coordinatively unsaturated group VI metal­(II) center are in close proximity. Spectroscopic and crystallographic studies of the reaction of a chloride-bridged alkyl complex with CO or a protic acid indicate that further disproportionation takes place at the alkyl zirconocene­(III) moiety