Eleven-vertex Polyhedral Monocarbaplatinaborane Chemistry. Structure and Fluxionality of

Article abstract of DOI:10.1039/DT9930001261

Reaction between and arachno-6-CB9H14>(1-) in CH2Cl solution at room temperature yields yellow air-stable eleven-vetex <8,8-(PMe2Ph)2-nido-8,7-PtCB9H11> 1 (46-64percent) together with small quantities of ten-vertex <9,9-(PMe2Ph)2-arachno-9,6-PtCB8H12> 2 (0-3percent).Crystals of compound 1 are monoclinic, space group P2₁/n, with a = 1186.8(1), b = 1554.1(2), c = 1344.1(2) pm, β = 95.02(1) deg and Z = 4.The structure refined to R,R'= 0.0297, 0.0310 using 3938 data with I > 3?(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 ΔG(excit.)₃₁₃ ca. 62 kJ mol¹.The fluxional process involves and interconversion of enantiomers with the platinum centre and the bridging hydrogen atom migrating around the open face of the cage while the <(PMe2Ph)2> exo polyhedral ligand sphere undergoes a half-twist.

Full text of DOI:10.1039/DT9930001261

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