Heterometallic Ru–Ir carbonyl clusters as catalyst precursors for hydrogenation and hydrogen transfer reactions

Abstract

Reaction of [HRu₃(CO)₁₁]⁻ (1) with [Ir(COD)Cl]₂ in CH₂Cl₂ under a H₂ atmosphere afforded dihydride [H₂Ru₃Ir(CO)₁₂]⁻ (2), which was quantitatively protonated to H₃Ru₃Ir(CO)₁₂ (3) by strong acids such as HBF₄·Et₂O. The related mono-hydride [HRu₃Ir(CO)₁₂]²⁻ (4) was obtained by deprotonation of 2 with a strong base such as KO^tBu, or by the reaction of 1 with [Ir(CO)₄]⁻ in refluxing THF. Hydride carbonyl clusters 2–4 were fully characterized by IR and ¹H NMR spectroscopies, and the molecular structures of 2 and 3 were determined by single-crystal X-ray diffraction (SC-XRD). The location of the hydride ligands within the tetrahedral cages of these clusters was further corroborated by computational studies employing DFT methods. Clusters 2–4 were tested as catalyst precursors for transfer hydrogenation on the model substrate 4-fluoroacetophenone, using ⁱPrOH as a solvent and a hydrogen source. The results obtained using these heterometallic Ru–Ir clusters were compared to those using homometallic 1, evidencing a significant difference, particularly regarding the effect of the base on catalysis. Heterometallic cluster 2 was also tested in the hydrogenation of trans-cinnamaldehyde in ⁱPrOH at refluxing temperature both under N₂ and H₂ atmospheres, and H₂ pressure.