Jianguo Shao

Spectroelectrochemical and ESR studies of highly substituted copper corroles

Electrochemical and spectroelectrochemical studies are presented for nine copper corroles with electron-withdrawing or electron-donating substituents on the three meso-phenyl rings of the compounds or on the eight β-pyrrole positions of the macrocycle. Up to three reversible oxidations can be seen for each Cu(III) corrole in CH2Cl2 containing 0.1 M TBAP. Unlike the case of (OEC)Cu, no dimer is electrochemically detected upon the first oxidation of these compounds at room temperature. However, a dimer forms at low temperature (< -50°C) for compounds having strong electron-donating groups. Two reductions are observed for all nine corroles at low temperature in CH2Cl2, 0.1 M TBAP, but only one reduction is detected at room temperature for four of these compounds which have weak electron-withdrawing or electron-donating groups. The neutral, reduced or oxidized Cu corroles were also characterized by thin-layer UV-visible spectroelectrochemistry and ESR. The resulting data indicates that eight of the nine neutr...

Solvent, Anion, and Structural Effects on the Redox Potentials and UV−visible Spectral Properties of Mononuclear Manganese Corroles

A series of manganese(III) corroles were investigated as to their electrochemistry and spectroelectrochemistry in nonaqueous solvents. Up to three oxidations and one reduction were obtained for each complex depending on the solvents. The main compound discussed in this paper is the meso-substituted manganese corrole, (Mes 2PhCor)Mn, and the main points are how changes in axially coordinated anion and solvent will affect the redox potentials and UV-vis spectra of each electrogenerated species in oxidation states of Mn(III), Mn(IV), or Mn(II). The anions OAc (-), Cl (-), CN (-), and SCN (-) were found to form five-coordinate complexes with the neutral Mn(III) corrole while two OH (-) or F (-) anions were shown to bind axially in a stepwise addition to give the five- and six-coordinate complexes in nonaqueous media. In each case, complexation with one or two anionic axial ligands led to an easier oxidation and a harder reduction as compared to the uncomplexed four-coordinate species.

Free-base corroles: determination of deprotonation constants in non-aqueous media

A series of free-base corroles with different electron-donating or electron-withdrawing substituents were reacted with piperidine, 4-aminopyridine, 2-methylimidazole, 2-aminopyridine or pyridine in PhCN and the UV-visible spectral changes monitored during conversion of (Cor)H3 to [(Cor)H2]- as a function of the concentration and strength of the added organic base. Analysis of the UV-visible spectral changes as a function of the added base concentration enabled calculation of equilibrium constants (logK) for deprotonation of each corrole under the given experimental conditions. Relationships are examined between the experimentally measured logK values and previously published spectroscopic and structural properties of the compounds.

β-Pyrrole brominated meso-tetraphenylporphyrins: synthesis, spectral and electrochemical properties

The synthesis, catalytic properties, UV-visible spectra and electrochemistry of β-pyrrole brominated porphyrins are summarized in this brief review. The effect of the Br substituents of the porphyrin ring on the redox behavior, and on axial CO or pyridine binding to the porphyrins is also discussed.

Control of the site and potential of reduction and oxidation processes in π-expanded quinoxalinoporphyrins

Quinoxalino[2,3-b]porphyrins are pi-expanded porphyrins, having a quinoxaline fused to a beta,beta-pyrrolic position of the porphyrin. They are used as components in systems proposed as molecular wires. Knowledge of their redox properties is of value in the design of electron- or hole-conduction systems. In particular, the location of the charge density in the radical anions of quinoxalinoporphyrins can be modulated by peripheral functionalization. New theoretical treatments of electrochemical potentials are developed that identify the site of reduction in both the anions and the dianions of 33 quinoxalinoporphyrins. These molecules include free-base and metallated macrocycles substituted on the quinoxaline with electron-withdrawing groups (NO2, Cl, Br) and/or electron-donating groups (NH2, OCH3). Spectroelectrochemistry, density-functional theory calculations, and substituent-parameter models are used to verify the analysis. Five distinct patterns are observed for the locations of the first and second reductions; some of these patterns involve delocalized charges. Nitroquinoxalinoporphyrins with the nitro groups at the 5- and 6-quinoxaline positions are found to have quite different properties owing to distortions caused by peri interactions that force the nitro group of the 5-nitro regioisomer out of conjugation. Charge localization on the nitroquinoxaline fragment is found for some molecules, and this is attributed to ion-pairing with the 0.1 M tetrabutylammonium perchlorate electrolyte used, leading to the verified prediction that electron-paramagnetic resonance spectra of these molecules taken without the electrolyte yield delocalized anions. These properties enable the control of conduction through molecular wires synthesised from quinoxalinoporphyrins.

