Synthesis and characterization of a series of ruthenium(II) complexes with a tetraazapolyaromatic tridentate ligand dipyrido (2,3-a:3′,2′-j)phenazine

Abstract

A series of new mer-[Ru(dpop′)(N–N)Cl](PF6) (N–N=2,2-bipyrimidine (bpy); 1,10-phenanthroline (phen); 2,2′-bipyrimidine (bpm) and ethylenediamine (en)) complexes was prepared and the effect of N–N on physical properties of the complexes compared. The Ru dπ→dpop′ π∗ MLCT transition dominates the lower energy visible spectrum and increases in energy as N–N varies en<phen∼bpy<bpm. Ru dπ→N–N π∗ and intraligand π→π∗ transitions are observed at higher energy. Cyclic voltammetry results show increasingly stabilized Ru(II) dπ orbitals in the order of N–N variation en<phen∼bpy<bpm, consistent with en being exclusively a σ donor and bpm the most π∗ backbonding ligand. Spectro-electrochemical data show reversible one electron oxidative and reductive processes for all mer-[Ru(dpop′)(N–N)Cl]+ complexes except N–N=en. 1H; 13C and 2-D NMR data in CH3CN presented support the proposed structures. 1H NMR data was also used to verify the Cl− substitution in D2O. Aquation yields the mer-[Ru(dpop′)(N–N)(H2O)]+2 complexes with pseudo first order kinetics and the lability of Cl− follows a trend with the N–N group bpm<phen<bpy<en.