Preparation, Characterization, Electrochemistry, and Infrared Spectroelectrochemistry of Ruthenium Nitrosyl Porphyrins Containing η ¹-O-Bonded Axial Carboxylates

The synthesis, characterization and redox behavior of eight low-spin nitrosyl carboxylate compounds (por)Ru(NO)[η¹-OC(=O)R] [por = T(p-OMe)PP: R = Me (1), iPr (2), tBu (3), p-C₆H₄NO₂ (4), Fc (5), CF₃ (8); por = TTP: R = Fc (6)] and [T(p-OMe)PP]Ru(NO)(OC₆HF₄) (7) are reported. The compounds are moderately stable in air as solids. Their IR (KBr) spectroscopic data show _NO's in the 1839-1861 cm^-1 range. The X-ray crystal structures of compounds 1, 2, 5-7, and 8 have been determined, and reveal linear RuNO linkages for these formally {RuNO}⁶ complexes. The redox behavior of the compounds at a Pt working electrode were studied in CH₂Cl₂ with NBu₄PF₆ as supporting electrolyte. The compounds display reversible first oxidations. IR spectroelectrochemistry of compounds 1-4, 7 and 8 revealed porphyrin-centered oxidations, whereas the ferrocenylcarboxylate compounds revealed first oxidations at the ferrocenyl moiety followed by second oxidations at the porphyrin macrocycles. Reductions of these compounds are accompanied by loss of the axial ligands. The redox behavior of a representative set of Ru porphyrin nitrosyls with η¹-O-carboxylate ligands reveal that the first oxidations occur at the porphyrin macrocycles. Appending redox-active ferrocenylcarboxylates to the (por)Ru(NO) centers alters the oxidation behavior such that the first oxidations occur on the ferrocenyl moieties. X-ray crystallographic data were obtained for six of these derivatives that show essentially linear RuNO linkages consistent with their {RuNO}⁶ descriptions.