Highly conjugated multiporphyrins: synthesis, spectroscopic and electrochemical properties

A series of meso-to-meso ethynyl-bridged multiporphyrin arrays have been synthesized using Sonogoshira palladium-catalyzed cross-coupling reactions involving the appropriate ethynylporphyrin and iodoporphyrin precursors. The absorption spectra of these multiporphyrins show splitting of the Soret bands and significant red shifts of the Q bands as compared to the combination of the corresponding components. These conjugated multiporphyrins also show red shifts in their emission spectra as the pi-conjugation is expanded. In the electrochemical measurements, the porphyrins dimer 7 shows two 1 - e- oxidations at E(1/2) = +0.63 and +0.76 V for the first electron abstraction from the two porphyrin rings, indicating electronic communication between the two porphyrin units. The porphyrin trimer 4 exhibits the first and second 1 - e- oxidations at E(1/2) = +0.68 and +0.77 V, respectively, which correspond to the two outer porphyrins. The cyclic voltammogram of pentamer 5 shows two overlapping 1 - e- couples at E(1/2) = +0.56 and +0.66 V, and one 2 - e- couple at E(1/2) = +0.86 V, for the four outer porphyrin units. These results demonstrate that in the porphyrin trimer and pentamer the individual peripheral porphyrin units are electrochemically coupled via a central porphyrin core. The UV-Vis-NIR spectra of the oxidized species of these multiporphyrins exhibit a broad intervalence charge transfer (IVCT) band in the region from 1200 to 3000 nm. The present work shows that a central porphyrin unit appended with ethynyl bridges affords strong electronic interactions between the peripheral porphyrin rings over a distance of about 15 A.     

Synthesis, properties, and crystal structure of a novel anthracene-bridged molybdenum-zinc porphyrin dimer

The synthesis and properties of novel anthracene-bridged porphyrin dimers having an oxomolybdenum(V) porphyrin unit, H(2)(DPA)[Mo(V)O(OMe)] (1) and (DPA)[Mo(V)O(OMe)][Zn(II)(MeOH)] (2), and the relevant monomer porphyrin complexes Mo(V)O(MPP)OMe (3) and Zn(II)(MPP) (4) are presented. An oxomolybdenum(V) unit was introduced into one of the two porphyrins in DPA to give 1, which has a free-base porphyrin unit. By introducing a zinc(II) ion to the free-base part, a mixed-metal complex of 2 was prepared and isolated. The structure of 2 was analyzed by X-ray crystallography (2.(7)/(6)CH(2)Cl(2), triclinic, P(-)1 (no. 2), a = 15.2854(12) A, b = 19.9640(15) A, c = 13.6915(12) A, alpha = 90.968(3), beta = 113.108(4), gamma = 96.501(4), Z = 2, R1 = 9.9, wR2 = 19.2). The structure of 2 demonstrated that a methanol is stably coordinated to the Zn(II) ion with the aid of a hydrogen bond to the methoxo ligand on the Mo(V) ion in the binding pocket of DPA. The electrochemical measurements of 2 suggested that the methanol was kept in the pocket of DPA in solution even at the reduced state of the molybdenum ion.     

Laser flash photolysis generation and kinetic studies of porphyrin-manganese-oxo intermediates. Rate constants for oxidations effected by porphyrin-Mn(V)-oxo species and apparent disproportionation equilibrium constants for porphyrin-Mn(IV)-oxo species

