Vibrational spectra of dioxygen adducts and oxo complexes of ruthenium tetraphenylporphine (RuTPP)

Abstract

Infrared (IR) and resonance Raman (RR) spectra of dioxygen adducts and oxo complexes of ruthenium tetraphenylporphine (RuTPP) are reported. When a thin film of RuTPP reacts with O 2 two dioxygen adducts are observed in the IR spectra. One is formed at ∼ 25 K and exhibits ν(OO) at 1124 cm −1 which shifts to 1114 cm −1 at 45 K. The second one is observed at slightly higher temperature (45 K) and its ν(OO) is located at ∼1167 cm −1. Both ν(OO) are down-shifted when a thin film is warmed up. The former dioxygen adduct is stable up to 270 K while the latter disappears at ∼ 100 K. On the other hand, the ν(OO) of these two dioxygen adducts are not observed in the RR spectra obtained in low temperature solution. Instead, the oxidation of RuTPP in toluene at ∼ 185 K yields the RuO 2Ru peroxo bridged dimer which exhibits the ν s(RuO 2) at 552 cm −1. When the temperature of the solution is gradually raised, the peroxo bridged dimer is transformed to TPPRu(IV)O which, in turn, is converted into TPPRu(VI)(O) 2. The ν(RuO) of the monooxo complex is expected to be at ∼820 cm −1 based on the ∼40 cm −1 up-shift upon 18O/ 16O isotopic substitution [ν(Ru 18O) is located at 780 cm −1] but is oscured by the strong porphyrin band at 826 cm −1. The ν s(ORuO) of the dioxo complex is observed at 811 cm −1 and is shifted to 767 cm −1 by 16O/ 18O isotopic substitution.