SYNTHESIS, CHARACTERIZATION AND MOLECULAR-STRUCTURES OF THE CLOSO ANDPSEUDOCLOSO HEPTAMETHYLINDENYL CARBARHODABORANES 1-PH-3-(ETA-C(9)ME(7))-3,1,2-CLOSO-RHC2B9H10 AND PH(2)-3-(ETA-C(9)ME(7))-3,1,2-PSEUDOCLOSO-RHC2B9H9 - EXPERIMENTAL ASSIGNMENT OF THE B-11 NMR-SPECTRUM OF A PSEUDOCLOSO CARBAMETALLABORANE

The reaction between [(RhCl2(eta-C(9)Me(7)))(2)] and Tl-2[7-Ph-8-R-7,8 -nido-C2B9H9] (R = H or Ph) in CH2Cl2 afforded the heptamethylindenyl carbarhodaboranes 1-Ph-3-(eta-C(9)Me(7))-3,1,2-RhC2B9H10 1 and 1,2-Ph( 2)-3-(eta-C(9)Me(7))-3,1,2-RhC2B9H9 2, respectively, in good yields. T he B-11 NMR chemical shifts of 1 and 2 showed that they possess close and pseudocloso structures, respectively. Compound 1 was found to be f luctional in solution at room temperature via rotation of the Ph subst ituent, but cooling below ca. 230 K arrested this process, presumably by locking the indenyl ligand into its preferred cisoid conformation a nd preventing phenyl rotation. An X-ray diffraction study of a single crystal of 1 confirmed both the close nature of the cage and the cisoi d conformation, but additionally showed that, of two possible cisoid c onformations, the one adopted places the cage phenyl substituent under neath the six-membered ring of the indenyl group. Compound 2 was also subjected to crystallographic analysis, which confirmed the pseudoclos o nature of the cage. Again, the relative conformation of the two eta- bonded ligands is cisoid. An B-11-B-11 COSY spectrum of compound 2, th e first to be recorded from a pseudocloso species, allowed experimenta l assignment of the B-11 chemical shifts which were in excellent agree ment with those previously obtained theoretically.