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

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 KOtBu, 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.