Fe₂(μ-E₂)(CO)₆ (E = S, Se, and Te) as Reagents for the Preparation of Mixed-Metal Chalcogenide Clusters

The compounds Fe₂(μ-E₂)(CO)₆, where E = S, Se, and Te, react efficiently with Pt(PPh₃)₂C₂H₄ to afford the new heterometallic clusters, (CO)₆Fe₂(μ₃-E)₂Pt(PPh ₃)₂. This reaction formally involves the homolytic cleavage of the E-E bond in the μ-E₂ precursor complexes and represents a novel route to mixed-metal clusters. ³¹P NMR of (PPh₃)(CO)₅Fe₂(μ₃-S) ₂Pt(PPh₃)₂ (prepared from Fe₂(μ-S₂)(CO)₅(PPh₃)) indicates that the plane of the Pt coordination sphere is perpendicular to the iron-iron vector. The structure of (CO)₆Fe₂(μ₃-Se)₂Pt(PPh ₃)₂ was determined by conventional X-ray crystallographic techniques. The crystals were monoclinic with a = 10.944 (2) Å, b = 16.321 (3) Å, c = 23.135 (4) Å, β = 94.68 (1)°, Z = 4; the space group is P2₁/n. Conventional full-matrix least-squares refinement with nonhydrogen atoms anisotropic and fixed hydrogen atoms isotropic gave R₁ = 0.037 and R₂ = 0.040 for 7119 reflections having 2θ Mo Kᾱ < 58.7° and I > 3σ(I). The structure consists of an isosceles triangle of metal atoms tethered by two capping μ₃-Se moieties. The two Fe(CO)₃ units are mutually bonded, and this fragment closely resembles Fe₂(μ-Se₂)(CO)₆ with an expanded Se-Se vector. We reconcile the reactivity of these μ-E₂ compounds and the chemical dormancy of species such as Ph₂Te₂ and monometallic S₂ complexes as being both electronic and steric (ring strain) in origin.