Erratum to: Axial Imidazole Binding Strengths in Porphyrinoid Cobalt(III) Complexes as Studied by Tandem Mass Spectrometry

The Co(II) complexes of twelve meso-tetraaryl-porphyrins, -chlorins, and chlorin analogues containing non-pyrrolic heterocycles were synthesized and converted in situ to the corresponding Co(III) complexes coordinated to one or two imidazoles. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) in conjunction with the energy-variable collision-induced dissociation (CID) technique was used to compare the relative gas-phase binding strength of the axially coordinated imidazoles to the octahedral and square planar Co(III) porphyrinoid complex ions. The observed binding energies of these ligands were rationalized in terms of the effects of porphyrinoid core structure and meso-substitution on the electron density on the central Co(III) centers. Some of these trends were supported by DFT-based computational studies. The study highlights to which extend porphyrins vary from chlorins and chlorin analogues in their coordination abilities and to which extraordinary degree meso-thienyl-substituents influence the electronic structure of porphyrins. The study also defines further the scope and limits CID experiments can be used to interrogate the electronic structures of metalloporphyrin complexes.     

MS/MS Fragmentation Behavior Study of meso-Phenylporphyrinoids Containing Nonpyrrolic Heterocycles and meso-Thienyl-Substituted Porphyrins

Free base and cobalt(II) complexes of six meso-tetraphenylporphyrinoids containing nonpyrrolic heterocycles and of three meso-thienylporphyrins were investigated using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Their fragmentation was studied in a quadrupole ion trap as a function of the porphyrinoid macrocycle structure and compared with the fragmentation behavior of the benchmark compound meso-tetraphenylporphyrin. In situ oxidation of the neutral cobalt(II) complexes under ESI conditions produced singly charged cobalt(III) porphyrinoid ions; the free bases were ionized by protonation. For the porphyrinoids with an intact porphyrin core, the major fragmentation pathways observed were the losses of the meso-substituent (for meso-phenyl groups) and characteristic fragmentations of one or more meso-substituents (for the meso-thienyl group). Complex fragmentation pathways were observed for porphyrinoids with modifications to the porphyrin core but chemically reasonable structures could be assigned to most fragments, thus delineating general patterns for the behavior of pyrrole-modified porphyrins under CID conditions.

Complex Formation and Spectral Properties of meso-Phenyltetrabenzoporphyrins in Pyridine and N,N-Dimethylformamide

Contributions of structural (macroring distortion) and polarization (in asymmetrically substituted derivatives) effects into the reactivity and chromophoric properties of substituted porphyrins were revealed on the basis of the kinetics of complex formation of nona-, deca-, undeca-, and dodecasubstituted porphyrins (meso-phenyltetrabenzoporphyrins) with Zn(OAc)₂ in pyridine and the electronic absorption spectra of the ligands and their complexes with Zn(II) and Cu(II) in pyridine and N,N-dimethylformamide (DMF). Dodecaphenyl substitution produces a weaker ring distortion in the more aromatic tetrabenzoporphyrin compared with porphyrins themselves. Irrespective of the degree of macroring nonplanarity, the Zn (II) and Cu complexes of tetrabenzoporphyrins with increasing degree of meso-phenyl substitution meet a spectral stability criterion.     

Hydrogen chemical ionization mass spectrometry of metalloporphyrins

The hydrogen chemical ionization (H₂ CI) mass spectra of a range of metal(II) (Ni, Cu, Co, Pt), metal (III) (Al, Mn, Ga, Fe (bearing a single axial ligand)) and metal(IV) (Si, Ge, Sn (bearing two axial ligands) and V (as V?O²⁺)) porphyrins have been determined, The spectra are highly dependent on the coordinated metal, rather than the axial ligand(s) (where present). Ni(II), Cu(II), Mn(II or III), Ga(III), Ge(IV), Fe(III) and Sn(IV) porphyrins fragment via hydrogenation and demetallation, followed by cleavage of the resulting porphyrinogens at the meso(bridge) positions to give mono- and di-pyrrolic fragments. Tripyrrolic fragments are also observed in the case of Ni(II), Cu(II) and Sn(IV). Fragmentations of this type are similar to those observed for free-base porphyrins. In the case of Pt(II), Co(II), Al(III), Si(IV) and V(IV) (as vanadyl), the dipyrrolic fragment ions are either very weak or completely absent; hence their H₂CI spectra contain limited structural information. This variable CI behaviour may be related to the relative stabilities of the metalloporphyrins together with the multiple stable valency states exhibited by several metals.     

Imidazole and imidazolium porphyrins: gas‐phase chemistry of multicharged ions

Electrospray ionization mass spectrometry/mass spectrometry in the positive ion mode was used to investigate the gas‐phase chemistry of multicharged ions from solutions of porphyrins with 1,3‐dimethylimidazolium‐2‐yl (DMIM) and 1‐methylimidazol‐2‐yl (MIm) meso‐substituents. The studied compounds include two free bases and 12 complexes with transition metals (Cu(II), Zn(II), Mn(III), and Fe(III)). The observed multicharged ions are either preformed or formed during the electrospraying process by reduction or protonation and comprise closed‐shell and hypervalent mono‐radical and bi‐radical ions. The observed extensive and abundant fragmentation of the DMIM and MIm meso‐substituents is a characteristic feature of these porphyrins. Fragments with the same mass values can be lost from the meso‐substituents either as charged or neutral species and from closed‐shell and hypervalent radical ions. Reduction processes are observed for both the free bases and the metallated DMIM porphyrins and occur predominantly by formation of hypervalent radicals that fragment, at low energy collisions, by loss of methyl radicals with formation of the corresponding MIm functionalities. These findings confirm that, when using electrospray ionization, reduction is an important characteristic of cationic meso‐substituted tetrapyrrolic macrocycles, always occurring when delocalization of the formed hypervalent radicals is possible. For the Fe(III) and Mn(III) complexes, reduction of the metal centers is also observed as the predominant fragmentation of the corresponding reduced ions through losses of charged fragments testifies. The fragmentation of the closed‐shell ions formed by protonation of the MIm porphyrins mirrors the fragmentation of the closed‐shell ions of their DMIM counterparts. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermochemistry of Solution of Fe(III) and Mn(III) Complexes with Natural Porphyrins

