Dynamics of Copper-Containing Porous Organic Framework Catalysts Reveal Catalytic Behavior Controlled by the Polymer Structure

Copper-Metallized Porous N-Heterocyclic Carbene Ligand Polymer-Catalyzed Regio- and Stereoselective 1,2-Carboboration of Alkynes

Alkenylboronates are highly versatile building blocks and valuable reagents in the synthesis of complex molecules. Compared with that of monosubstituted alkenylboronates, the synthesis of multisubstituted alkenylboronates is challenging. The copper-catalyzed carboboration of alkynes is an operationally simple and straightforward method for synthesizing bis/trisubstituted alkenylboronates. In this work, a series of copper-metallized N-Heterocyclic Carbene (NHC) ligand porous polymer catalysts are designed and synthesized in accordance with the mechanism of carboboration. By using CuCl@POL-NHC-Ph as the optimal nanocatalyst, this study realizes the β-regio- and stereoselective (syn-addition) 1,2-carboboration of alkynes (regioselectivity up to >99:1) with satisfactory yields and a wide range of substrates. This work not only overcomes the selectivity of carboboration but also provides a new strategy for the design of nanocatalysts and their application in organic synthesis.

Accessibility and Mechanical Stability of Nanoporous Zinc Oxide and Aluminum Oxide Coatings Synthesized via Infiltration of Polymer Templates

The conformal nanoporous inorganic coatings with accessible pores that are stable under applied thermal and mechanical stresses represent an important class of materials used in the design of sensors, optical coatings, and biomedical systems. Here, we synthesize porous AlOx and ZnO coatings by the sequential infiltration synthesis (SIS) of two types of polymers that enable the design of porous conformal coatings-polymers of intrinsic microporosity (PIM) and block co-polymer (BCP) templates. Using quartz crystal microbalance (QCM), we show that alumina precursors infiltrate both polymer templates four times more efficiently than zinc oxide precursors. Using the quartz crystal microbalance (QCM) technique, we provide a comprehensive study on the room temperature accessibility to water and ethanol of pores in block copolymers (BCPs) and porous polymer templates using polystyrene-block-poly-4-vinyl pyridine (PS75-b-P4VP25) and polymers of intrinsic microporosity (PIM-1), polymer templates modified by swelling, and porous inorganic coatings such as AlOx and ZnO synthesized by SIS using such templates. Importantly, we demonstrate that no structural damage occurs in inorganic nanoporous AlOx and ZnO coatings synthesized via infiltration of the polymer templates during the water freezing/melting cycling tests, suggesting excellent mechanical stability of the coatings, even though the hardness of the inorganic nanoporous coating is affected by the polymer and precursor selections. We show that the hardness of the coatings is further improved by their annealing at 900 °C for 1 h, though for all the cases except ZnO obtained using the BCP template, this annealing has a negligible effect on the porosity of the material, as is confirmed by the consistency in the optical characteristics. These findings unravel new potential for the materials being used across various environment and temperature conditions.

Ambient synthesis of metal-covalent organic frameworks with Fe-iminopyridine linkages

Highly crystalline Fe-COFs were constructed from the building blocks carrying pyridyl-aldehyde and triamine moieties in the presence of Fe(OTf)₂ and acetic acid under ambient conditions via a subcomponent assembly strategy. The spectral results prove the coordination of atomically distributed Fe(II) ions with the nitrogen species of covalently formed iminopyridine linkages.

Design of Organic/Inorganic Hybrid Catalysts for Energy and Environmental Applications

Controlling selectivity between competing reaction pathways is crucial in catalysis. Several approaches have been proposed to achieve this goal in traditional heterogeneous catalysts including tuning nanoparticle size, varying alloy composition, and controlling supporting material. A less explored and promising research area to control reaction selectivity is via the use of hybrid organic/inorganic catalysts. These materials contain inorganic components which serve as sites for chemical reactions and organic components which either provide diffusional control or directly participate in the formation of active site motifs. Despite the appealing potential of these hybrid materials to increase reaction selectivity, there are significant challenges to the rational design of such hybrid nanostructures. Structural and mechanistic characterization of these materials play a key role in understanding and, therefore, designing these organic/inorganic hybrid catalysts. This Outlook highlights the design of hybrid organic/inorganic catalysts with a brief overview of four different classes of materials and discusses the practical catalytic properties and opportunities emerging from such designs in the area of energy and environmental transformations. Key structural and mechanistic characterization studies are identified to provide fundamental insight into the atomic structure and catalytic behavior of hybrid organic/inorganic catalysts. Exemplary works are used to show how specific active site motifs allow for remarkable changes in the reaction selectivity. Finally, to demonstrate the potential of hybrid catalyst materials, we suggest a characterization-based approach toward the design of biomimetic hybrid organic/inorganic materials for a specific application in the energy and environmental research space: the conversion of methane into methanol.