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⁺<b>1</b> was found to react in aqueous solution with simple nucleophiles to give electron-precise (60e) clusters. With carbon monoxide, the cluster cation [H₃Ru₄(C₆H₆)₄(CO)]⁺<b>3</b> is formed. The reaction with water needs NaN₃ as catalyst and yields the cluster dication [H₃Ru₄(C₆H₆)₄ (OH)]²⁺<b>4a</b>; the reaction with alcohols leads to the analogous clusters [H₃Ru₄(C₆H₆)₄ (OR)]²⁺ (R = Me: <b>4b</b>, R = Et: <b>4c</b>, R = PhCH₂: <b>4d</b>, R = Ph: <b>4e</b>, R = 4-EtC₆H₄: <b>4f</b>). The single-crystal X-ray structure analyses of the chloride salts of <b>3</b> and <b>4a</b> reveal a tetrahedral Ru₄ metal core. Each ruthenium atom is coordinated by a η⁶-benzene ligand, while the carbonyl or hydroxo ligands are found as µ₃ capping ligands over a triangular face of the Ru₄ tetrahedron.