Synthesis and stereochemistry of diastereomeric closo-(pi,sigma-dicyclopentenyl)rhodacarboranes with the agostic C-H ... Rh bond

A series of diastereomeric closo-(eta (1,2)-dicyclopentenyl)rhodacarborane complexes with the agostic C-H . . . Rh bond were synthesized starting from mono-C-substituted anionic nido-carboranes [nido-7-R-7,8-C2B9H11](-). The resulting diastereomeric mixtures were separated into individual isomers by either crystallization or chromatography. The structures and the stereoche mistry of the diastereomeric complexes were studied in detail by H-1 and C- 13 NMR spectroscopy. The relative configurations of two key isomers were es tablished by X-ray diffraction analysis. The mechanism of the stereospecifi c formation of diastereomeric complexes is discussed.