Triphenylphosphine-Functionalized Core-Cross-Linked Micelles and Nanogels with a Polycationic Outer Shell: Synthesis and Application in Rhodium-Catalyzed Biphasic Hydrogenations

Unimolecular amphiphilic nanoreactors with a poly(4-vinyl-N-methylpyridinium iodide) (P4VPMe⁺I⁻) polycationic outer shell and two different architectures (core-cross-linked micelles, CCM, and nanogels, NG), with narrow size distributions around 130–150 nm in diameter, were synthesized by RAFT polymerization from an R₀-4VPMe⁺I⁻₁₄₀-b-S₅₀-SC(S)SPr macroRAFT agent by either chain extension with a long (300 monomer units) hydrophobic polystyrene-based block followed by cross-linking with diethylene glycol dimethacrylate (DEGDMA) for the CCM particles, or by simultaneous chain extension and cross-linking for the NG particles. A core-anchored triphenylphosphine (TPP) ligand functionality was introduced by using 4-diphenylphosphinostyrene (DPPS) as a comonomer (5–20 % mol mol⁻¹) in the chain extension (for CCM) or chain extension/cross-linking (for NG) step. The products were directly obtained as stable colloidal dispersions in water (latexes). After loading with [RhCl(COD)]₂ to yield [RhCl(COD)(TPP@CCM)] or [RhCl(COD)(TPP@NG)], respectively, the polymers were used as polymeric nanoreactors in Rh-catalyzed aqueous biphasic hydrogenation of the model substrates styrene and 1-octene, either neat (for styrene) or in an organic solvent (toluene or 1-nonanol). All hydrogenations were rapid (TOF up to 300 h⁻¹) at 25 °C and 20 bar of H₂ pressure, the biphasic mixture rapidly decanted at the end of the reaction (<2 min), the Rh loss was negligible (<0.1 ppm in the recovered organic phase), and the catalyst phase could be recycled 10 times without significant loss of catalytic activity.     

Dormant versus Evolving Aminopalladated Intermediates: Toward a Unified Mechanistic Scenario in PdII‐Catalyzed Aminations

Pd^II‐catalyzed alkene aminopalladation and allylic C?H activation are two competing reaction sequences sharing the same reaction conditions. This study aimed at understanding the factors that bias one or the other path in the intramolecular oxidative cyclization of two types of N‐tosyl amidoalkenes. The results obtained are in accord with the initial generation of a high‐energy cyclic (5‐ or 6‐membered) aminopalladated intermediate. However, this latter species can evolve only if the following specific conditions are met: the availability of distocyclic β‐H elimination pathway, the presence of a strong terminal oxidant, or the availability of a carbopalladation pathway. Conversely, the cyclic alkylpalladium complex is only a latent species in equilibrium with the initial substrate and cannot evolve. Such a reactivity hurdle leaves the way open for alternative reactivities such as allylic C?H activation of the olefinic substrate to generate a η³‐allyl complex followed by its interception by the nitrogen nucleophile, [3,3]‐sigmatropic rearrangement, or decomposition. This study proposes a unifying mechanistic picture that connects these competing mechanisms.     

E2 polarization charge in Sn

The nucleus ¹⁰²Sn, which is the lightest Sn isotope with known excited states, was investigated with the ⁵⁰Cr(⁵⁸Ni,α2n) reaction using delayed in-beam γ-ray and conversion-electron spectroscopy. The experimental setup was designed to study the decay of μs-long isomeric states by placing γ-ray and electron detectors behind the focal plane of the Fragment Mass Analyzer at the Argonne National Laboratory. A 44 keV conversion-electron line corresponding to the (6⁺)→(4⁺) transition in ¹⁰²Sn was identified and a half-life of 0.62^+0.43_−0.19 μs was measured for the (6⁺) state. From the available experimental information neutron effective charges from 1.6 to 2.3 e were deduced, based on the comparison with different shell-model calculations.     

High spin states in48Cr

The self-consistent finite Fermi-system theory with three different parameter sets is used to calculate decay energies and Gamow-Teller strength distributions of neutronrich short-lived nuclides near shell closures Z=50, N=82. Among the parameters, the role of a strong surface neutron-proton attraction and an isovector spin-orbit force is discussed. The obtainedβ-decay half-lives are compared with large-scale calculation results and with available experimental data. Some predictions for the ground state properties of other unstable closed-shell nuclei are presented.     

A study of γ decays and octupole bands in 21Ne and 21Na

The reactions ¹⁶O(⁷Li, 2n) and ¹⁶O(⁷Li, np) populating ²¹Na and ²¹Ne have been studied at E _L=27 MeV using the GASP γ-detector array. The level schemes for ²¹Na and ²¹Ne have been extended to higher spin. The population of the bands with K=3/2 and 1/2, forming parity doublets, are compared. Preferential E1 decay between bands of opposite parity is observed in agreement with the octupole scenario. The structure of these bands can be interpreted as consisting of an instrinsic asymmetric (⁴He + ¹⁶O) structure with octupole deformation.