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 . Carbonyl clusters containing HRu 4 Au, HRu 4 Au 2 , HRu 4 Au 3 , and Ru 4 Au 4 cores have been obtained and characterized by spectroscopic, structural and computational methods, revealing their aurophilicity, structural isomerism and fluxionality.