Porphyrin-manganese(V)-oxo and porphyrin-manganese(IV)-oxo species were produced in organic solvents by laser flash photolysis (LFP) of the corresponding porphyrin-manganese(III) perchlorate and chlorate complexes, respectively, permitting direct kinetic studies. The porphyrin systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPFPP), and 5,10,15,20-tetrakis(4-methylpyridinium)porphyrin (TMPyP). The order of reactivity for (porphyrin)Mn(V)(O) derivatives in self-decay reactions in acetonitrile and in oxidations of substrates was (TPFPP) > (TMPyP) > (TPP). Representative rate constants for reaction of (TPFPP)Mn(V)(O) in acetonitrile are k = 6.1 x 10(5) M(-1) s(-1) for cis-stilbene and k = 1.4 x 10(5) M(-1) s(-1) for diphenylmethane, and the kinetic isotope effect in oxidation of ethylbenzene and ethylbenzene-d(10) is k(H)/k(D) = 2.3. Competitive oxidation reactions conducted under catalytic conditions display approximately the same relative rate constants as were found in the LFP studies of (porphyrin)Mn(V)(O) derivatives. The apparent rate constants for reactions of (porphyrin)Mn(IV)(O) species show inverted reactivity order with (TPFPP) < (TMPyP) < (TPP) in reactions with cis-stilbene, triphenylamine, and triphenylphosphine. The inverted reactivity results because (porphyrin)Mn(IV)(O) disproportionates to (porphyrin)Mn(III)X and (porphyrin)Mn(V)(O), which is the primary oxidant, and the equilibrium constants for disproportionation of (porphyrin)Mn(IV)(O) are in the order (TPFPP) < (TMPyP) < (TPP). The fast comproportionation reaction of (TPFPP)Mn(V)(O) with (TPFPP)Mn(III)Cl to give (TPFPP)Mn(IV)(O) (k = 5 x 10(8) M(-1) s(-1)) and disproportionation reaction of (TPP)Mn(IV)(O) to give (TPP)Mn(V)(O) and (TPP)Mn(III)X (k approximately 2.5 x 10(9) M(-1) s(-1)) were observed. The relative populations of (porphyrin)Mn(V)(O) and (porphyrin)Mn(IV)(O) were determined from the ratios of observed rate constants for self-decay reactions in acetonitrile and oxidation reactions of cis-stilbene by the two oxo derivatives, and apparent disproportionation equilibrium constants for the three systems in acetonitrile were estimated. A model for oxidations under catalytic conditions is presented.     

A fluorinated ruthenium porphyrin as a potential photodynamic therapy agent: synthesis, characterization, DNA binding, and melanoma cell studies

When the new porphyrin 5,10-(4-pyridyl)-15,20-(pentafluorophenyl)porphyrin is reacted with 2 equiv of Ru(bipy)(2)Cl(2) (where bipy = 2,2'-bipyridine) formation of the target ruthenated porphyrin is achieved with 40% yield. Strong electronic transitions are observed in the visible region of the spectrum associated with the porphyrin Soret and four Q-bands. A shoulder at slightly higher energy than the Soret band is attributed to the Ru(dpi) to bipy(pi*) metal to ligand charge transfer (MLCT) band. The bipyridyl pi to pi* transition occurs at 295 nm. Cyclic voltammetry experiments reveal two single-electron redox couples in the cathodic region at E(1/2) = -0.80 and -1.18 V vs Ag/AgCl associated with the porphyrin. Two overlapping redox couples at E(1/2) = 0.83 V vs Ag/AgCl due to the Ru(III/II) centers is also observed. DNA titrations using calf thymus (CT) DNA and the ruthenium porphyrin give a K(b) = 7.6 x 10(5) M(-1) indicating a strong interaction between complex and DNA. When aqueous solutions of supercoiled DNA and ruthenium porphyrin are irradiated with visible light (energy lower than 400 nm), complete nicking of the DNA is observed. Cell studies show that the ruthenated porphyrin is more toxic to melanoma skin cells than to normal fibroblast cells. When irradiated with a 60 W tungsten lamp, the ruthenium porphyrin preferentially leads to apoptosis of the melanoma cells over the normal skin cells.     

Titrations in non-aqueous media: potentiometric investigation of symmetrical and unsymmetrical tetra-aryl porphyrins with 4-nitrophenyl and 4-aminophenyl substituents in nitrobenzene solvent

