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

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.