Reactions of heteroboranes. Synthesis of [2,2-(PPh3)2-1,2-SePtB10H10]·CH2CL2, its crystal and molecular structure and that of SeB11H11

Abstract

The reaction (refluxing ethanol) of [Pt(PPh₃)₄] with closo-SeB₁₁H₁₁ affords two products. One, characterised spectroscopically, is [PtH(PPh₃)₃][SeB₁₀H₁₁]. The second product, isolated after recrystallisation from dichloromethane–ethanol solution is [2,2-(PPh₃)₂-1,2-SePtB₁₀H₁₀]·CH₂Cl₂(1). An X-ray diffraction study shows crystals of (1) to be triclinic, space group P, with two formula units in a cell of dimensions a= 12.837(3), b= 14.534(2), c= 11.898(3)Å, α= 96.59(2), β= 107.31(2), γ= 81.89(l)°. Using 5 046 reflections, the structure was refined to R= 0.028. The dodecahedral SePtB₁₀ cage has Se and Pt atoms occupying adjacent sites. The principal dimensions include the bond lengths Pt–Se 2.676(l), Se–B 2.098(9)–2.210(6), Pt–P 2.326(l) and 2.350(2), and Pt–B 2.231(8)–2.31 l(6)Å and an interplanar angle of 80.0° between the plane containing the PtP₂ unit and that containing the Se and Pt atoms and passing through the mid-point of the B(2)–B(3) bond opposite the Se atom. The crystal and molecular structure of SeB₁₁H₁₁ was studied by X-ray diffraction methods in an attempt to provide more information on Se–B bonding. Crystals of SeB₁₁H₁₁ are cubic, space group Pa3, with four molecules in a cell, a= 9.847(3)Å. The structure was refined to R= 0.075 for 164 reflections. The molecule lies on a site with crystallographic symmetry; the electron density and refinement are consistent with scrambling of the Se atom and eleven B–H groups over the twelve dodecahedral positions. This precluded any precise determination of Se–B bond distances.