ratio of ca. 1:1, consistent with the presence of rac (1a) and meso (1b) diastereoisomers. Addition of MeOH to a CH2CI2 solution of the mixture of ligands 1a and 1b leads to selective crystallisation of the rac isomer 1a; in this way samples of 1a and 1b in purity of >95% are readily obtained.