Polyhedral metallaheteroborane chemistry. Synthesis, spectroscopy, structure and dynamics of eleven-vertex {RhNB9} and {PtCB9} metallaheteroboranes.

Abstract

Reaction between [RhCl(PPh₃)₃] and the [nido-6-NB₉H₁₁]⁻ anion in CH₂Cl₂ yields orange eleven-vertex [8,8-(PPh₃)₂-nido-8,7-RhNB₉H₁₁] (1). Reaction of the [nido-6-CB₉H₁₂]⁻ anion with [cis-PtCl₂(PMe₂Ph)₂] in methanol affords yellow eleven-vertex [9-(OMe)-8,8-(PMe₂Ph)₂-nido-8,7-PtCB₉H₁₀] (2), which is also formed from the reaction of MeOH with [8,8-(PPh₃)₂-nido-8,7-PtCB₉H₁₀] (3). Both compounds have been characterised by single-crystal X-ray diffraction analysis and examined by NMR spectroscopy and have structures based on eleven-vertex nido-type geometries, with the metal centre and the heteroatoms in the adjacent (8)- and (7)-positions on the pentagonal open face. The metal-to-heteroborane bonding sphere of 1 is fluxional, with a ΔG^‡ value of 48.4 kJ mol⁻¹. DFT calculations on the model compounds [8,8-(PH₃)₂-nido-8,7-RhNB₉H₁₁] (1a) and [8,8-(PH₃)₂-nido-8,7-RhSB₉H₁₀] (4a) have been carried out to define the fluxional process and the intermediates involved.