Synthesis, characterisation and molecular structures of the closo and pseudocloso heptamethylindenyl carbarhodaboranes 1-Ph-3-(η-C₉Me₇)-3,1,2-closo-RhC₂B ₉H₁₀ and 1,2-Ph₂-3-(η-C₉Me ₇)-3,1,2-pseudocloso-RhC₂B₉H₉. Experimental assignment of the ¹¹B NMR ...

Title full: Synthesis, characterisation and molecular structures of the closo and pseudocloso heptamethylindenyl carbarhodaboranes 1-Ph-3-(?-C₉Me₇)-3,1,2-closo-RhC₂B ₉H₁₀ and 1,2-Ph₂-3-(?-C₉Me ₇)-3,1,2-pseudocloso-RhC₂B₉H₉. Experimental assignment of the ¹¹B NMR spectrum of a pseudocloso carbametallaborane. The reaction between [{RhCl₂(?-C₉Me₇)}₂] and Tl₂[7-Ph-8-R-7,8-nido-C₂B₉H₉] (R = H or Ph) in CH₂Cl₂ afforded the heptamethylindenyl carbarhodaboranes 1-Ph-3-(?-C₉Me₇)-3,1,2-RhC₂B ₉H₁₀ 1 and 1,2-Ph₂-3-(?;-C₉Me₇)-3,1,2-RhC ₂B₉H₉ 2, respectively, in good yields. The ¹¹B NMR chemical shifts of 1 and 2 showed that they possess closo and pseudocloso structures, respectively. Compound 1 was found to be fluctional in solution at room temperature via rotation of the Ph substituent, but cooling below ca. 230 K arrested this process, presumably by locking the indenyl ligand into its preferred cisoid conformation and preventing phenyl rotation. An X-ray diffraction study of a single crystal of 1 confirmed both the closo nature of the cage and the cisoid conformation, but additionally showed that, of two possible cisoid conformations, the one adopted places the cage phenyl substituent underneath the six-membered ring of the indenyl group. Compound 2 was also subjected to crystallographic analysis, which confirmed the pseudocloso nature of the cage. Again, the relative conformation of the two ?-bonded ligands is cisoid. An ¹¹B-¹¹B COSY spectrum of compound 2, the first to be recorded from a pseudocloso species, allowed experimental assignment of the ¹¹B chemical shifts which were in excellent agreement with those previously obtained theoretically.