The basicity of the symmetrical and unsymmetrical tetraphenylporphyrins, namely 5,10,15,20-tetraphenylporphyrin (I) (references), 5-(4-nitrophenyl)-10,15,20-triphenylporphyrin (II), a mixture of 5,10-bis(4-nitrophenyl)-15,20-diphenylporphyrin and 5,15-bis(4-nitrophenyl)-10,20-diphenylporphyrin (III), 5,10,15-tris(4-nitrophenyl)-20-phenylporphyrin (IV), 5,10,15,20-tetrakis(4-nitrophenyl)porphyrin (V), 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (VI), a mixture of 5,10-bis(4-aminophenyl)-15,20-diphenylporphyrin and 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin (VII), 5,10,15-tris(4-aminophenyl)-20-phenylporphyrin (VIII) and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (IX), was investigated potentiometrically in nitrobenzene solvent. This investigation showed that these compounds are basic rather than acidic. Although they can not be titrated even with tetrabuthylammonium hydroxide, they can easily be titrated with perchloric acid to give well shaped and stoichiometric end-points. In addition they all undergo two proton reactions per porphyrin molecule. However, compounds VI, VII, VIII and IX each shows a second end-point to give three, four, five and six proton reactions, respectively, per porphyrin molecule. Half neutralization potentials (measures of their basicity) of these compounds are: I=368, II=409, III=432, IV=461, V=520, VI=340, VII=302, VIII=238 and IX=225 mV versus Ag/AgCl in methanol. These potentials clearly indicate that, if para-hydrogen with respect to the porphyrin core of tetraphenylporphyrin (I) is replaced with an acidifying nitro group (II, III, IV and V) the basicity of I decreases. This decrease is approximately proportional to the number of nitro groups. Each nitro group decreases the half neutralization potential by about 35 mV. On the other hand, if para-hydrogen indicated above is replaced with a basifying amino group (VI, VII, VIII and IX) the basicity increases. This increase is also approximately proportional to the number of amino groups. Each amino group increases the half neutralization potential by about 36.7 mV. The values 35 and 36.7 mV indicate that in nitrobenzene solvent the electron releasing power of an amino group to the porphyrin system is a little stronger than the electron withdrawing power of a nitro group from the porphyrin system. All these observations reveal that the nitrogen atoms at the core of the porphyrin molecules are strongly influenced by changes at the periphery of the molecules, which is a very good indication that the substituted phenyl groups and the cores of the porphyrins are nearly in the same plane.     

Physicochemical and photophysical studies on porphyrin-based donor-acceptor systems: effect of redox potentials on ultrafast electron-transfer dynamics

We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalently coupled to a redox active Mo center, MoL*(NO)Cl(X) (L* is the face-capping tridentate ligand tris(3,5-dimethylpyrazolyl) hydroborate and X is a phenoxide/pyridyl/amido derivative of porphyrin). The luminescence quantum yields of the bichromophoric systems (1, 2, and 5) were found to be an order of magnitude less than those of their respective porphyrin precursors. Transient absorption measurements revealed the formation of the porphyrin radical cation species (P(.)(+)) and photoinduced electron transfer from the porphyrin moiety to the respective Mo center in 1, 2, and 5. Electrochemical studies showed that the reduction potentials of the acceptor Mo centers in a newly synthesized pyridyl derivative (2; E(1/2)[Mo(I/0)] = approximately -1.4 V vs Ag/AgCl) and previously reported phenoxy- (1; E(1/2)[Mo(II/I)] = approximately -0.3 V vs Ag/AgCl) and amido- (3; E(1/2)[Mo(II/I)] = approximately -0.82 V vs Ag/AgCl) derivatives were varied over a wide range. Thus, studies with these complexes permitted us to correlate the probable effect of this potential gradient on the electron-transfer dynamics. Time-resolved absorption studies, following excitation at the Soret band of the porphyrin fragment in complexes 1, 2, and 5, established that forward electron transfer took place biexponentially from both S2 and S1 states of the porphyrin center to the Mo moiety with time constants 150-250 fs and 8-20 ps, respectively. In the case of MoL*(NO)ClX (where X is pyridine derivative 2), the high reduction potential for the MoI/0 couple allowed electron transfer solely from the S2 state of the porphyrin center. Time constants for the charge recombination process for all complexes were found to be 150-300 ps. Further, electrochemical and EPR studies with the trichromophoric complexes (3 and 4) revealed that the orthogonal orientation of the peripheral phenoxy/pyridyl rings negated the possibility of any electronic interaction between two paramagnetic Mo centers in the ground state and thereby the spin exchange, which otherwise was observed for related Mo complexes when two Mo centers are separated by a polyene system with comparable or larger separation distances.     

