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 center dot 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]center dot 2CH2Cl2, 4-b center dot 2CH2Cl2, 4-a, 5 center dot 0.5CH2Cl2 center dot solv, and 5 center dot 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 AuMIDLINE HORIZONTAL ELLIPSISAu 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.Carbonyl clusters containing HRu4Au, HRu4Au2, HRu4Au3, and Ru4Au4 cores have been obtained and characterized by spectroscopic, structural and computational methods, revealing their aurophilicity, structural isomerism and fluxionality.