Colloidal Atomic Layer Deposition on Nanocrystals Using Ligand-Modified Precursors.

Atomic layer deposition (ALD) is a method to grow thin metal oxide layers on a variety of materials for applications spanning from electronics to catalysis. Extending ALD to colloidally stable nanocrystals promises to combine the benefits of thin metal oxide coatings with the solution processability of the nanocrystals. However, challenges persist in applying this method, which relate to finding precursors that promote the growth of the metal oxide while preserving colloidal stability throughout the process. Herein, we introduce a colloidal ALD method to coat nanocrystals with amorphous metal oxide shells using metal and oxygen precursors that act as colloidal stabilizing ligands. Our scheme involves metal-amide precursors modified with solubilizing groups and oleic acid as the oxygen source. The growth of the oxide is self-limiting and proceeds in a layer-by-layer fashion. Our protocol is generalizable and intrinsically scalable. Potential applications in display, light detection, and catalysis are envisioned.

Voltage-Driven Chemical Reactions Enable the Synthesis of Tunable Liquid Ga-Metal Nanoparticles.

Nanosized particles of liquid metals are emerging materials that hold promise for applications spanning from microelectronics to catalysis. Yet, knowledge of their chemical reactivity is largely unknown. Here, we study the reactivity of liquid Ga and Cu nanoparticles under the application of a cathodic voltage. We discover that the applied voltage and the spatial proximity of these two particle precursors dictate the reaction outcome. In particular, we find that a gradual voltage ramp is crucial to reduce the native oxide skin of gallium and enable reactive wetting between the Ga and Cu nanoparticles; instead, a voltage step causes dewetting between the two. We determine that the use of liquid Ga/Cu nanodimer precursors, which consist of an oxide-covered Ga domain interfaced with a metallic Cu domain, provides a more uniform mixing and results in more homogeneous reaction products compared to a physical mixture of Ga and Cu NPs. Having learned this, we obtain CuGa2 alloys or solid@liquid CuGa2@Ga core@shell nanoparticles by tuning the stoichiometry of Ga and Cu in the nanodimer precursors. These products reveal an interesting complementarity of thermal and voltage-driven syntheses to expand the compositional range of bimetallic NPs. Finally, we extend the voltage-driven synthesis to the combination of Ga with other elements (Ag, Sn, Co, and W). By rationalizing the impact of the native skin reduction rate, the wetting properties, and the chemical reactivity between Ga and other metals on the results of such voltage-driven chemical manipulation, we define the criteria to predict the outcome of this reaction and set the ground for future studies targeting various applications for multielement nanomaterials based on liquid Ga.

Copper-catalyzed oxidative benzylic C(sp3)-H amination: direct synthesis of benzylic carbamates.

A new efficient strategy to access benzylic carbamates through C-H activation is reported. The use of a catalytic amount of a Cu(i)/diimine ligand in combination with NFSI ((PhSO2)2NF) or F-TEDA-PF6 as oxidants and H2NCO2R as an amine source directly leads to the C-N bond formation at the benzylic position. The mild reaction conditions and the broad substrate scope make this transformation a useful method for the late-stage incorporation of a ubiquitous carbamate fragment onto hydrocarbons.