Synthesis and electrochemistry of dialkylosmium-(IV) and -(V) porphyrins. Crystal structure of [Os(ttp)(CH2SiMe3)2][H2ttp = 5,10,15,20-tetra(p-tolyl)porphyrin]

Abstract

Reaction of [Os(por)O₂][por = 5,10,15,20-tetra(p-tolyl)porphyrinate (ttp) or 2,3,7,8,12,13,17,18-octaethylporphyrinate (oep)] with thionyl chloride gave [Os(por)Cl₂] in good yields. The dichloride compounds are paramagnetic with µ_effca.2.7 µ_B and display temperature-independent contact-shifted ¹H NMR spectra. Reaction of [Os(por)Cl₂] with an excess of LiR (R = Ph or Me₃SiCH₂) gave air-stable diamagnetic dialkyl compounds [Os(por)R₂]. The structure of [Os(ttp)(CH₂SiMe₃)₂] has been established by X-ray crystallography. Cyclic voltammograms of the diphenyl compounds exhibit reversible metal-centred Os^V–Os^IV and Os^IV–Os^III couples. Treatment of [Os(ttp)Ph₂] with Ce^IV or AgBF₄ afforded the diphenylosmium(V) compound [Os(ttp)Ph₂]BF₄, which is paramagnetic with µ_effca. 1.7 µ_B.