Journal of the Chemical Society, Dalton Transactions p. 335 - 342 (1996)
Update date:2022-07-30
Topics:
Graedler, Ulrich
Weller, Andrew S.
Welch, Alan J.
Reed, David
Title full: 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 spectrum of a pseudocloso carbametallaborane. The reaction between [{RhCl2(η-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-(η-C9Me7)-3,1,2-RhC2B 9H10 1 and 1,2-Ph2-3-(η;-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 η-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.
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(1996)
