Assembly of tetranuclear ruthenium complexes with planar metal core by condensation of two diruthenium units using bridging ligands: Synthesis and molecular structure of [Ru4(CO)8{μ2-P(Cy)2}4] and [Ru4(CO)8{μ4-P(Cy)}2{μ2-P(Cy)2}2] (Cy = cyclohexyl)

Article abstract of DOI:10.1002/hlca.19940770213

The dinuclear complexes [Ru₂(CO)₆{μ-P(Cy)₂}₂] (1) or [Ru₂(CO)₄{μ-(HCO₂)}₂{P(Cy)₂H}₂] (2) react in THF solution at 160° to give the tetranuclear complexes [Ru₄(CO)₈{μ₂-P(Cy)₂}₄] (3) and [Ru₄(CO)₈{μ₄-P(Cy)}₂{μ₂-P(Cy)₂}₂] (4), as well as the trinuclear complex [Ru₃(CO)₇(μ₃-H){μ₂-P(Cy)₂}₃] (5). If the reaction is performed at 200°, the bicapped tetranuclear species 4 is obtained in a higher yield, whereas 3 and 5 are formed in trace amounts only. The phenylderivatives [Ru₂(CO)₆{μ-P(Ph)₂}₂] (6) or [Ru₂(CO)₄{μ-(EtCO₂)}₂{P(Ph)₂H}₂] (7) react in a similar manner to give only the complex [Ru₄(CO)₈{μ₄-P(Ph)}₂{μ₂-P(Ph)₂}₂] (8), analogous to 4. The molecular structure of 3 consists of a planar framework of four Ru-atoms, each Ru-Ru bond being bridged by a μ₂-dicyclohexylphosphino ligand. The complex 4 represents a planar rectangular Ru core, both faces being capped by μ₄-cyclohexylphosphinidene ligands and two opposite edges being bridged by μ₂-dicyclohexylphosphino ligands.