Crystallization-induced asymmetric transformation of chiral-at-metal ruthenium(II) complexes bearing achiral ligands

Recently, we observed that the enantiopure Lambda form of the tributylammonium salt of the chiral anion tristetrachlorobenzene-1,2-bis(olato)]phosphate, also named Trisphat, was able to induce an efficient resolution of a Delta,Lambda racemic mixture of cis-Ru(dmp)2(NCCH3)2](PF6)2 (dmp=2,9-dimethyl-1,10-phenanthroline) due to the spontaneous and selective precipitation of the heterochiral pair Delta-Ru(dmp)2(CH3CN)2]Lambda-Trisphat]2. We report here that the combination of such a stereoselective precipitation process and irradiation results in the quantitative conversion of the initial Ru(dmp)2(NCCH3)2]2+ racemate into only one of the two enantiomers. This is the first example in inorganic chemistry of an asymmetric transformation that leads to a chiral complex with no chiral ligand. Finally, three new racemic ruthenium bis(diimine) complexes, namely Ru(dmp)2(NCCH3)Py](PF6)2 (Py=pyridine), Ru(dmp)2(1,3-diaminopropane)](PF6)2, and Ru(dmp)2(ethylenediamine)](PF6)2 were synthesized. For all of them, crystallization-induced asymmetric transformation proved to be an efficient way of obtaining the corresponding optically active chiral-at-metal complexes in high yields and with excellent stereoselectivities.