Highly Reduced Ruthenium Carbide Carbonyl Clusters: Synthesis, Molecular Structure, Reactivity, Electrochemistry, and Computational Investigation of [Ru6C(CO)15]4–

The reaction of [Ru6C(CO)16]2– (1) with NaOH in DMSO resulted in the formation of a highly reduced [Ru6C(CO)15]4– (2), which was readily protonated by acids, such as HBF4·Et2O, to [HRu6C(CO)15]3– (3). Oxidation of 2 with [Cp2Fe][PF6] or [C7H7][BF4] in CH3CN resulted in [Ru6C(CO)15(CH3CN)]2– (5), which was quantitatively converted into 1 after exposure to CO atmosphere. The reaction of 2 with a mild methylating agent such as CH3,I afforded the purported [Ru6C(CO)14(COCH3)]3– (6). By employing a stronger reagent, that is, CF3SO3CH3, a mixture of [HRu6C(CO)16]− (4), [H3Ru6C(CO)15]− (7), and [Ru6C(CO)15(CH3CNCH3)]− (8) was obtained. The molecular structures of 2–5, 7, and 8 were determined by single-crystal X-ray diffraction as their [NEt4]4[2]·CH3CN, [NEt4]3[3], [NEt4][4], [NEt4]2[5], [NEt4][7], and [NEt4][8]·solv salts. The carbyne–carbide cluster 6 was partially characterized by IR spectroscopy and ESI-MS, and its structure was computationally predicted using DFT methods. The redox behavior of 2 and 3 was investigated by electrochemical and IR spectroelectrochemical methods. Computational studies were performed in order to unravel structural and thermodynamic aspects of these octahedral Ru–carbide carbonyl clusters displaying miscellaneous ligands and charges in comparison with related iron derivatives.