Dioxygen and nitric oxide complexes of rhodium porphyrins

Article abstract of DOI:10.1021/ic50223a067

(RhOEP)₂ (OEP = octaethylporphyrin) reacts with dioxygen to form RhOEP(O₂) (S = 1/2). which subsequently forms the μ-peroxo complex (RhOEP)₂O₂. EPR studies of RhOEP(O₂) and RhTPP(O₂) (TPP = tetraphenylporphyrin) and their 1:1 donor complexes are reported and compared with those of the cobalt analogues. (RhOEP)₂, RhOEP(H), and RhOEP(Cl) all react with nitric oxide to ultimately produce the same product, RhOEP(NO). The reactions of RhOEP(Cl) and RhTPP(Cl) with nitric oxide proceed through a metastable paramagnetic intermediate Rh(por)(Cl)(NO) (por = porphyrin), which from EPR and electronic spectral studies is formulated as containing a porphyrin π-cation radical unit with an ²A_1u ground state. RhOEP(NO)(Cl) associates to form a radical dimer (S = 1) with D = 5.17 × 10^-3 cm^-1 and E = 2.4 × 10^-4 cm^-1, but only monomeric RhTPP(NO)(Cl) is observed. Electrochemical studies of rhodium(III) porphyrins also support the porphyrin cation radical formulation for Rh(por)(NO)(Cl) complexes.