Weihua Zhu

Electrochemistry and catalytic properties for dioxygen reduction using ferrocene-substituted cobalt porphyrins

Cobalt porphyrins having 0-4 meso-substituted ferrocenyl groups were synthesized and examined as to their electrochemical properties in N,N-dimethylformamide (DMF) containing 0.1 M tetra-n-butylammonium perchlorate as a supporting electrolyte. The examined compounds are represented as (Fc)n(CH3Ph)(4-n)PorCo, where Por is a dianion of the substituted porphyrin, Fc and CH3Ph represent ferrocenyl and/or p-CH3C6H4 groups linked at the four meso-positions of the macrocycle, and n varies from 0 to 4. Each porphyrin undergoes two reversible one-electron reductions and two to six one-electron oxidations in DMF, with the exact number depending upon the number of Fc groups on the compound. The first electron addition is metal-centered to generate a Co(I) porphyrin. The second is porphyrin ring-centered and leads to formation of a Co(I) π-anion radical. The first oxidation of each Co(II) porphyrin is metal-centered to generate a Co(III) derivative under the given solution conditions. Each ferrocenyl substituent can also be oxidized by one electron, and this occurs at more positive potentials. Each compound was investigated as a catalyst for the electoreduction of dioxygen when adsorbed on a graphite electrode in 1.0 M HClO4. The number of electrons transferred (n) during the catalytic reduction was 2.0 for the three ferrocenyl substituted compounds, consistent with only H2O2 being produced as a product of the reaction. Most monomeric cobalt porphyrins exhibit n values between 2.6 and 3.1 under the same solution conditions, giving a mixture of H2O and H2O2 as a reduction product, although some monomeric porphyrins can give an n value of 4.0. Our results in the current study indicate that appending ferrocene groups directly to the meso positions of a porphyrin macrocycle will increase the selectivity of the oxygen reduction, resulting in formation of only H2O2 as a reaction product. This selectivity of the electrocatalytic oxygen reduction reaction is explained on the basis of steric hindrance by the ferrocene substituents which prevent dimerization.

Synthesis, Characterization, and Electrochemistry of the Manganese(I) Complexes of meso-Substituted [14]Tribenzotriphyrins(2.1.1)

Metalation of 6,13,20,21-tetraaryl-22H-[14]tribenzotriphyrins(2.1.1) (TriP, 1u2009a-d) with [Mn(CO)5 Br] provided Mn(I) tricarbonyl complexes of [14]tribenzotriphyrins(2.1.1) 2u2009a-d in 85-93u2009% yield. The complexes were characterized by mass spectrometry and UV/Vis absorption, IR, and NMR spectroscopy. Single-crystal X-ray analyses revealed that 2u2009b and 2u2009c adopt bowl-shaped conformations. The redox properties of [(TriP)Mn(I) (CO)3 ] (2u2009a-d) were studied by cyclic voltammetry. Each compound undergoes two reversible one-electron reductions to form a porphyrin π anion radical and a dianion in CH2 Cl2 . Two oxidation waves were observed, the first of which corresponds to a metal-centered electron-transfer process. The redox potentials of 2u2009a-d are consistent with the optical spectroscopic data and the relatively narrow HOMO-LUMO gaps that were predicted in DFT calculations. The optical spectra can be assigned by using Michls perimeter model. TDDFT calculations predict the presence of several metal-to-ligand charge-transfer bands in the L-band region between 500 and 700u2005nm.

Neo-N-confused Phlorins and Phlorinone: Rational Synthesis and Tunable Properties

By the acid-catalyzed [2 + 2] condensation, an unprecedented neo-N-confused phlorin (neo-NCphlorin 1) was successfully synthesized. By treating 1 with N-chlorosuccinimide, the corresponding chloro-substituted neo-NCphlorin (1-Cl) was obtained. The oxidization of 1 with FeCl3 afforded the neo-N-confused phlorinone (neo-NCphlorinone 2), which bears a relatively coplanar conformation, different from the highly distorted ones observed for 1 and 1-Cl. Notably, 2 shows striking long-wavelength absorption beyond 1300 nm upon addition of TBAF.

