Thermal and photo substitution reactivity and crystal structures of tridentate Schiff base–ruthenium(II) complexes containing phosphorus or sulfur donor atoms

Tridentate Schiff base–ruthenium(II) complexes containing soft phosphorus or sulfur donor atoms were prepared, and their bidirectional thermal and photo substitution reactions were investigated. In acetonitrile, the chloro ligands of trans(Cl,Cl)[RuCl2(ppb-etol)(PPh3)] (1, ppb-etol=2-(Ph2P)C6H4CHN(CH2)2OH) were substituted by acetonitrile molecules stepwise to yield [RuCl(CH3CN)(ppb-etol)(PPh3)]Cl (2) (first step) and [Ru(CH3CN)2(ppb-etol)(PPh3)]Cl2 (3) (second step). Complexes 2 and 3 reverted to complex 1 in acetonitrile upon irradiation with UV–Vis light. Similar thermal and photo substitution reactions were also observed for trans(Cl,Cl)[RuCl2(btb-etol)(PPh3)] (4, btb-etol=2-(tBuS)C6H4CHN(CH2)2OH). The substitution rates were measured for the first-step reactions of complexes 1 and 4 over the temperature range of 19.5–29.5 °C in acetonitrile. Kinetic parameters were determined to be kobsd=(1.13±0.04)×10−4 s−1 (25.0 °C), ΔH‡=83.1±1.7 kJ mol−1, and ΔS‡=−41.9±5.6 kJ mol−1 for complex 1, and kobsd=(1.57±0.06)×10−3 s−1 (25.0 °C), ΔH‡=88.8±1.9 kJ mol−1, and ΔS‡=−0.9±6.5 kJ mol−1 for complex 4. Accordingly, the substitution reaction of complex 4 proceeded faster than that of complex 1. The structures of [RuCl2{ppb-(1R,2S)-ephe}(PPh3)] (5, ppb-(1R,2S)-ephe=2-(Ph2P)C6H4CHNCH(Me)CH(Ph)OH), complex 2, and [Ru(CH3CN)2{ppb-(R)-btol}(PPh3)](BF4)2 (6, ppb-(R)-btol=2-(Ph2P)C6H4CHNCH(Et)CH2OH) were determined by X-ray analyses. In each complex, the geometry around the ruthenium atom is distorted octahedral, and the tridentate Schiff base and triphenylphosphine ligands occupy the equatorial positions.