Phosphorus monoxide coordination chemistry: Synthesis and structural characterization of tetranuclear clusters containing a PO ligand

The clusters Ru-4(CO)(13)PNPr2i(1) and Os-4(CO)(13)(PNPr2i) (4) have been prepared via the reactions of Cl2PNPr2i with respectively [Ru-4(CO)(13)](2-) and the reaction product of Na-2[Os(CO)(4)] and Os-3(CO)(12). The successful synthesis of 4 suggests that the reaction of Na-2[Os(CO)(4)] with OS3(CO)(12) generates [Os-4(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 M(4)(CO)(12)(PNPr2i) (M = -Ru, 2, and Os, 5), which upon chromatography and subsequent metathesis with Et(4)N[CI] afford the [H2NPr2i](+) and [Et(4)N](+) salts of [M(4)(CO)(12)(PO)](-) (M = Ru, 3, and Os, 6), respectively. The structures of 1, 2, 3[H2NPr2i], 4, and 6[Et(4)N] were determined by X-ray crystallography. The M(4)P 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 PNPr2i ligand capping one face of a Ru-4 tetrahedron. The arrangement of metal and-phosphorus atoms in 3[H2NPr2i] and 6[Et(4)N] remains similar to that in 2. The phosphorus monoxide ligand, in each case, triply bridges a M(3) face of the tetrahedral M(4) skeleton with the P-O vector essentially perpendicular to this face. The interatomic P-O distances in 3[H2NPr2i] and 6[Et(4)N] 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 fur the preparation of metal clusters containing a PO ligand.