Facile synthesis, spectroscopic and electrochemical properties, and theoretical calculations of porphyrin dimers with a bridging amide-bonded xanthene moiety

A free base porphyrin dimer bridged by a flexible amide-bonded xanthene moiety and its binuclear zinc(II) complex zinc(II) complex were synthesized and characterized. Structural characterization by MS and 1H NMR spectroscopy confirmed the bridged porphyrin dimer structure. The properties of the dimers were characterized by IR, UV-visible absorption, fluorescence and magnetic circular dichroism (MCD) spectroscopy, and electrochemistry studies. Theoretical calculations were carried out to analyze the electronic structures of porphyrin dimers with a bridging amide-bonded xanthene moiety.

Regioselective Oxidative Ring Cleavage of a Phlorin Analogue: An Approach for Synthesizing Linear Tetrapyrroles

Oxidation of neo-N-confused phlorin 1 with excessive FeCl3 leads to regioselective ring opening, generating three linear tetrapyrroles, i.e., (10 Z,15 Z)-biladienone 2, (10 Z,15 E)-biladienone 3, and 19-methoxy (10 Z,15 E)-biladiene 4 with an overall yield of 88%. The coordination of these compounds with Zn(II) is affected by the inverted terminal pyrrolic unit, and the presence of the electron-withdrawing keto moiety. The structural identities were also clearly elucidated by the crystal structures of 3 and 4-Zn and were rationalized by DFT calculations.

Dimethyl 3,5-diethyl-1H-pyrrole-2,4-dicarboxyl­ate

The title pyrrole derivative, C12H17NO4, consists of a pyrrole ring with two diagonally attached methoxycarbonyl groups and two diagonally attached ethyl groups. The two carbonyl groups are approximately in the same plane as the pyrrole ring, making dihedral angles of 3.50u2005(19) and 6.70u2005(19)°. In the crystal, adjacent molecules are assembled into dimers in a head-to-head mode by pairs of intermolecular N—H⋯O hydrogen bonds.

Construction of mixed corrole–phthalocyanine europium triple-decker complexes involving meso-substituted trans-A2B-corrole

With the view to exploit novel rare-earth heteroleptic corrole–phthalocyanine triple-decker complexes towards their potential applications in the fields of information storage devices and nonlinear optical materials, three europium triple-decker complexes containing one meso-substituted trans-A2B-corrole and two phthalocyanine macrocycles have been designed and synthesized. The investigated compounds are represented as Eu2[Pc(OC4H9)8]2[Cor(p-R1Ph)2(p-R2Ph)], where Pc = phthalocyanine, Cor = corrole, (p-R1Ph) and (p-R2Ph) are the substituents on the 5,15-meso and 10-meso positions of the corrole macrocycle, respectively, R1 is H, and R2 is a CH3O, F or Cl substituent at the para-position of the meso-phenyl ring. These novel europium triple-decker complexes were characterized by spectroscopic and electrochemical techniques in nonaqueous media. Under excitation at 633 nm, a typical Raman marker band of the phthalocyanine dianions Pc2− is observed at 1505 cm−1, resulting from the coupling of the CC (pyrrole) and CN (aza group) stretchings. The UV-visible spectra and redox potentials of each triple-decker were analyzed as a function of the sum of the Hammett substituent constants for the para-substituents on the meso-phenyl rings of the corrole macrocycle.

Push–pull type manganese(III)corroles: Synthesis, electronic structures and tunable interactions with ctDNA

The synthesis of three low symmetry A2B type Mn(III)triarylcorroles with meso-aryl substituents that provide push–pull electron-donating and -withdrawing properties is reported. An analysis of the structure-property relationships for the optical and redox properties has been carried out through a comparison with the results of theoretical calculations. The results demonstrate that A2B type Mn(III)triarylcorroles interact strongly with cell-free circulating tumor deoxyribonucleic acid (ctDNA) in solution, and that the interaction constants are enhanced when a stronger electron-donating substituent is introduced at the 10-position of the meso-triarylcorrole ligand.

2-Ethyl 4-methyl 5-ethyl-3-methyl-1H-pyrrole-2,4-dicarboxyl­ate

The title pyrrole derivative compound, C12H17NO4, was synthesized from methyl 3-oxopentanoate by a Knorr-type reaction and contains a pyrrole ring to which two diagonal alkoxycarbonyl groups and two diagonal alkyl substituents are attached. The methylcarbonyl and ethylcarbonyl substituents are approximately co-planar with the pyrrole ring, making dihedral angles of 5.64u2005(2) and 3.44u2005(1)°, respectively. In the crystal, adjacent molecules are assembled by pairs of N—H⋯O hydrogen bonds into dimers in a head-to-head mode.