Synthesis, molecular structure and fluxional behavior of the elusive [HRu4(CO)12]3- carbonyl anion

Peraurated ruthenium hydride carbonyl clusters: aurophilicity, isolobal analogy, structural isomerism, and fluxionality

The stepwise addition of increasing amounts of Au(PPh3)Cl to [HRu4(CO)12]3- (1) results in the sequential formation of [HRu4(CO)12(AuPPh3)]2- (2), [HRu4(CO)12(AuPPh3)2]- (3), and HRu4(CO)12(AuPPh3)3 (4). Alternatively, 4 can be obtained upon addition of HBF4·Et2O (two mole equivalents) to 3. Further addition of acid to 3 (three mole equivalents) results in the formation of the tetra-aurated cluster Ru4(CO)12(AuPPh3)4 (5). Compounds 2-5 have been characterized by IR, 1H and 31P{1H} NMR spectroscopies. Moreover, the molecular structures of 3-5 have been determined by single crystal X-ray diffraction as [NEt4][3]·2CH2Cl2, 4-b·2CH2Cl2, 4-a, 5·0.5CH2Cl2·solv, and 5·solv crystalline solids. Two different isomers of 4, that is 4-a and 4-b, have been crystallographically characterized and their rapid interconversion in solution was studied by variable temperature 1H and 31P{1H} NMR spectroscopies. Weak aurophilic Au⋯Au contacts have been detected in the solid state structures of 3-5. Computational studies have been performed in order to elucidate bonding and isomerism, as well as to predict the possible structure of the elusive species 2.

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.

2-D Molecular Alloy Ru-M (M = Cu, Ag, and Au) Carbonyl Clusters: Synthesis, Molecular Structure, Catalysis, and Computational Studies

The reactions of [HRu₃(CO)₁₁]⁻ (1) with M(I) (M = Cu, Ag, and Au) compounds such as [Cu(CH₃CN)₄][BF₄], AgNO₃, and Au(Et₂S)Cl afford the 2-D molecular alloy clusters [CuRu₆(CO)₂₂]⁻ (2), [AgRu₆(CO)₂₂]⁻ (3), and [AuRu₅(CO)₁₉]⁻ (4), respectively. The reactions of 2–4 with PPh₃ result in mixtures of products, among which [Cu₂Ru₈(CO)₂₆]^2– (5), Ru₄(CO)₁₂(CuPPh₃)₄ (6), Ru₄(CO)₁₂(AgPPh₃)₄ (7), Ru(CO)₃(PPh₃)₂ (8), and HRu₃(OH)(CO)₇(PPh₃)₃ (9) have been isolated and characterized. The molecular structures of 2–6 and 9 have been determined by single-crystal X-ray diffraction. The metal–metal bonding within 2–5 has been computationally investigated by density functional theory methods. In addition, the [NEt₄]⁺ salts of 2–4 have been tested as catalyst precursors for transfer hydrogenation on the model substrate 4-fluoroacetophenone using ⁱPrOH as a solvent and a hydrogen source.

Heterometallic Ru−M (M = Cu, Ag, and Au) carbonyl clusters possessing a 2-D metal core have been investigated by structural and computational methods and tested as catalyst precursors for transfer hydrogenation.