Synthesis and characterization of high-nuclearity osmium–platinum cluster compounds. The molecular structures of [Os6Pt2(CO)16(C8H12)2] and [Os6Pt2(CO)16(C8H12){P(OMe)3}2](C8H12= cyclo-octa-1,5-diene)

Abstract

The reaction of [Os₆(CO)_{18 –n}(NCMe)_n](n= 1 or 2) with [Pt(C₈H₁₂)₂](C₈H₁₂= cyclo-octa-1,5-diene) results in the formation of [Os₆Pt₂(CO)₁₇(C₈H₁₂)₂](1) and [Os₆Pt₂(CO)₁₆(C₈H₁₂)₂](2) respectively. Complex (1) is known to have a Pt-bicapped octahedral geometry. Complex (2) crystallizes in the monoclinic space group C2/c with a= 21.178(3), b= 11.683(2), c= 17.383(2)Å, β= 113.83(1)°, Z= 4. The structure has been refined to R′= 0.034 (R= 0.044) for 2 675 unique diffractometer data. The complex possesses the unusual metal-core geometry of two edgefused Os tetrahedra, one of which is Pt-bicapped. This cluster is a 108-electron system and its metallic framework cannot be explained by any of the conventional electron-counting schemes. The cluster is formally electronically unsaturated and this is reflected in its apparent reactivity. Complex (2) reacts immediately with CO or P(OMe)₃ to yield cluster (1) or complex [Os₆Pt₂(CO)₁₆(C₈H₁₂){P(OMe)₃}₂](3), respectively. Complex (3) crystallizes in the monoclinic space group P2₁/c with a= 19.160(4), b= 10.963(2), c= 21.277(6)Å, β= 99.40(2)°, Z= 4, and the molecular structure has been refined to R′= 0.073 (R= 0.086) for 2 818 unique data. The molecular geometry of (3) can be described as a bicapped tetrahedron of Os atoms having two Ptcapped faces. Complex (3) is also a 108-electron system but its geometry can be rationalized by using any of the electron-counting schemes. Cluster (3) reacts immediately with CO to give a compound which has the same metal-core geometry as (1). The relationship between the structures of (1), (2), and (3) is discussed briefly in terms of transformations of the mixed-metal cluster skeleton.