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

Abstract

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.