Spectroscopic Study of Sol-Gel Entrapped Triruthenium Dodecacarbonyl Catalyst Reveals Hydride Formation

Triruthenium dodecacarbonyl exhibits increased catalytic activity toward hydrogenation reactions when encapsulated in alumina sol-gels. In this study, we demonstrate structural and electronic changes induced by the encapsulation process. Fourier transform infrared (FTIR) spectroscopy reveals that the carbonyl vibrational modes dramatically red shift during aging in the sol-gel glass. These shifts are attributed to the formation of the metal hydride: [HRu₃(CO)₁₁]^-. A comparison to the FTIR spectrum of synthesized [NEt₄][HRu₃(CO)₁₁] confirms this assignment. XPS studies show that the Ru 3d_5/2 peak of [HRu₃(CO)₁₁]^- also shifts to lower binding energy, consistent with an increased electron density on the Ru nuclei compared to Ru₃(CO)₁₂ and confirmed by density functional calculations. This study should open the door to further investigations into the hydride's role in the previously observed catalytic activity. To the best of our knowledge, this is the first study to identify the presence of [HRu₃(CO)₁₁]^- in the alumina sol-gel.