Synthesis, physicochemical and electrochemical properties of metal–metal bonded ruthenium corrole homodimers

Abstract Two diruthenium(III,III) corrole dimers, [(Et 6 Me 2 Cor)Ru] 2 and [(Me 6 Et 2 Cor)Ru] 2 , where Et 6 Me 2 Cor and Me 6 Et 2 Cor are the 2,3,8,12,17,18-hexaethyl-7,13-dimethylcorrole and 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole trianions, respectively, were synthesized and characterized as to their spectroscopic and electrochemical properties. They exhibit up to three oxidations and two reductions by cyclic voltammetry in CH 2 Cl 2 or pyridine containing 0.1 M TBAP, almost all of which are electrochemically reversible on the voltammetric and/or thin-layer spectroelectrochemical timescale. The two reductions and the first two oxidations involve one-electron transfer processes which are separated from each other by 770–880 mV upon reduction and by 350–420 mV upon oxidation. The UV–vis spectroelectrochemical data suggest that the first two one-electron oxidations occur at the diruthenium metal centers while the third oxidation (seen only in CH 2 Cl 2 ) is proposed to be macrocycle-based, leading to the formation of a Ru 2 (IV,IV) corrole species. The formation of a Ru(III,IV) complex after abstraction of one electron is also suggested by the rhombic ESR spectrum of singly oxidized [(Me 6 Et 2 Cor)Ru] 2 at 77 K. The first one-electron reduction is also assigned as metal-centered and leads to the formation of a Ru 2 (III,II) complex. Finally, a comparison of electrochemical properties between the investigated diruthenium(III,III) corroles and an earlier characterized diruthenium(II,II) octaethylporphyrin, [(OEP)Ru] 2 , is presented.

Synthesis, spectral and electrochemical characterization of non-aggregating α-substituted vanadium(IV)-oxo phthalocyanines

Two α-substituted vanadium-oxo phthalocyanines, [(OC6H3(t-Bu)2)4Pc]VO and [(OC8H17)4Pc]VO, where OC6H3(t-Bu)2 is 2,4-di-tert-butylphenoxy and OC8H17 is 2,2,4-tri-methyl-3-pentoxy, were synthesized and characterized by elemental analysis, mass spectrometry, UV-visible, IR, ESR spectroscopy and electrochemistry. Both complexes have good solubility and do not aggregate in polar or non-polar solvents. Three reductions and two oxidations can be observed in DMF containing 0.2 M TBAP. A HOMO-LUMO gap of ~1.4 V is seen for both complexes. The first two one-electron reductions and first oxidation are reversible diffusion controlled electrode processes under the given experimental conditions. The effects of solvent and phthalocyanine macrocycle substituents on the Q bands of the electronic absorption spectra are discussed.

Evidence that gold(III) porphyrins are not electrochemically inert: facile generation of gold(II) 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin

Gold(III) porphyrin 1 is shown to undergo reduction at the central metal ion to give the first known gold(II) porphyrin overturning the long held assumption that reduction of such complexes only occurs at the macrocycle.

Synthesis and characterization of highly soluble hexadecachloro- and hexadecafluorophthalocyanine ruthenium(II) complexes

A new synthesis is reported for hexadecafluorophthalocyanineruthenium(II), F16Pc(2-)RuII and hexadecachlorophthalocyanineruthenium(II), Cl16Pc(2-)RuII, is reported for the first time. These paramagnetic species, which contain no axial ligand, are quite reasonably soluble in a range of common organic solvents. We report and discuss electronic and vibrational (infrared and resonance Raman) spectroscopic, MALDI-TOF and magnetic data. In addition we report electrochemical data and use spectroelectrochemical methods to obtain the electronic spectra of these species in the phthalocyanine(1-), (3-) and (4-) oxidation states.

Synthesis and electrochemical investigation of covalently linked porphyrin dimers containing a β-brominated subunit.

Ten meso-tetraphenylporphyrin-type heterodimers containing a partly or completely β-brominated subunit were synthesized and characterized by UV-visible spectroscopy, cyclic voltammetry and spectroelectrochemistry, showing the presence of low electronic interactions between the two subunits. The investigated compounds are represented as M[(tripp-tpp(Br4)]M and M[tripp-tpp(Br8)]M(M = 2H, Zn, Ni, Co and Cu) where tripp-tpp(Br4) is the tetraanion of 1-[5-(10,15,20-triphenylporphyrinyl)]-4-[10-(2,3,12,13-tetrabromoporphyrinyl)]-benzene and tripp-tpp(Br8) is the tetraanion of 1-[5-(10,15,20-triphenylporphyrinyl)]-4-[10-(2,3,7,8,12,13,17,18-octabromoporphyrinyl)]-benzene. One of the synthesized dimers, H2[tripp-tpp(Br8)]H2, was characterized by a single-crystal X-ray investigation.