Ruthenium Trichloride Catalyst in Water: Ru Colloids versus Ru Dimer Characterization Investigations

Area of Science:

• Catalysis
• Inorganic Chemistry
• Materials Science

Background:

• Ruthenium catalysts are effective for C-H bond functionalization.
• The precise nature of ruthenium(III) trichloride in aqueous solutions and its active catalytic species remain poorly understood.
• Understanding the active species is crucial for optimizing catalytic performance and reaction selectivity.

Purpose of the Study:

• To elucidate the true nature of ruthenium(III) trichloride in water.
• To identify the active ruthenium species responsible for efficient cycloalkane oxidation.
• To provide insights into the Csp3-H bond functionalization mechanism.

Main Methods:

• Physicochemical characterization including transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS).
• X-ray scattering and absorption analyses to probe the electronic and structural properties of ruthenium species.
• Extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the local coordination environment and oxidation state.

Main Results:

• Spherical nanoobjects (1.75 nm) were observed via TEM and SAXS, initially suggesting reduced species.
• X-ray analyses ruled out metallic nanoparticles, indicating the formation of a water-soluble complex with Ru-O and Ru-Cl bonds.
• EXAFS confirmed an oxygen-bridged diruthenium complex, [Ru(OH)xCl3-x]2(μ-O), in a high oxidation state.

Conclusions:

• The active catalytic species is an oxygen-bridged diruthenium complex, not metallic nanoparticles.
• This study clarifies the speciation of ruthenium(III) trichloride in water, crucial for its catalytic applications.
• The findings highlight the importance of advanced spectroscopic techniques in accurately characterizing nanomaterials and catalytic intermediates.