Separation and optical resolution of a pair of atrop diastereomers of the octahedral rhodium(III) complex with a nine-membered S,S-chelate ring.

Treatment of fac-[Rh(aet) 3] (aet = 2-aminoethanethiolate) with 2,2'-bis(bromomethyl)-1,1'-biphenyl gave a mononuclear rhodium(III) complex with a nine-membered S, S-chelate ring, fac-[Rh(aet)(L)] (2+) ([ 1] (2+), L = 2,2'-bis(2-aminoethylthiomethyl)-1,1'-biphenyl). Complex [ 1] (2+) afforded a pair of atrop diastereomers, Delta SS( S ax)/Lambda RR( R ax)-[ 1] (2+) ([ 1a] (2+)) and Delta SS( R ax)/Lambda RR( S ax)-[ 1] (2+) ([ 1b] (2+)), which involves the axial chirality ( R ax/ S ax) about a biphenyl moiety of L, besides the central chirality (Delta/Lambda) about a Rh (III) ion bound by two asymmetric ( R/ S) thioether donors. The atrop diastereomers ([ 1a] (2+) and [ 1b] (2+)) were successfully separated, isolated, and optically resolved, and the circular dichroism (CD) contribution from the axial chirality was evaluated by CD spectral analyses.