Chiral Phosphoric Acid Catalyzed Atroposelective C−H Amination of Arenes

Abstract

N‐arylcarbazole structures are important because of their prevalence in natural products and functional OLED materials. C−H amination of arenes has been widely recognized as the most efficient approach to access these structures. Conventional strategies involving transition‐metal catalysts suffer from confined substrate generality and the requirement of exogenous oxidants. Organocatalytic enantioselective C–N chiral axis construction remains elusive. Presented here is the first organocatalytic strategy for the synthesis of novel axially chiral N‐arylcarbazole frameworks by the assembly of azonaphthalenes and carbazoles. This reaction accommodates broad substrate scope and gives atropisomeric N‐arylcarbazoles in good yields with excellent enantiocontrol. This approach not only offers an alternative to metal‐catalyzed C–N cross‐coupling, but also brings about opportunities for the exploitation of structurally diverse N‐aryl atropisomers and OLED materials.

Quantitative Analysis of the Multiple Roles Played by Halide Ions in Controlling the Growth Patterns of Palladium Nanocrystals

“…Although the methodology of seedmediated growth has been applied to many types of seeds, the growth of octahedral seeds enclosed by the thermodynamically stable {111} facets into other shapes has been very difficult to accomplish. Based on the previously reported experimental observations in the synthesis of Ag and Pd monometallic nanocrystals, [9,42,44] the growth would be automatically termi-nated as soon as an octahedral shape was attained. The atoms generated in the reaction solution would then undergo homogeneous nucleation to generate a second population of tiny nanoparticles.…”

“…Controlling the shapes and related properties of colloidal metal nanocrystals are critical to their vast applications in catalysis, photonics, electronics, sensing, and biomedicine. [1][2][3][4][5][6][7][8][9][10] Among the metals, Pd has attracted a great deal of attention and research efforts because of its fascinating performance in an array of catalytic reactions, such as Suzuki coupling, CO oxidation, alcohol oxidation, oxygen reduction, and selective hydrogenation. [11][12][13][14][15][16][17] Most of these applications prefer the use of Pd nanocrystals enclosed by a specific type of facet in order to optimize the activity and/or selectivity toward a reaction.…”

“…[11][12][13][14][15][16][17] Most of these applications prefer the use of Pd nanocrystals enclosed by a specific type of facet in order to optimize the activity and/or selectivity toward a reaction. [7][8][9][10] Thanks to the progress made by many research groups, Pd nanocrystals can now be synthesized with a variety of shapes and thus enclosed by distinctive facets through both thermodynamic and kinetic controls. [8] The most versatile approach to shape-controlled synthesis of Pd nanocrystals involves seedmediated growth, in which a salt precursor is introduced into a reaction mixture containing well-defined seeds.…”

“…[8] The most versatile approach to shape-controlled synthesis of Pd nanocrystals involves seedmediated growth, in which a salt precursor is introduced into a reaction mixture containing well-defined seeds. [9] Typical prod-ucts include cubes, cuboctahedra, octahedra, tetrahedral, rhombic dodecahedra, right bipyramids, decahedra, icosahedra, rectangular bars, pentagonal rods or wires, and thin plates, as well as those enclosed by high-index facets or concave surfaces.…”

“…[25] A similar mechanism has also been extended to control the shapes of Au, Ag, Pt, Ru, and Rh nanocrystals. [7][8][9][29][30][31] In general, the halide ions can i) affect the reduction potential of a salt precursor through the formation of PdX 4 2À (X=Cl À or Br À ), [18][19][20] ii) alter the order of surface free energies of different facets on the seed via chemisorption and thus change the relative growth rates of different facets, [21][22][23] and iii) induce localized oxidative etching on a specific facet of the seed to initiate anisotropic growth. [24][25][26][27][28] All these changes can impact the reduction kinetics and even reduction pathway of a precursor, enabling the formation of nanocrystals with diverse shapes.…”