Low-Temperature “1,2 → 1,7” Isomerization of Sterically Crowded Icosahedral <i>c</i><i>loso</i>-((2,3,8-η³):(5,6-η²)- Norbornadien-2-yl)rhodacarborane via the Formation of a Pseudocloso Intermediate. Molecular Structures of [3,3-((2,3,8-η³):(5,6-η²)-C₇H₇CH₂)-1,2-(4‘-MeC₆H₄)₂- 3,1,2-<i>p</i><i>seudocloso</i>-RhC₂B₉H₉] and 1,2 → 1,7 Isomerized Products

Abstract

The metalation reaction of the K+ salt of the carborane anion [7,8-(4‘-MeC6H4)2-7,8-nido-C2B9H10]- (1) with [((2,3,5,6-η4)-C7H7-2-CH2OH)RhCl]2 (2) in a solution of CHCl3 or C6H6 at ambient temperature produced two diastereomeric closo complexes, [2,2-((2,3,8-η3):(5,6-η2)-C7H7CH2)-1,8-(4‘-MeC6H4)2-2,1,8-closo-RhC2B9H9] (5 and 6), the products of the low-temperature “1,2 → 1,7” carbon atom isomerization of a (nonisolable) [3,3-((2,3,8-η3): (5,6-η2)-C7H7CH2)-1,2-(4‘-MeC6H4)2-3,1,2-closo-RhC2B9H9]. The overall architecture and stereochemistry of diastereomers 5 and 6 have been determined crystallographically. It has been established that the isomerization reaction proceeds through the intermediate pseudocloso type complex [3,3-((2,3,8-η3):(5,6-η2)-C7H7CH2)-1,2-(4‘-MeC6H4)2-3,1,2-pseudocloso-RhC2B9H9] (4), which was isolated and characterized by microanalysis, multinuclear NMR spectroscopy, and a single-crystal X-ray diffraction study.