Chiral bipyridines represent a class of ligands noted for their distinctive reactivity and stereoselectivity in metal-catalyzed reactions.Herein,we have developed a new class of bifunctional C_(2)-symmetric chiral bip...Chiral bipyridines represent a class of ligands noted for their distinctive reactivity and stereoselectivity in metal-catalyzed reactions.Herein,we have developed a new class of bifunctional C_(2)-symmetric chiral bipyridine-type tetradentate ligands,abbreviated as Bpy-Bisulidines.These crab-shape ligands feature that:(1)bipyridine framework possesses the rich coordination ability with various metal ions;(2)chiral imidazolidine could generate a deep chiral pocket;(3)C_(2)-symmetry could reduce the number of possible transition states;(4)rigid chiral enviroments are close to the metal,and(5)imidazolidine N-H moiety acts as hydrogen-bonding donor.The newly developed chiral Bpy-Bisulidine ligands were successfully applied in Ni(II)-catalyzed asymmetric Friedel-Crafts alkylation reaction and inverse-electron-demand Hetero-Diels-Alder reactions,achieving excellent stereoselectivities.Our work is the first example of bifunctional C_(2)-symmetric chiral imidazolidine-type tetradentate ligands.X-ray crystallographic analysis of the Bpy-Bisulidine-Ni(OTf)_(2)complex,control experiments and linear correlation showed that the catalytically active species was a monomeric catalyst.展开更多
This article presents a compact crab-shaped reconfigurable antenna(CSRA)designed for 5G sub-6 GHz wireless applications. The antenna achieves enhanced gain in a miniaturized form factor by incorporating a hexagonal sp...This article presents a compact crab-shaped reconfigurable antenna(CSRA)designed for 5G sub-6 GHz wireless applications. The antenna achieves enhanced gain in a miniaturized form factor by incorporating a hexagonal split-ring structure controlled via two radio frequency(RF) positive-intrinsicnegative(PIN) diodes(BAR64-02V). While the antenna is primarily designed to operate at 3.50 GHz for sub-6 GHz 5G applications, RF switching enables the CSRA to cover a broader frequency spectrum, including the S-band, X-band, and portions of the Ku-band. The proposed antenna offers several advantages: It is low-cost(fabricated on an FR-4 substrate), compact(achieving 64.07% size reduction compared to conventional designs), and features both frequency and gain reconfigurability through digitally controlled PIN diode switching. The reflection coefficients of the antenna, both without diodes and across all four switching states, were experimentally validated in the laboratory using a Keysight Field Fox microwave analyzer(N9916A, 14 GHz). The simulated radiation patterns and gain characteristics closely matched the measured values, demonstrating an excellent agreement. This study bridges the gap between traditional and next-generation antenna designs by offering a compact,cost-effective, and high-performance solution for multiband, reconfigurable wireless communication systems. The integration of double-split-ring resonators and dynamic reconfigurability makes the proposed antenna a strong candidate for various applications, including S-band and X-band systems, as well as the emerging lower 6G band(7.125 GHz–8.400 GHz).展开更多
基金the financial support from the NSFC(22361009)Guizhou Provincial Basic Research Program(GCC[2023]078,ZK[2023]043,ZK[2024]374).
文摘Chiral bipyridines represent a class of ligands noted for their distinctive reactivity and stereoselectivity in metal-catalyzed reactions.Herein,we have developed a new class of bifunctional C_(2)-symmetric chiral bipyridine-type tetradentate ligands,abbreviated as Bpy-Bisulidines.These crab-shape ligands feature that:(1)bipyridine framework possesses the rich coordination ability with various metal ions;(2)chiral imidazolidine could generate a deep chiral pocket;(3)C_(2)-symmetry could reduce the number of possible transition states;(4)rigid chiral enviroments are close to the metal,and(5)imidazolidine N-H moiety acts as hydrogen-bonding donor.The newly developed chiral Bpy-Bisulidine ligands were successfully applied in Ni(II)-catalyzed asymmetric Friedel-Crafts alkylation reaction and inverse-electron-demand Hetero-Diels-Alder reactions,achieving excellent stereoselectivities.Our work is the first example of bifunctional C_(2)-symmetric chiral imidazolidine-type tetradentate ligands.X-ray crystallographic analysis of the Bpy-Bisulidine-Ni(OTf)_(2)complex,control experiments and linear correlation showed that the catalytically active species was a monomeric catalyst.
文摘This article presents a compact crab-shaped reconfigurable antenna(CSRA)designed for 5G sub-6 GHz wireless applications. The antenna achieves enhanced gain in a miniaturized form factor by incorporating a hexagonal split-ring structure controlled via two radio frequency(RF) positive-intrinsicnegative(PIN) diodes(BAR64-02V). While the antenna is primarily designed to operate at 3.50 GHz for sub-6 GHz 5G applications, RF switching enables the CSRA to cover a broader frequency spectrum, including the S-band, X-band, and portions of the Ku-band. The proposed antenna offers several advantages: It is low-cost(fabricated on an FR-4 substrate), compact(achieving 64.07% size reduction compared to conventional designs), and features both frequency and gain reconfigurability through digitally controlled PIN diode switching. The reflection coefficients of the antenna, both without diodes and across all four switching states, were experimentally validated in the laboratory using a Keysight Field Fox microwave analyzer(N9916A, 14 GHz). The simulated radiation patterns and gain characteristics closely matched the measured values, demonstrating an excellent agreement. This study bridges the gap between traditional and next-generation antenna designs by offering a compact,cost-effective, and high-performance solution for multiband, reconfigurable wireless communication systems. The integration of double-split-ring resonators and dynamic reconfigurability makes the proposed antenna a strong candidate for various applications, including S-band and X-band systems, as well as the emerging lower 6G band(7.125 GHz–8.400 GHz).
