11-VERTEX POLYHEDRAL MONOCARBAPLATINABORANE CHEMISTRY - STRUCTURE ANDFLUXIONALITY OF [8,8-(PME2PH)2-NIDO-8,7-PTCB9H11]

Reaction between [PtCl2(PMe2Ph)2] and [arachno-6-CB9H14]- in CH2Cl2 so lution at room temperature yields yellow air-stable eleven-vertex [8,8 -(PMe2Ph)2-nido-8,7-PtCB9H11] 1 (46-64%) together with small quantitie s of ten-vertex [9,9-(PMe2Ph)2-arachno-9,6-PtCB8H12] 2 (0-3%). Crystal s 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 wit h I > 3sigma(I). The cluster structure is of the nido eleven-vertex ty pe, with the platinum and carbon atoms occupying adjacent positions on the open face. There is some geometrical closure from pure nido, so t hat the gross cluster structure tends towards intermediacy between tho se of [7,7-(PMe2Ph)2-nido-7-PtB10H12] 4 and of the closo-structured sp ecies [1,1-(PMe2Ph)2-1,2,3-PtC2B8H10] 3. The NMR properties of 1 are r eported and assessed for intermediacy between those of 3 and 4, and th e analytical utility of NMR spectroscopy in assessing the metal-to-clu ster bonding is developed by comparison with non-metallated species. T he 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 bri dging hydrogen atom migrating around the open face of the {CB9H10} cag e while the {(PMe2Ph)2} exo polyhedral ligand sphere undergoes a half- twist.