Photochemical resolution of a thermally inert cyclometalated Ru(phbpy)(N-N)(sulfoxide)+ complex.

In this work a photosubstitution strategy is presented that can be used for the isolation of chiral organometallic complexes. A series of five cyclometalated complexes [Ru(phbpy)(N-N)(DMSO-κS)]+ ([1]PF6-[5]PF6) were synthesized and characterized, where Hphbpy = 6'-phenyl-2,2'-bipyridyl, and N-N = bpy (2,2'-bipyridine), phen (1,10-phenanthroline), dpq (pyrazino[2,3-f][1,10]phenanthroline), dppz (dipyrido[3,2-a:2',3'-c]phenazine, or dppn (benzo[i]dipyrido[3,2-a:2',3'-c]phenazine), respective-ly. Due to the asymmetry of the cyclometalated phbpy- ligand, the corresponding [Ru(phbpy)(N-N)(DMSO-κS)]+complexes are chiral. The exceptional thermal inertness of the Ru-S bond made chiral resolution of these complexes by thermal ligand exchange unrealistic. However, photosubstitution by visible light irradiation in acetonitrile was possible for three of the five complexes ([1]PF6-[3]PF6). Further thermal coordination of the chiral sulfoxide (R)-methyl p-tolylsulfoxide to the photo-product [Ru(phbpy)(phen)(NCMe)]PF6, followed by reverse phase HPLC, led to the separation and characterization of the two diastereoisomers of [Ru(phbpy)(phen)(MeSO(C7H7))]PF6, thus providing a new photochemical approach towards the synthesis of chiral cyclometalated ruthenium(II) complexes. Full photochemical, electrochemical, and frontier orbital charac-terization of the cyclometallated complexes [1]PF6-[5]PF6 was performed to explain why [4]PF6 and [5]PF6 are photochemi-cally inert, while [1]PF6-[3]PF6 perform selective photosubstitution.