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

The stepwise addition of increasing amounts of Au(PPh 3 )Cl to [HRu 4 (CO) 12 ] 3- (1) results in the sequential formation of [HRu 4 (CO) 12 (AuPPh 3 )] 2- (2), [HRu 4 (CO) 12 (AuPPh 3 ) 2 ] - (3), and HRu 4 (CO) 12 (AuPPh 3 ) 3 (4). Alternatively, 4 can be obtained upon addition of HBF 4 ·Et 2 O (two mole equivalents) to 3. Further addition of acid to 3 (three mole equivalents) results in the formation of the tetra-aurated cluster Ru 4 (CO) 12 (AuPPh 3 ) 4 (5). Compounds 2-5 have been characterized by IR, 1 H and 31 P{ 1 H} NMR spectroscopies. Moreover, the molecular structures of 3-5 have been determined by single crystal X-ray diffraction as [NEt 4 ][3]·2CH 2 Cl 2 , 4-b·2CH 2 Cl 2 , 4-a, 5·0.5CH 2 Cl 2 ·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 1 H and 31 P{ 1 H} 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.