ABSTRACT
The reaction of Os(RL1)(PPh3)2(CO)Br, 1b, with qui-nolin-8-ol (HQ), 2, has furnished complexes of the type [Os(RL2)(PPh3)2(CO)(Q)], 3, in excellent yield (RL1 is C6H2O-2-CHNHC6H4R(p)-3-Me-5, RL2 is C6H2OH-2-CHNC6H4R(p)-3-Me-5 and R is Me, OMe, Cl). In this process, quinolin-8-olato (Q) undergoes five-membered chelation, the iminium-phenolato function tautomerizing to the imine-phenol function. The trans geometry of the Os(PPh3)2 fragment is consistent with the occurrence of a single 31P resonance near –6.0 ppm in 3. In dichloromethane solution, 3 displays a quasireversible 3+/3 couple near 0.40 V vs. SCE (3+ is the osmium (III) analogue of 3). Coulometrically generated solutions of 3+ displays a strong absorption near 340 nm, 415 nm and 500 nm and are one-electron paramagnetic (low-spin d5, S = 1/2) and show rhombic EPR spectra in 1:1 dichloromethanetoluene solution at 77 K with g values near 2.44, 2.20, 1.83. Distortion parameters using the observed g values have been computed. Solutions of 3 absorb near 420 nm and emit near 510 nm at 298 K and 580 nm at 77 K. The fluorescence is believed to originate from the 3MLCT state.