Porous Salts as Platforms for Heterogeneous Catalysis

Area of Science:

• Materials Science
• Inorganic Chemistry
• Coordination Chemistry

Background:

• Porous coordination cages offer unique structural properties for hosting guest molecules or ions.
• Metal-organic frameworks (MOFs) and related porous materials are actively researched for catalysis and gas storage.
• Stabilizing reactive metal centers in a solid-state environment is crucial for developing heterogeneous catalysts.

Purpose of the Study:

• To synthesize a novel class of reactive porous solids.
• To immobilize and stabilize reactive chromium(II) centers within a porous solid matrix.
• To investigate the accessibility, stability, and reactivity of the immobilized chromium centers.

Main Methods:

• Salt metathesis reactions between a magnesium-based porous coordination cage and a chromium(II) salt.
• Characterization using UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), ion chromatography (IC), and inductively coupled plasma mass spectrometry (ICP-MS).
• Analysis of porosity using Brunauer-Emmett-Teller (BET) surface area measurements.
• Structural determination via single crystal X-ray diffraction.

Main Results:

• A new porous solid was successfully prepared via salt metathesis, incorporating chromium(II) ions.
• The material exhibited a BET surface area of 213 m² g⁻¹.
• Single crystal X-ray diffraction confirmed chromium(II) cations located in the interstitial spaces between porous cages.
• UV-vis spectroscopy indicated that the chromium(II) centers remained accessible and reactive in the solid state.
• The immobilized chromium centers demonstrated competence in hydrogen atom abstraction chemistry with enhanced stability and reactivity compared to dissolved ions.

Conclusions:

• A straightforward salt metathesis route enables the preparation of reactive porous solids.
• Site-isolated chromium(II) centers within the porous solid are accessible and catalytically active.
• This approach offers a promising strategy for developing stable and reactive heterogeneous catalysts based on coordination cages.