Two types of tetrasubstitution in [H4Ru4(CO)12]: spectroscopic characterization and crystal structure determination of [H4Ru4(CO)8(PMe2Ph)4] and [H2Ru4(CO)9(PMe2Ph)4]

Two tetrasubstituted tetranuclear ruthenium clusters containing dimethylphenylphosphine [H4Ru4(CO)8(PMe2Ph)4] and [H2Ru4(CO)9(PMe2Ph)4] were prepared and characterized spectroscopically as well as by X-ray crystallography. Both compounds show a structure based on the usual 60-electron tetrahedral framework with each ruthenium atom being bonded to one phosphine ligand. In the case of the nonacarbonyl derivative, one of the ruthenium atoms has one terminal carbonyl group and is also bonded to two semibridging carbonyl groups; two other metal–metal bonds are bridged by the hydride groups. In the case of the octacarbonyl compound all the ruthenium atoms are bonded to two terminal carbonyls and to two bridging hydrides. NMR spectroscopical information of [H4Ru4(CO)8(PMe2Ph)4] suggests the presence of two isomers in solution which we propose to have D2d and Cs symmetries. The observation of the NMR properties gives some observations about conditions that favour coupling between substituents in different ruthenium atoms.