R. Hariram et al., PARAMAGNETIC RUTHENIUM(III) CYCLOMETALATED COMPLEX - SYNTHESIS, SPECTROSCOPIC STUDIES AND ELECTRON-TRANSFER PROPERTIES, Journal of organometallic chemistry, 540(1-2), 1997, pp. 155-163
The reaction of Ru-II(PPh3)(3)X-2 (X = Cl, Br) with o-(OH)C6H4C(H)=N-C
H2C6H5 (HL) under aerobic conditions affords Ru-II(L)(2)(PPh3)(2), 1,
in which both the ligands (L) are bound to the metal center at the phe
nolic oxygen (deprotonated) and azomethine nitrogen and Ru-III(L-1)(L-
2)(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 cyclometallati
on 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 s
tate upon heating, 1 initially converts to 2 quantitatively and furthe
r heating causes the rearrangement of complex 2 to the stable Rut, com
plex. The presence of symmetry in the diamagnetic, electrically. neutr
al complex 1 is confirmed by H-1 and P-31 NMR spectroscopy. It exhibit
s an Ru-II-->L, MLCT transition at 460nm and a ligand based transition
at 340nm. The complex 1 undergoes quasi-reversible ruthenium(II)-rith
enium(III) oxidation at 1.27V vs. SCE. The one-electron paramagnetic c
yclometallated ruthenium(III) complex 2 displays an L --> Ru-III, LMCT
transition at 658 nm. The ligand based transition is observed to take
place at 343 nm. The complex 2 shows reversible ruthenium(III)-ruthen
ium(TV) oxidation at 0.875V and irreversible ruthenium(III)-ruthenium(
II) reduction at -0.68V vs. SCE. It exhibits a rhombic EPR spectrum, t
hat has been analysed to furnish values of axial (6560cm(-1)) and rhom
bic (5630cm(-1)) distortion parameters as well as the energies of the
two expected ligand field transitions (3877 cm(-1) and 9540 cm(-1)) wi
thin the t(2) shell. One of the transitions has been experimentally ob
served in the predicted region (9090 cm(-1)). The first order rate con
stants at different temperatures and the activation parameter Delta H-
#/Delta S-# values of the conversion process of 1 --> 2 have been dete
rmined spectrophotometrically in chloroform solution. (C) 1997 Elsevie
r Science S.A.