Enhanced slip distortions in 1-phenyl-2-methyldicarbaplatinaboranes. Conformational destabilisation in the isomerisation of 1-phenyldicarbaplatinaboranes

The compounds TI₂[7-Ph-8-Me-7,8-nido-C₂B₉H₉], [C₅H₁₀NH₂][7-Ph-8-Me-7,8-nido-C ₂B₉H₁₀], 1-Ph-2-Me-3,3-L₂-3,1,2-PtC₂B₉H₉ [L = PMe₂Ph, PEt₃, PPh₃ or P(C₆H₄Me-p)₃] have been prepared and characterised. The platinum complexes were obtained from the reactions between TI₂[7-Ph-8-Me-7,8-nido-C₂B₉H₉] and the appropriate [PtCl₂(PR₃)₂] species. Crystallographic studies upon the compounds where L = PEt₃ and two crystalline modifications of that where L = PPh₃ afforded evidence of a substantial influence of intramolecular crowding upon the observed structures, so that the lateral slippage (?) of the metal fragment is significantly enhanced: ? = 0.74 and 0.94 and 0.91 Å respectively. These compounds do not isomerise under conditions which produce rearrangement in the corresponding (less-congested) derivatives of 1-phenylcarbaborane, consistent with the proposed conformational destabilisation in the latter system.