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-µ10,11-H-7,8,9-C2PtB8H10] and [9-H-9,10-(Et3P)2-7,8,9-C2PtB8H9]

Abstract

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-C₂PtB₈H₁₀](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-C₂PtB₈H₉](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.