Synthesis and characterisation of tetranuclear ruthenium polyhydrido clusters with pseudo-tetrahedral geometryElectronic supplementary information (ESI) available: Crystal structures. CCDC 1524828 (5), 1519872 (7), 1519873 (8), and 1519875 (10′). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt04523e

Dicationic tetranuclear ruthenium octahydride [(Cp*Ru) 4 H 8 ] 2+ ( 5 ) with tetrahedral geometry was obtained by reaction of dinuclear ruthenium tetrahydride (Cp*Ru) 2 (μ-H) 4 ( 1 ) with an excess of Brønsted acids, such as HBF 4 ·OEt 2 , in toluene. Monocationic tetraruthenium heptahydride [(Cp*Ru) 4 H 7 ] + ( 7 ) was obtained by dropwise addition of a diluted acid to a rigorously stirred solution of 1 at ambient temperature. Dication 5 was converted into monocationic heptahydrido complex 7 in high yield by treatment with sodium methoxide or sodium hydride. The direct conversion of 5 into neutral hexahydrido complex (Cp*Ru) 4 H 6 ( 8 ) was achieved in a highly efficient manner by treating 5 with LiAlH 4 in tetrahydrofuran (THF). The conversion of 5 into 8 was reversible, and the addition of a Brønsted acid to 8 gave 5 via the formation of 7 as an intermediate. Tetranuclear complex 8 was directly obtained from 1 by heating it in THF at 70 °C. Complex 8′ and tetraruthenium tetrahydride (Cp Et Ru) 4 H 4 ( 10′ ), where 8′ and 10′ possessed η 5 -C 5 EtMe 4 ligands instead of Cp* ligands, were mutually related by the elimination/addition of dihydrogen. The structures of 5 , 7 , 8 , and 10′ were determined by X-ray diffraction, and the Ru 4 core structure and the coordination mode of hydrido ligands were discussed based on density functional theory (DFT) calculations for model compounds where the methyl groups of Cp* ligands were replaced with hydrogen atoms. A series of tetranuclear ruthenium polyhydrido complexes with electric charges from +2 to 0 was synthesized.