Metallaborane Chemistry.  Part 13.  Direct Insertion of a Platinum Nucleophile into nido-5,6-C₂B₈H₁₂:  Synthesis and Structural Elucidation of [9-H-9,9-(Et₃P)₂-m_10,11-H-7,8,9-C₂PtB₈H₁₀] and [9-H-9,10-(Et₃P)₂-7,8,9-C₂PtB₈H₉]

The reaction (room temperature, diethyl ether) of [Pt₂(μ-cod)(PEt₃)₄] (cod = cyclo-octa-1,5-diene) with nido-5,6-C₂B₈H₁₂ affords [9-H-9,9(Et₃P)₂-μ_10,11-H-7,8,9-C ₂PtB₈H₁₀] (1), structurally characterised by X-ray diffraction. Crystals are orthorhombic, space group P2₁2₁2₁, with four molecules in a unit cell of dimensions a = 14.825(4), b = 10.1367(13), and c = 16.1193(15) Å. Using 3 303 amplitudes recorded at 293 K the structure has been refined to R = 0.0575 (R′ = 0.0611). The cage of (1) approximates to a nido-icosahedron with a [graphic omitted] open face. Presumably the B-B connectivity in this face is hydrogen-bridged, but the bridge atom was not located in the crystallographic study. Thermolysis of (1) (100 °C toluene) releases one mol equiv. of H₂ affording [9-H-9,10-(Et₃P)₂-7,8,9-C₂PtB₈H ₉] (2), in which μ-H is lost and phosphine transfer from Pt to an adjacent facial B has occurred. Crystals are monoclinic, space group P2₁/c with a = 9.7813(16), b = 12.312(3) c = 20.519(3) Å, β = 99.053(16)°, and Z = 4. The structure was refined to R′ = 0.0578 (R′ = 0.0552) for 3 194 data measured at 293 K. The polyhedron of (2), formally a Pt^II species, shows distortion towards a closed octadecahedral architecture. The mechanism of the transformation of (1) into (2) is discussed in relation to the influence of the stereochemical changes involved.