Formation of [Mn(η-C5H5)O2] by photooxidation of [Mn(η5-C5H5)(CO)3] in low-temperature matrices containing O2

Abstract

The UV/VIS irradiation of [Mn(η⁵-C₅H₅)(CO)₃] in low-temperature matrices containing 25% O₂ led to the formation of a product A which, alongside absorptions assigned to a co-ordinated cyclopentadienyl ring, shows features in the IR spectrum at 938.0 and 893.0 cm^–1. On the basis of experiments involving isotopic substitution with ¹⁸O these bands are assigned respectively to ν_asym and ν_sym(O–Mn–O) vibrations of an MnO₂ unit. Species A is thus identified as the hitherto unknown organometallic oxide [Mn(η-C₅H₅)O₂] where the manganese atom is formally in the unusual +v oxidation state. The ¹⁶O–¹⁸O isotopic shift of ν_asym(MnO₂) of A gives an upper limit of 120 ± 8° for its O–Mn–O bond angle (θ). The intensity ratio of the bands arising from ν_sym and ν_asym(MnO₂) suggests a value of 110 ± 5° for the same angle.