Abstract
n solution, [(PMe2Ph)(2)PtB10H12] (1) and PMe2Ph exist in dynamic equilibrium with [(PMe2Ph)(3)PtB10H12] (2). The activation energy for the dynamic process, Delta G(double dagger), is ca. 63 kJ mol(-1) at +17 degrees C, with Delta S being ca. 335 J mol(-1) deg(-1) and Delta H ca. 105 kJ mol(-1) for the equilibrium.
At low temperatures a rocking fluxionality of the {Pt(PMe2Ph)(3)} unit versus the {eta(4)-B10H12} unit in 2 becomes apparent, with an activation energy Delta G(double dagger) of ca. 28 kJ mol(-1) at ca. -105 degrees C. Compound 2 is characterized by NMR spectroscopy and by a single-crystal X-ray diffraction analysis, for which the results suggest that, in contrast to the common view, the extra electron pair gained by the metal-atom center in going from 1 to 2 does not disrupt the cluster electron count proper nor the observed nido electronic structure and geometry.