Nucleophilic addition reactions on the electron-deficient cluster dication[H4Ru4(C6H6)(4)](2+): synthesis and structural characterisation of the water-soluble cluster cations [H3Ru4(C6H6)(4)(CO)](+)and [H3Ru4(C6H6)(4)(OH)](2+)

The electron-deficient (58e) cluster cation [H4Ru4(C6H6)(4)](2+) 1 was foun d to react in aqueous solution with simple nucleophiles to give electron-pr ecise (60e) clusters. With carbon monoxide, the cluster cation [H3Ru4(C6H6) (4)(CO)](+) 3 is formed. The reaction with water needs NaN3 as catalyst and yields the cluster dication [H3Ru4(C6H6)(4)(OH)](2+) 4a; the reaction with alcohols leads to the analogous clusters [H3Ru4(C6H6)(4)(OR)](2+) (R=Me: 4 b, R=Et: 4c, R=PhCH2: 4d, R=Ph: 4e, R=4-EtC6H4: 4f). The single-crystal X-r ay structure analyses of the chloride salts of 3 and 4a reveal a tetrahedra l Ru-4 metal core. Each ruthenium atom is coordinated by a eta (6)-benzene ligand, while the carbonyl or hydroxo ligands are found as mu (3) capping l igands over a triangular face of the Ru-4 tetrahedron.