ASSEMBLY OF TETRANUCLEAR RUTHENIUM COMPLEXES WITH PLANAR METAL CORE BY CONDENSATION OF 2 DIRUTHENIUM UNITS USING BRIDGING LIGANDS - SYNTHESIS AND MOLECULAR-STRUCTURE OF [RU4(CO)8(MU(2)-P(CY)2)4] AND [RU4(CO)8(MU(4)-P(CY))2(MU(2)-P(CY)2)2] (CY=CYCLOHEXYL)

The dinuclear complexes [Ru2(CO)6{mu-P(Cy)2}2] (1) or [RU2(CO)4{mu-(HCO2-)}2{P(Cy)2H}2](2) react in THF solution at 160-degrees to give the tetranuclear complexes [Ru4(CO)8{mu2-P(Cy)2}4] (3) and [Ru4(CO)8{mu4-P(Cy)}2{mu2-P(Cy)2}2] (4), as well as the trinuclear complex [Ru3(CO)7(mu2-H){mu2-P(Cy)2}3] (5). If the reaction is performed at 200-degrees, the bicapped tetranuclear species 4 is obtained in a higher yield, whereas 3 and 5 are formed in trace amounts only. The phenyl derivatives [RU2(CO)6{mu-P(Ph)2}2] (6) or [RU2(CO)4{mu-(EtCO2)}2{P(Ph)2H}2] (7) react in a similar manner to give only the complex [RU4(CO)8{mu4-P(Ph)}2{mu2-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 mu2-dicyclohexylphosphino ligand. The complex 4 represents a planar rectangular Ru core, both faces being capped by mu4-cyclohexylphosphinidene ligands and two opposite edges being bridged by mu2-dicyclohexylphosphino ligands.