meso－5，10，15，20－四（3，4，5－三甲氧基苯基）卟啉的晶体和分子结构

用Ｘ－射线测定了ｍｅｓｏ－５，１０，１５，２０－四（３，４，５－三甲氧基苯基）卟啉的溶剂（正庚烷）合物（ＴＴＯＭＰＰ·２Ｃ＿７Ｈ＿（１６））的晶体结构。实验表明，该化合物（Ｃ＿（７０）Ｈ＿（８６）Ｎ＿４Ｏ＿（１２））的晶体属三斜晶系，空间群Ｐ１，ａ＝８．７４９（６），ｂ＝１５．１２９（６），ｃ＝１６．４４９（３），ａ＝６０．０７（３），β＝７０．６４（４），γ＝８１．７０（５），Ｖ＝１７７９．６，Ｍ＿ｒ＝１１７５．４９，Ｚ＝１，Ｄ＿ｃ＝１．０９７ｇ／ｃｍ￣３，μ＝０．６９７ｃｍ￣（－１），Ｆ（０００）＝６３０。讨论了卟啉环上取代基的电子和立体效应及卟啉与铁（Ⅲ）离子配位后铁（Ⅲ）离于对卟啉结构参数的影响。     

Unexpected stereodynamic consequences of the restricted rotations in ortho-acyl- and ortho-vinyl biphenyls

Surprisingly, the aryl-aryl rotation barriers of biphenyl derivatives ortho-substituted by the "small" HC=O and HC=CH2 groups (10.0 and 8.4 kcal mol-1, respectively) were found greater than those observed in biphenyls ortho-substituted by the "large" t-BuC=O and t-BuC=CH2 groups (6.7 and 6.9 kcal mol-1, respectively).     

水溶性锰卟啉体系催化氧化反应停流谱研究

采用快速混合停流技术,考察了pH=7.4,V(CH~3CN):V(H~2O)=1:1的混合溶剂中水溶性锰卟啉Mn^I^I^I(TMPyP)与单氧给体NaOCl及KHSO~5构建的细胞色素P-450模拟酶体系催化氧化活性物种的生成及催化烯烃DPBD环氧化过程。实验表明,在反应进行中存在着两种中间体：oxo-Mn^V(Por.)(1)和oxo-Mn^I^V(Por.)(2),但两者的催化活性有差异,在催化烯烃DPBD环氧化反应中,对于Mn^I^I^I(TMPyP)-NaOCl体系起催化作用的主要作用的主要是中间体1,而对于Mn^I^I^I(TNPyP)-KHSO~5体系两种中间体均与烯烃配位生成环氧化产物,并且该体系催化活性较高。     

Ni(III) complex of an N-confused porphyrin inner C-oxide

A novel, structurally characterized Ni(III) complex of an N-confused porphyrin inner C-oxide has been synthesized from the oxidation of a Ni(II) N-confused porphyrin using OsO4. Crystal data: C53H40N5NiO.CH2Cl2, monoclinic, space group P2/a (No. 13), a=21.229(1) A, b=8.6451(5) A, c=25.762(2) A, beta=93.004(3) degrees, V=4721.6(5) A3, and Z=4.     

Synthesis and characterization of alkanethiolate-coordinated iron porphyrins and their dioxygen adducts as models for the active center of cytochrome p450: direct evidence for hydrogen bonding to bound dioxygen.

Two kinds of novel cytochrome P450 models, which have alkanethiolate axial ligands and hydroxyl groups inside molecular cavities, were designed and synthesized as functional O(2) binding systems. A superstructured porphyrin, designated as "twin-coronet" porphyrin, was used as the common framework of the model complexes. This porphyrin bears four binaphthalene bridges on the both sides and forms two pockets surrounded by the bulky aromatic rings. Thiobenzyloxy and thioglycolate moieties, which contain an alkanethiolate group exhibiting various electron-donating abilities and degrees of bulkiness, were covalently linked to twin-coronet porphyrin to yield thiolate-coordinated hemes, TCP-TB and TCP-TG (twin-coronet porphyrin with thiobenzyloxy and thioglycolate groups), respectively. Both ferric complexes exhibited high stability during usual experimental manipulation under air and were characterized by MS, UV/vis, ESR spectroscopies, and CV. The ESR spectra exhibited low-spin signals (TCP-TB: g = 2.334, 2.210, 1.959; TCP-TG: g = 2.313, 2.209, 1.966). The cyclic voltammogram of TCP-TB in CH(3)CN gave a quasi-reversible wave which corresponds to the Fe(III)/Fe(II) redox couple: E(p)()(/2) = -1.35 V (vs Fc/Fc(+)). On the other hand, TCP-TG showed a fine reversible wave: E(1/2) (Fe(III)/Fe(II)) = -1.12 V. The stable dioxygen adducts were formed in the reaction of the ferric complexes with KO(2) under an oxygen atmosphere and characterized by UV/vis and resonance Raman (RR) spectroscopies. In the RR spectra, the nu(O--O) bands of the dioxygen adducts were observed at 1138 cm(-1) (TCP-TB) and 1137 cm(-1) (TCP-TG). The hypothesis that hydrogen bonding between the bound oxygen and the hydroxyl groups of the binaphthyl moieties could increase their stability was verified by RR spectroscopy. When all hydroxyl groups were deuterated, only the frequencies of the nu(O--O) bands were upshifted by 2 cm(-1) without any perturbation in the porphyrin skeleton. This work shows the first direct evidence for a hydrogen bond to dioxygen in an oxy form of a thiolate-coordinated heme model system. These results are discussed in context of the process of dioxygen binding and activation in cytochrome P450.     

