Optically active co-ordination compounds. Part 39. Resolutions and configurations of compounds containing the cis-bis(ethylenediamine)rhodium(III) moiety

Abstract

The racemic cations (±)[Rh(en)₂(C₂O₄)]⁺ and (±)[Rh(en)₂(NO₂)₂]⁺ have been resolved, using (+)[Co(edta)]^– as resolving agent. The pair of less-soluble diastereoisomers (–)[Co(en)₂(C₂O₄)](+)[Co(edta)] and (+)[ Rh(en)₂(C₂O₄)](+)[Co(edta)] are isomorphous: also isomorphous are (–)[Co(en)₂(NO₂)₂](+)[Co(edta)] and (+)[Rh(en)₂(NO₂)₂](+)[Co(edta)]. These isomorphisms define the stereochemistry of these two rhodium cations relative to their cobalt analogues. Since the latter have known absolute stereochemistries, the rhodium compounds may be assigned as D(–). The oxalatorhodium(III) compound as its chloride is shown to undergo spontaneous resolution. By various reactions, chiefly with protonic acids, the resolved oxalato-cation has been converted into optically active [Rh(en)₂X₂]⁺(X = Cl^–, Br^–, or [OH]^–). Chiroptical properties for all the new optically active cations are given.