Formation,Expansion, and Interconversion of Metallarings in a Sulfur‐Bridged AuICoIII Coordination System

A novel Au^ICo^III coordination system that is derived from the newly prepared [Co(D ‐nmp)₂]⁻ ( 1 ⁻; D ‐nmp=N‐methyl‐D ‐penicillaminate) and a gold(I) precursor Au^I is reported. Complex 1 ⁻ acts as a sulfur‐donating metallaligand and reacts with the gold(I) precursor to give [Au₂Co₂(D ‐nmp)₄] ( 2 ), which has an eight‐membered Au^I₂Co^III₂ metallaring. Treatment of 2 with [Au₂(dppe)₂]²⁺ (dppe=1,2‐bis(diphenylphosphino)ethane) leads to the formation of [Au₄Co₂(dppe)₂(D ‐nmp)₄]²⁺ ( 3 ²⁺), which consists of an 18‐membered Au^I₄Co^III₂ metallaring that accommodates a tetrahedral anion (BF₄⁻, ClO₄⁻, ReO₄⁻). In solution, the metallaring structure of 3 ²⁺ is readily interconvertible with the nine‐membered Au^I₂Co^III metallaring structure of [Au₂Co(dppe)(D ‐nmp)₂]⁺ ( 4 ⁺); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the Au S and Au P bonds, which is essential for metallaring expansion and contraction.     

Production of Alkyl Aryl Sulfides from Aromatic Disulfides and Alkyl Carboxylates via a Disilathiane–Disulfide Interchange Reaction

The results of this study show that disilathiane is an effective mediator in the synthesis of alkyl aryl sulfides with disulfides and alkyl carboxylates. Mechanistic studies suggest that disilathiane promotes cleavage of the sulfur–sulfur bond of disulfides to generate thiosilane as a key intermediate. Diselenides were also applicable to this transformation to produce the corresponding selenides.     

Isotopic dependence of the giant monopole resonance in the even-A 112-124Sn isotopes and the asymmetry term in nuclear incompressibility

The strength distributions of the giant monopole resonance (GMR) have been measured in the even-A Sn isotopes (A=112-124) with inelastic scattering of 400-MeV alpha particles in the angular range 0 degrees -8.5 degrees . We find that the experimentally observed GMR energies of the Sn isotopes are lower than the values predicted by theoretical calculations that reproduce the GMR energies in 208Pb and 90Zr very well. From the GMR data, a value of Ktau = -550 +/- 100 MeV is obtained for the asymmetry term in the nuclear incompressibility.     

Gamow-Teller strength in the exotic odd-odd nuclei 138La and 180Ta and its relevance for neutrino nucleosynthesis

The Gamow-Teller strength distributions below the particle threshold in 138La and 180Ta, deduced from high-resolution measurements of the (3He,t) reaction at 0 degrees, allow us to evaluate the role of charged-current reactions for the production of these extremely rare nuclides in neutrino-nucleosynthesis models. The analysis suggests that essentially all 138La in the Universe can be made that way. Neutrino nucleosynthesis also contributes significantly to the abundance of 180Ta but the magnitude depends on the unknown branching ratio for population of the long-lived isomer.     

Palladium–N‐Heterocyclic Carbene (NHC)‐Catalyzed Asymmetric Synthesis of Indolines through Regiodivergent C(sp3)H Activation: Scope and DFT Study

Two bulky, chiral, monodentate N‐heterocyclic carbene ligands were applied to palladium‐catalyzed asymmetric C?H arylation to incorporate C(sp³)?H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans‐2,3‐substituted indolines. Although this C_Ar?C_alkyl coupling requires high temperatures (140–160 °C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The C?H activation at a tertiary center was realized only in the case of a cyclopropyl group. No C?H activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine C?H activation is used to rationalize experimentally observed regio‐ and enantioselectivities.     

Well‐Defined Iron Complexes as Efficient Catalysts for “Green” Atom‐Transfer Radical Polymerization of Styrene,Methyl Methacrylate,and Butyl Acrylate with Low Catalyst Loadings and Catalyst Recycling

Environmentally friendly iron(II) catalysts for atom‐transfer radical polymerization (ATRP) were synthesized by careful selection of the nitrogen substituents of N,N,N‐trialkylated‐1,4,9‐triazacyclononane (R₃TACN) ligands. Two types of structures were confirmed by crystallography: “[(R₃TACN)FeX₂]” complexes with relatively small R groups have ionic and dinuclear structures including a [(R₃TACN)Fe(μ‐X)₃Fe(R₃TACN)]⁺ moiety, whereas those with more bulky R groups are neutral and mononuclear. The twelve [(R₃TACN)FeX₂]_n complexes that were synthesized were subjected to bulk ATRP of styrene, methyl methacrylate (MMA), and butyl acrylate (BA). Among the iron complexes examined, [{(cyclopentyl)₃TACN}FeBr₂] ( 4 b ) was the best catalyst for the well‐controlled ATRP of all three monomers. This species allowed easy catalyst separation and recycling, a lowering of the catalyst concentration needed for the reaction, and the absence of additional reducing reagents. The lowest catalyst loading was accomplished in the ATRP of MMA with 4 b (59 ppm of Fe based on the charged monomer). Catalyst recycling in ATRP with low catalyst loadings was also successful. The ATRP of styrene with 4 b (117 ppm Fe atom) was followed by precipitation from methanol to give polystyrene that contained residual iron below the calculated detection limit (0.28 ppm). Mechanisms that involve equilibria between the multinuclear and mononuclear species were also examined.     

Dynamic and static nature of activated interactions in transition states as elucidated by quantum theory of atoms-in-molecules dual functional analysis: A case of ligand exchange at the N of sulfonylimino-λ3-bromanes

A method to elucidate the dynamic and static natures of the activated interactions in transition states (TSs) is proposed using quantum theory of atoms-in-molecules (QTAIM) dual functional analysis (QTAIM-DFA). The natures are determined for the ligand exchange at the N of sulfonylimino-λ³-bromanes, RBr-*-N(SO₂CF₃)-*-X′R′ (R, R′ = Me or Ph, X′ = Br′ or I′). Asterisks (*) emphasize the presence of bond critical points within the interactions in question. While data from the optimized structures of TSs correspond to the static nature, those from the perturbed and optimized structures represent the dynamic nature. The nature of the interactions in Br-*-N-*-X′ calculated with QTAIM-DFA, using the perturbed structures generated using the normal coordinates for the imaginary frequencies (NIV), was very similar to that in trigonal bipyramidal adduct formation through charge transfer. The results with NIV were precisely the same as those obtained based on intrinsic reaction coordinate (IRC). The high applicability of QTAIM-DFA is demonstrated when analyzing the activated interactions in TSs.     

Silaboration of [1.1.1]Propellane: A Storable Feedstock for Bicyclo[1.1.1]pentane Derivatives

The silaboration of [1.1.1]propellane enables direct introduction of B and Si functional groups onto the bicyclo[1.1.1]pentane (BCP) scaffold in high yield under mild, additive‐free conditions. The silaborated BCP can be obtained on a gram‐scale in a single step without the need for column‐chromatographic purification, and is storable and easy to handle, providing a versatile synthetic intermediate for BCP derivatives. We also describe various conversions of the C?B/C?Si bonds on the BCP scaffold, including development of a modified Suzuki–Miyaura cross‐coupling reaction at the highly sterically hindered bridgehead sp³ carbon center of the BCP skeleton using a combination of highly activated BCP boronic esters, copper(I) oxide, and a PdCl₂(dppf) catalyst system.