STERICALLY ENCUMBERED, CHARGE-COMPENSATED METALLACARBORANES - 18 - SYNTHESIS AND STRUCTURES OF RUTHENIUM PENTAMETHYLCYCLOPENTADIENYL DERIVATIVES

The reactions of [RuCl(Cp)]4 with monoanionic, charge-compensated car borane anions have been studied and products characterized by NMR spec troscopy (H-1 and B-11) and single-crystal X-ray diffraction, With [9- SMe2-7,8-nido-C2B9H10](-), the product is the expected species 3-(Cp) -4-SMe2-3,1,2-closo-RuC2B9H10, the structure of which reveals some evi dence for steric congestion between the Cp and SMe2 substituents, whi ch is characteristic of all of the compounds studied. Use of the carbo rane anion [7-Ph-9-SMe2-7,8-nido-C2B9H9](-) affords 1-Ph-3-(Cp)-7-SMe 2-3,1,2-closo-RuC2B9H9, in which the Ph and SMe2 cage substituents are separated by a {BH} unit. H-1 NMR spectroscopy of this compound revea ls restricted rotation of the phenyl group at room temperature. Moreov er, the compound isomerizes, slowly at room temperature but rapidly if warmed, to the C-cage-separated isomer 3-(Cp)-4-SMe2-11-Ph-3,1,2-clo so-RuC2B9H9. In contrast, and somewhat surprisingly, the analogous com pound 1-Ph-3-(Cp)-4-SMe2-3,1,2-closo-RuC2B9H9 (prepared from [RuCl(Cp )](4) and [7-Ph-11-SMe2-7,8-nido-C2B9H9](-)), which has adjacent Ph a nd SMe2 substituents, does not isomerize, even when heated, The reacti on between [RuCl(Cp)](4) and [7,8-Ph-2-9-SMe(2-)7,8-nido-C2B9H8](-) a ffords ,2-Ph-2-3-(Cp)-4-SMe2-3,1,2-pseudocloso-RuC2B9H8, the first ex ample of a charge-compensated pseudocloso metallacarborane.