193353-62-7Relevant academic research and scientific papers
Paramagnetic ruthenium( III) cyclometallated complex. Synthesis, spectroscopic studies and electron-transfer properties
Hariram, Ramanathan,Santra, Bidyut Kumar,Lahiri, Goutam Kumar
, p. 155 - 163 (2007/10/03)
The reaction of RuII(PPh3)3X2 (X = Cl, Br) with o-(OH)C6H4C(H)=N-CH2C6H5 (HL) under aerobic conditions affords RuII(L)2(PPh3)2, 1, in which both the ligands (L) are bound to the metal center at the phenolic oxygen (deprotonated) and azomethine nitrogen and RuIII(L1)(L2)(PPh3), 2, in which one L is in bidentate N,O form like in complex 1 and the other ligand is in tridentate C,N,O mode where cyclometallation takes place from the ortho carbon atom (deprotonated) of the benzyl amine fragment. The complex 1 is unstable in solution, and undergoes spontaneous oxidative internal transformation to complex 2. In solid state upon heating, 1 initially converts to 2 quantitatively and further heating causes the rearrangement of complex 2 to the stable RuL3 complex. The presence of symmetry in the diamagnetic, electrically neutral complex 1 is confirmed by 1H and 31P NMR spectroscopy. It exhibits an RuII → L, MLCT transition at 460nm and a ligand based transition at 340nm. The complex 1 undergoes quasi-reversible ruthenium(II) -ruthenium(III) oxidation at 1.27V vs. SCE. The one-electron paramagnetic cyclometallated ruthenium(III) complex 2 displays an L → RuIII, LMCT transition at 658nm. The ligand based transition is observed to take place at 343nm. The complex 2 shows reversible ruthenium(III) - ruthenium(IV) oxidation at 0.875V and irreversible ruthenium(III) - ruthenium(II) reduction at -0.68V vs. SCE. It exhibits a rhombic EPR spectrum, that has been analysed to furnish values of axial (6560cm-1) and rhombic (5630cm-1) distortion parameters as well as the energies of the two expected ligand field transitions (3877cm-1 and 9540cm-1) within the t2 shell. One of the transitions has been experimentally observed in the predicted region (9090cm-1). The first order rate constants at different temperatures and the activation parameter ΔH# /ΔS# values of the conversion process of 1 → 2 have been determined spectrophotometrically in chloroform solution.