Axial bis(terpyridoxy)phosphorus(V) porphyrin: modulation of PET and EET by Zn2+ or Cd2+ ions

A novel phosphorus(V) porphyrin bearing two ptp[4'-(4-phenyloxy)-2,2'ratio6',2'-terpyridine] groups was prepared and modulation of the intramolecular PET (lambda(ex)= 566 nm) and PET --> EET (lambda(ex)= 300 nm) processes was studied from ptp to phosphorus(V) porphyrin by Zn2+ or Cd2+ ions.     

水溶性锰卟啉模拟酶体系快速混合停流谱研究

采用快速混合停流技术,考察了不同pH值条件下水溶性锰卟啉MnⅢ(TMPyP)与四种单氧给体m CPBA、KHSO5、NaOCl及H2O2构建的细胞色素P 450模拟酶体系催化氧化活性物种的生成及催化烯烃环氧化过程.低pH值时,主要生成四价锰氧中间体2;而在高pH值时,首先生成五价锰氧中间体1,该中间体再向四价中间体2转化.     

CO2电催化还原的研究(Ⅲ)——TPP、TMAP、TMAPI系列金属卟啉的电催化活性

由于CO₂电催化还原有较高的电流效率、较低的过电位和较高的能量转换效率、因而倍受人们的注意。我们系统地研究了以TPP、TMAP和TMAPI为配体的配合物对CO₂电催化还原的活性,这对于开发CO₂的综合利用无疑是有意义的。     

Absorption spectroscopic and ESR studies on one-electron reduction products of copper(II) and oxovanadium(IV) tetraphenylporphyrins produced by γ-radiolysis in 2-methyltetrahydrofuran solutions at 77 K

Optical absorption spectra of one-electron reduced species of copper(II) and oxovanadium(IV) tetraphenylporphyrins. Cu(II)TPP and V(IV)OTPP, in 2-methyltetrahydrofuran at 77 K reveal that not the central metal but the porphyrin ligand is reduced by an excess electron. The triplet ESR spectrum resulting from the spin-spin interaction between two odd electrons located on the porphyrin ligand and the central metal is observed for the one-electron reduced species of V(IV)OTPP while not for that of Cu(II)TPP.     

Synthesis, Characterization, and Spectroelectrochemistry of Cobalt Porphyrins Containing Axially Bound Nitric Oxide

