Synthesis of [Ru4(μ3-η2-CO)(CO)9{μ-(RO)2PN(Et)P(OR)2}2] (R = Me or Pri): Butterfly clusters of ruthenium containing a triply bridging carbonyl ligand with an unusual mode of coordination. Crystal structure of [Ru4(μ3-η2-CO)(CO)9{μ-(MeO)2PN(Et)P(OMe)2}2]

Reaction of [Ru 3 (CO) 12 ] with a two molar proportion of (RO) 2 PN(Et)P(OR) 2 (R = Me or Pr i ) in benzene under reflux affords a number of products including [Ru 3 (CO) 10 {μ-(RO) 2 PN(Et)P(OR) 2 }], [Ru 3 (CO) 9 {μ-(RO) 2 PN(Et)P(OR) 2 }{η 1 -(RO) 2 PN(Et)P(OR) 2 }] and, as the major species, the tetranuclear derivative [Ru 4 (μ 3 -η 2 -CO)(CO) 9 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ]. An X-ray diffraction study of [Ru 4 (μ 3 -η 2 -CO)(CO) 9 {μ-(MeO) 2 PN(Et)P(OMe) 2 } 2 ] has revealed that the skeletal framework adopts a butterfly structure and that one of the carbonyl groups functions as a triply bridging four-electron donor ligand capping the two wing-tip and one of the hinge ruthenium atoms.