Phosphorus Monoxide Coordination Chemistry: Synthesis and Structural Characterization of Tetranuclear Clusters Containing a PO Ligand

Abstract

The clusters Ru4(CO)13(PNPri2) (1) and Os4(CO)13(PNPri2) (4) have been prepared via the reactions of Cl2PNPri2 with respectively [Ru4(CO)13]2- and the reaction product of Na2[Os(CO)4] and Os3(CO)12. The successful synthesis of 4 suggests that the reaction of Na2[Os(CO)4] with Os3(CO)12 generates [Os4(CO)13]2-, thus providing a relatively easy route for the preparation of this dianion. Thermal decarbonylation of 1 and 4 affords the tetranuclear clusters M4(CO)12(PNPri2) (M = Ru, 2, and Os, 5), which upon chromatography and subsequent metathesis with Et4N[Cl] afford the [H2NPri2]+ and [Et4N]+ salts of [M4(CO)12(PO)]- (M = Ru, 3, and Os, 6), respectively. The structures of 1, 2, 3[H2NPri2], 4, and 6[Et4N] were determined by X-ray crystallography. The M4P frameworks in 1 and 4 form a square pyramidal arrangement with the P atom occupying a basal position. The molecular structure of 2 reveals a five-vertex polyhedron with the PNPri2 ligand capping one face of a Ru4 tetrahedron. The arrangement of metal and phosphorus atoms in 3[H2NPri2] and 6[Et4N] remains similar to that in 2. The phosphorus monoxide ligand, in each case, triply bridges a M3 face of the tetrahedral M4 skeleton with the P−O vector essentially perpendicular to this face. The interatomic P−O distances in 3[H2NPri2] and 6[Et4N] suggest double-bond character for the P−O moiety. Cleavage of the PN bond of an aminophosphinidene ligand followed by P−O bond formation may have general applicability for the preparation of metal clusters containing a PO ligand.