9-VERTEX POLYHEDRAL MONOCARBAPLATINABORANE CHEMISTRY - ISOLATION, MOLECULAR-STRUCTURE AND NUCLEAR-MAGNETIC-RESONANCE PROPERTIES OF [6,6-(PPH3)2-ARACHNO-6,4-PTCB7H11]

Reaction between [Pt(PPh3)4] and nido-1-CB8H12 1 results in the format ion of [6,6-(PPh3)2-arachno-6,4-PtCB7H11] 2 as a yellow crystalline so lid in 26% yield. The product 2 is characterised by NMR spectroscopy a nd single-crystal X-ray diffraction analysis. Crystals (from CH2Cl2-he xane) are triclinic, space group P1BAR, with a = 974.3(2), b = 1237.5( 2), c = 1771.3(3) pm, alpha = 95.26(1), beta = 95.43(1), gamma = 110.1 0(1)-degrees and Z = 2. The structure has been refined to R(R') = 0.02 56 (0.0394) for 6324 reflections [F(o) > 2.0sigma(F(o))]. The molecula r structure is based on a nine-vertex arachno cluster with the platinu m and carbon atoms in projecting open face 6- and 4-positions respecti vely. The B-11, H-1 and P-31 NMR parameters have been measured and ass igned to structural positions, and the B-11 and H-1 shielding patterns are compared to those of the related non-platinum species arachno-4,5 -C2B7H13 7 and arachno-4,6-C2B7H13 8. Incidental to this work the prev iously unreported H-1 shielding behaviour of the carbaboranes 1, 7 and 8 have also been measured and assigned.