Complexes of (5,10,15-tri-X-phenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III) triphenylphosphine, (OMTXPC)Co(PPh(3)), where X = p-OCH3, p-CH3, p-Cl, m-Cl, m-F, o-Cl, o-F, or H, were synthesized and characterized in nonaqueous media using electrochemical, spectroelectrochemical, and EPR techniques. The o-Cl derivative exists as different atropisomers in solution, and a thermal interconversion between them was achieved at 338 K in toluene. Activation parameters (Delta S-double dagger, Delta H-double dagger) for interconversion between the atropisomers were obtained from H-1 NMR measurements and were similar in magnitude to values reported for ortho-substituted tetraphenylporphyrin derivatives. Formation constants for pyridine binding to the pentacoordinate cobalt(III) corroles in benzene were obtained from W-visible spectrophotometric measurements and ranged between 20 and 193 M(-1), with the exact value depending upon the specific electron-donating or electron-withdrawing group on the three phenyl rings of the complex. The redox potentials of (OMTXPC)Co(PPh(3)) also shift with the nature of the phenyl ring substituents, and linear free-energy relationships are observed. Each cobalt(III) derivative undergoes two one-electron reductions, the first of which involves a Co(III)/Co(II) conversion add concomitant loss of the bound PPh(3) ligand. Four one-electron oxidations; are also observed for the investigated compounds, and this contrasts with the oxidative properties of related cobalt(II) porphyrins which undergo a maximum of three one-electron oxidations under similar solution conditions. The first one-electron oxidation of each cobalt(III) corrole is metal-centered and results in formation of a Co(IV) corrole as ascertained by EPR spectroscopic characterization of the electrogenerated species.
Adamian, V., D'Souza, F., Licoccia, S., DI VONA, M.l., Tassoni, E., Paolesse, R., et al. (1995). Synthesis, characterization, and electrochemical behavior of (5,10,15-tri-X-phenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III) triphenylphosphine complexes, where X = p-OCH3, p-CH3, p-Cl, m-Cl, o-Cl, m-F, o-F, or H. INORGANIC CHEMISTRY, 34(3), 532-540 [10.1021/ic00107a003].
Synthesis, characterization, and electrochemical behavior of (5,10,15-tri-X-phenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III) triphenylphosphine complexes, where X = p-OCH3, p-CH3, p-Cl, m-Cl, o-Cl, m-F, o-F, or H
LICOCCIA, SILVIA;DI VONA, MARIA LUISA;PAOLESSE, ROBERTO;BOSCHI, TRISTANO;
1995-01-01
Abstract
Complexes of (5,10,15-tri-X-phenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III) triphenylphosphine, (OMTXPC)Co(PPh(3)), where X = p-OCH3, p-CH3, p-Cl, m-Cl, m-F, o-Cl, o-F, or H, were synthesized and characterized in nonaqueous media using electrochemical, spectroelectrochemical, and EPR techniques. The o-Cl derivative exists as different atropisomers in solution, and a thermal interconversion between them was achieved at 338 K in toluene. Activation parameters (Delta S-double dagger, Delta H-double dagger) for interconversion between the atropisomers were obtained from H-1 NMR measurements and were similar in magnitude to values reported for ortho-substituted tetraphenylporphyrin derivatives. Formation constants for pyridine binding to the pentacoordinate cobalt(III) corroles in benzene were obtained from W-visible spectrophotometric measurements and ranged between 20 and 193 M(-1), with the exact value depending upon the specific electron-donating or electron-withdrawing group on the three phenyl rings of the complex. The redox potentials of (OMTXPC)Co(PPh(3)) also shift with the nature of the phenyl ring substituents, and linear free-energy relationships are observed. Each cobalt(III) derivative undergoes two one-electron reductions, the first of which involves a Co(III)/Co(II) conversion add concomitant loss of the bound PPh(3) ligand. Four one-electron oxidations; are also observed for the investigated compounds, and this contrasts with the oxidative properties of related cobalt(II) porphyrins which undergo a maximum of three one-electron oxidations under similar solution conditions. The first one-electron oxidation of each cobalt(III) corrole is metal-centered and results in formation of a Co(IV) corrole as ascertained by EPR spectroscopic characterization of the electrogenerated species.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