Several cobalt nitrosyl porphyrins of the form (T(p/m-X)PP)Co(NO) (p/m-X = p-OCH(3) (1), p-CH(3) (2), m-CH(3) (3), p-H (4), m-OCH(3) (5), p-OCF(3) (6), p-CF(3) (7), p-CN (8)) have been synthesized in 30-85% yields by reaction of the precursor cobalt porphyrin with nitric oxide. Compounds 1-7 were also prepared by reaction of the precursor cobalt porphyrin with nitrosonium tetrafluoroborate followed by reduction with cobaltocene. Compounds 1-8 have been characterized by elemental analysis, IR and (1)H NMR spectroscopy, mass spectrometry, and UV-vis spectrophotometry. They are diamagnetic and display nu(NO) bands in CH(2)Cl(2) between 1681 and 1695 cm(-)(1). The molecular structure of 1, determined by a single-crystal X-ray crystallographic analysis, reveals a Co-N-O angle of 119.6(4) degrees. Crystals of 1 are monoclinic, P2/c, with a = 15.052(1) ?, b = 9.390(1) ?, c = 16.274(2) ?, beta = 111.04(1) degrees, V = 2146.8(4) ?(3), Z = 2, T = 228(2) K, D(calcd) = 1.271 g cm(-)(3), and final R1 = 0.0599 (wR2 = 0.1567, GOF = 1.054) for 3330 "observed" reflections with I >/= 2sigma(I). Cyclic voltammetry studies in CH(2)Cl(2) reveal that compounds 1-7 undergo two reversible oxidations and two reversible reductions at low temperature. This is not the case for compound 8, which undergoes two reversible reductions but an irreversible oxidation due to adsorption of the oxidized product onto the electrode surface. Combined electrochemistry-infrared studies demonstrate that each of the compounds 1-7 undergoes a first oxidation at the porphyrin pi ring system and a first reduction at either the metal center or the nitrosyl axial ligand. The formulation for the singly oxidized products of compounds 1-7 as porphyrin pi-cation radicals was confirmed by the presence of bands in the 1289-1294 cm(-)(1) region (for compounds 1-5), which are diagnostic IR bands for generation of tetraarylporphyrin pi-cation radicals.     

"True" iron(V) and iron(VI) porphyrins: a first theoretical exploration

We present here a first theoretical characterization of iron(V) (S = (3)/(2)) and iron(VI) (S = 0) porphyrin intermediates. The Fe(V) calculations exhibit exceptionally narrow convergence radii and we believe that for this reason they have long eluded researchers working on high-valent iron intermediates. The Fe(V)-N(nitrido) bond distance in the DFT(PW91/TZP) optimized geometry of Fe(V)(P)(N) is 1.722 A, comparable to and slightly longer than the Fe(IV)-O bond distance of 1.684 A in Fe(IV)(P)(O) and the Fe(IV)-N(imido) bond distance of 1.698 A in Fe(IV)(P)(NH). In contrast, the Fe(VI)-N(nitrido) bond distances in [Fe(VI)(P)(N)](+) (S = 0) and Fe(VI)(P)(N)(F) (S = 0) are dramatically shorter, 1.508 and 1.533 A, respectively, consistent with the formal triple bond character of the Fe(VI)-N(nitrido) bond. The nitrido ligand appears to be uniquely capable of stabilizing a "true" Fe(V) center, in the sense defined in the paper. All three unpaired electrons in Fe(V)(P)(N) are completely localized on the Fe(V)-N(nitrido) axis, with the Fe and N gross atomic spin populations being 1.579 and 1.550, respectively. In contrast, an axial ligand set consisting of an oxide and a fluoride do not stabilize an Fe(V) ground state but favor an electronic structure best described as an Fe(IV)-oxo porphyrin pi-cation radical.     

Synthesis and structural studies of early transition metalloporphyrin complexes. 1. X-ray structures of meso-5,10,15,20 tetratolyl hafnium(IV) μ-dioxo dimer complex and meso-5,10,15,20 tetratolyl porphyrin vanadium(IV) oxo complex

Abstract

(TTP) hafnium dichloride, 1, where TTP = meso-5,10,15,20 tetratolyl porphyrin dianion, has been synthesized and spectroscopically characterized as a precursor to 2. Hydrolysis of 1 gives (TTP) hafnium μ-dioxo dimer, 2. (TTP) vanadium oxo complex, 3, can be obtained by hydrolysis of the corresponding chloro complex. Compound 2 has been characterized by spectroscopic and single crystal X-ray diffraction analyses. [(TTP)HfO]₂-toluene crystalizes in the space group C2/c, a = 31.906(6) Å, b = 16.864(3) Å, c = 19.180(4) Å, β = 117.52(3)°, V = 9152(3) ų, d_calcd = 1.369 g/cm³, Z = 8, 6029 unique observed reflections, final R = 0.077. The Hf atom is 1.02 Å from the plane of the porphyrin ring; Hf-O bond lengths are 2.1 Å. The hafnium atoms are 3.06(1) Å from each other and the average Hf-O-Hf angle is 94°. The porphyrin rings are 5.4° from being parallel and the distance between the centers of the porphyrin rings is ～ 5.1 Å. TTPVO·mesitylene, 3, crystallizes from mesitylene in the space group P1, a = 8.365(2), b = 10.320(3), c = 14.380(5) Å, α = 91.91(3), β = 91.44(3), γ = 108.26(2)°, V = 1177.2(6) ų, d_calcd = 1.27 g/cm³, Z = 1, 1851 observed unique reflections, final R = 0.069. The average V - N distance = 2.016 Å. The coordination geometry around the vanadium is distorted C_4V. The V = O group is disordered about the center of inversion. The vanadium atom resides 0.57 Å above the plane of the nitrogens. The (ring center) -V = O angle is 165.9° while the V = O vector is essentially colinear with the vector normal to the plane of nitrogens.     

