Electrochemical and spectroelectrochemical investigation of Ru(por)(NO)(OAr) derivatives (por = octaethylporphyrin, tetraanisolylporphyrin; Ar = Ph, C6H4-2-NHC(O)CF3; C6H3-2,6-(NHC(O)CF3)2)

Abstract

The electrochemistry and spectroelectrochemistry of Ru(porphyrin)(NO)(phenoxide) complexes Ru(por)(NO)(OPh) (por = OEP, 1a; TAP, 2a; Ph = C₆H₅), Ru(por)(NO)(OAr¹) (por = OEP, 1b; TAP, 2b; OAr¹ = –OC₆H₄-(2-NHC(O)CF₃)), Ru(por)(NO)(OAr²) (por = OEP, 1c; TAP, 2c; OAr² = OC₆H₃-(2,6-NHC(O)CF₃)₂; OEP = octaethylporphyrinato dianion, TAP = tetraanisolylporphyrinato dianion) indicate that initial one-electron oxidation results in structure-dependent net reactivity at the phenoxide ligand. Oxidation of 1a generates 1a⁺, which undergoes a relatively slow rate-limiting second-order follow-up reaction. In contrast, 2a undergoes a diffusion-limited follow-up reaction after oxidation. Oxidation of species 1b and 2b results in dissociation of the corresponding phenoxide radicals from the metal center following a relatively slow first-order kinetic process. The ˙OAr¹ radical was detected by EPR spectroelectrochemistry. The follow-up reactions after oxidation of 1c and 2c are also very fast. In all cases, the ultimate fate of the ruthenium complex is to be trapped with adventitious water to generate the stable aqua complex. Further oxidation of each compound at higher potentials occurs at the porphyrin ligand, generating the π-radical cation observed by IR spectroelectrochemistry.