Synthesis and Redox Chemistry of Octaethylporphyrin Complexes of Ruthenium(II) and Ruthenium(III)
Barley, M., Becker, J.Y., Domazetis, G., David Dolphin, and James, B.R.
Can. J. Chem.,
The syntheses and characterization of new octaethylporphyrin complexes Ru(OEP)(PBu3)2, Ru(OEP)(CO)L (L = PPh3, PBu3), [Ru(OEP)(PBu3)2]Br, and Ru(OEP)(PBu3)Br (OEP is the dianion of octaethylporphyrin) are described. Ru(OEP)(CO)EtOH (I) which reversibly loses the ethanol ligand in CH2Cl2 solution,undergoes a one-equivalent oxidation at the porphyrin ligand to generate the cation-radical [Ru(OEP) (CO)]+., a purple species of 2A2u ground state, produced electrochemically in perchlorate media, can coordinate bromide to generate a green 2A1u ground state species that also results from oxidation of I using bromine. Coordination of pyridine to [Ru(OEP) CO]+ yields the Ru(OEP) (CO)py species that can also be formed by electrochemical oxidation of Ru(OEP)(CO)py. Addition of tertiary phosphines (PR3) to the cation-radical carbonyl species can lead to [Ru(OEP)(PR3)2]+, via an internal electron transfer process from Ru(II) to the OEP+ that appears to be triggered by loss of the CO ligand. A reversible one-electron electrochemical oxidation of Ru(OEP)(PBu3)2 at 0.03 V (vs. Ag/AgCl) in CH2Cl2 also gives the ruthenium(III) biphosphine cation, while a further one-electron oxidation at 1.2 V generates [Ru(OEP) (PBu3)22+, a ruthenium(III) π-cation radical characterized by ESR. The [Ru(OEP)(PBu3)2]Br complex decomposes in the solid state to a mixture of Ru(OEP)(PBu3)Br, formed together with phosphine via an intramolecular ligand exchange, and Ru(OEP)(PBu3)2, formed by reduction of the initial ionic ruthenium(III) cation with the phosphine that appears as [PBu3Br]Br.