Porphyrin Nanorods Modified Glassy Carbon Electrode for the Electrocatalysis of Dioxygen,Methanol and Hydrazine

Porphyrin nanorods (PNR) were prepared by ionic self‐assembly of two oppositely charged porphyrin molecules consisting of free base meso‐tetraphenylsulfonate porphyrin (H₄TPPS₄^2?) and meso‐tetra(N‐methyl‐4‐pyridyl) porphyrin (MTMePyP⁴⁺M=Sn, Mn, In, Co). These consist of H₄TPPS₄^2?? SnTMePyP⁴⁺, H₄TPPS₄^2?? CoTMePyP⁴⁺, H₄TPPS₄^2?? InTMePyP⁴⁺ and H₄TPPS₄^2?? MnTMePyP⁴⁺ porphyrin nanorods. The absorption spectra and transmission electron microscopic (TEM) images of these structures were obtained. These porphyrin nanostructures were used to modify a glassy carbon electrode for the electrocatalytic reduction of oxygen, and the oxidation of hydrazine and methanol at low pH. The cyclic voltammogram of PNR‐modified GCE in pH 2 buffer solution has five irreversible processes, two distinct reduction processes and three oxidation processes. The porphyrin nanorods modified GCE produce good responses especially towards oxygen reduction at ?0.50 V vs. Ag|AgCl (3 M KCl). The process of electrocatalytic oxidation of methanol using PNR‐modified GCE begins at 0.71 V vs. Ag|AgCl (3 M KCl). The electrochemical oxidation of hydrazine began at around 0.36 V on H₄TPPS₄^2?? SnTMePyP⁴⁺ modified GCE. The GCE modified with H₄TPPS₄^2?? CoTMePyP⁴⁺ H₄TPPS₄^2?? InTMePyP⁴⁺ and H₄TPPS₄^2?? MnTMePyP⁴⁺ porphyrin nanorods began oxidizing hydrazine at 0.54 V, 0.59 V and 0.56 V, respectively.     

Synthesis and Electrochemistry of Tetraphenylporphyrins Containing an Antimony-Carbon sigma-Bond

The following five antimony(V) tetraphenylporphyrins with sigma-bonded antimony-carbon bonds were synthesized: [(TPP)Sb(CH(3))(2)](+)PF(6)(-), [(TPP)Sb(OCH(3))(OH)](+)PF(6)(-), [(TPP)Sb(CH(3))(OH)](+)ClO(4)(-), [(TPP)Sb(CH(3))(OCH(3))](+)ClO(4)(-), and [(TPP)Sb(CH(3))(F)](+)PF(6)(-). Each compound is stable toward air and moisture and has a high melting point (>250 degrees C). The electrochemistry and spectroelectrochemistry of these sigma-bonded porphyrins were examined in benzonitrile or dichloromethane containing 0.1 M tetrabutylammonium perchlorate as supporting electrolyte and the data compared to those for three previously synthesized OEP derivatives containing similar sigma-bonded and/or anionic axial ligands. Each porphyrin shows two reversible reductions and up to a maximun of one oxidation within the potential window of the solvent. Spectroelectrochemical data indicate formation of a porphyrin pi anion radical upon the first reduction as do ESR spectra of the singly reduced species. However, a small amount of the Sb(III) porphyrin products may be generated via a chemical reaction following electron tranfer. An X-ray crystallographic analysis of [(TPP)Sb(CH(3))(F)](+)PF(6)(-) is also presented: monoclinic, space group C2/c, Z = 8, a = 24.068(5) ?, b = 19.456(4) ?, c = 18.745(3) ?, beta = 94.69(2) degrees, R = 0.056.