Eleven-vertex polyhedral monocarbaplatinaborane chemistry. Structure and fluxionality of [8,8-(PMe<sub>2</sub>Ph)<sub>2</sub>-nido-8,7-PtCB<sub>9</sub>H<sub>11</sub>]
作者:Bohumil Štíbr、Tomáš Jelínek、John D. Kennedy、Xavier L. R. Fontaine、Mark Thornton-Pett
DOI:10.1039/dt9930001261
日期:——
Reaction between [PtCl2(PMe2Ph)2] and [arachno-6-CB9H14]- in CH2Cl2 solution at room temperature yields yellow air-stable eleven-vertex [8,8-(PMe2Ph)2-nido-8,7-PtCB9H11] 1 (46-64%) together with small quantities of ten-vertex [9,9-(PMe2Ph)2-arachno-9,6-PtCB8H12] 2 (0-3%). Crystals of compound 1 are monoclinic, space group P2(1)/n, with a = 1186.8(1), b = 1554.1 (2), c = 1344.1(2) pm, beta = 95.02(1)-degrees and Z = 4. The structure refined to R, R' = 0.0297, 0.031 0 using 3938 data with I > 3sigma(I). The cluster structure is of the nido eleven-vertex type, with the platinum and carbon atoms occupying adjacent positions on the open face. There is some geometrical closure from pure nido, so that the gross cluster structure tends towards intermediacy between those of [7,7-(PMe2Ph)2-nido-7-PtB10H12] 4 and of the closo-structured species [1,1-(PMe2Ph)2-1,2,3-PtC2B8H10] 3. The NMR properties of 1 are reported and assessed for intermediacy between those of 3 and 4, and the analytical utility of NMR spectroscopy in assessing the metal-to-cluster bonding is developed by comparison with non-metallated species. The metal-to-carborane bonding sphere of compound 1 is fluxional, with DELTAG(double-dagger) ca. 62 kJ mol-1. The fluxional process involves an interconversion of enantiomers with the platinum centre and the bridging hydrogen atom migrating around the open face of the CB9H10} cage while the (PMe2Ph)2} exo polyhedral ligand sphere undergoes a half-twist.