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 H2 atmosphere afforded the 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 reaction of 1 with [Ir(CO)4]– in refluxing THF. The hydride carbonyl clusters 2-4 were fully characterized by IR and 1H NMR spectroscopy, and the molecular structures of 2 and 3 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 solvent and hydrogen source. The results obtained with these heterometallic Ru-Ir clusters were compared to 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 atmosphere, as well as H2 pressure.