The enthalpies of solution of Fe(III), Mn(III) complexes with porphyrins of the chlorophyllgroup (chlorophyll ligand, pheophorbid, chlorin e ₆) and protoporphyrin in various organic solvents at298.15 K were determined calorimetrically. The influence of the structural features of porphyrin molecules and nature of the solvent on the enthalpy characteristics of porphyrin-solvent interaction was discussed.     

Controlled porphyrinogen oxidation for the selective synthesis of meso-tetraarylchlorins

Chlorins have been synthesized through the reduction of the corresponding porphyrins although theoretically they can be obtained from reduced macrocycle forms as porphyrinogens. A new method for the oxidation of meso-tetraarylporphyrinogens was developed generating a substantial amount of chlorin relatively to porphyrin. The structure of the porphyrinogen, particularly the presence of substituents on the meso-phenyl groups, is decisive for the final yield of chlorin. In the case of meso-tetrakis(2,6-dichlorophenyl)porphyrinogen, 92% of the corresponding chlorin is obtained.     

The NMR spectra of the porphyrins. 17—Metalloporphyrins as diamagnetic shift reagents,structural and specificity studies

The nature of the metalloporphyrin-ligand complexes produced by zinc, magnesium and cobalt porphyrins with basic ligands has been investigated using the diamagnetic ring current shifts of the porphyrin on the ligand protons. The metal to nitrogen bond lengths in some metallo-meso-tetraphenylporphyrin (pyridine) complexes have been determined and compared with the data of the crystalline complexes. The geometry of the Zn meso-tetraphenylporphyrin complexes with 2-picoline, quinoline and isoquinoline has been investigated. Steric interactions between the ligand and the porphyrin in 2-picoline and quinoline produce a dramatic increase in the Zn? N bond length when compared to the unstrained analogues pyridine and isoquinoline. This large increase is associated with comparatively minor angle distortions in the complex. The specificity of the Zn meso-tetraphenylporphyrin complexation shifts has been determined for a range of benzyl and butyl compounds. The complexation shift is linearly related to the basicity of the ligand for a wide range of basicities.     

Specific Interaction of Nitrogen(II) Oxide with Sublimed Layers of Iron(II) meso-Mono-4-Pyridyltriphenylporphyrinate

IR studies revealed that unlike iron(II) meso-tetraphenylporphyrinate (FeTPP), NO interacts with sublimed layers of iron(II) meso-mono-4-pyridyltriphenylporphyrinate (FeM4PyTPP) to give two types of nitrosyl complexes. The stretching vibration frequency of the coordinated NO in one of them is close to that observed in the nitrosyl FeTPP complex, while in the other complex, it is 28 cm^–1lower. The spectral differences observed upon coordination of NO by two porphyrins with similar structures are explained by the fact that in the sublimed FeM4PyTPP layers, the structures are formed in which the pyridyl group of one molecule is coordinated by the metal ion of the neighboring molecule, while the nitrosyl ligand occupies the sixth coordination site. The thermal stability of the complexes formed, the effect of the extra ligands on the layer structure, and the mechanism of the nitrosyl ligand exchange for its isotopic analog ¹⁵NO are discussed.     

Chromium(III) and Chromium(IV) Tetraphenylporphine Complexes

Stable chromium complex (AcO)CrTPP was synthesized through the reaction of meso-tetraphenylporphine with chromium(III) acetate in boiling phenol. Coordination properties of chromium porphyrin in reaction with imidazole and pyridine in o-xylene were studied by electronic absorption spectroscopy and computer modeling. A single-electron oxidation of chromium(III) complex was found to be affected by peroxide compounds. The stability of an extra complex depends on the basic properties of the extra ligand and oxidation number of the central metal atom. The complex stability correlates with the calculated energy of formation of the metal–extra ligand bond. The geometrical structure and energy parameters of hexacoordinated chromium porphyrins were calculated using the quantum-chemical method. The effect of the cis and trans position of ligands in the composition of a macrocyclic compound was established to be significant only in the extra complexes (AcO)CrTPP.     

Porphyrin derivatives: Synthesis and potential applications

Porphyrin‐porphyrin and porphyrin‐chlorin dimers have been synthesized and evaluated for their photo‐physical and in vivo photodynamic therapy properties. Two of them can become potential new photosensitizers. Study of the reactivity of meso‐tetraaryl porphyrins, as dienophiles, in Diels‐Alder transformations and as dipolarophiles in 1,3‐dipolar cycloadditions, has been undertaken. New synthetic methodologies for certain chlorin, bacteriochlorin and isobacteriochlorin type macrocycles, with potential biological significance, have been established.     

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin,Chlorin, and Bacteriochlorin π‐Systems

Zinc complex of pyropheophorbide‐b, a derivative of chlorophyll‐b, was covalently dimerized through ethylene glycol diester. The synthetic homo‐dyad was axially ligated with two methanol molecules from the β‐face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto‐carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, ¹H NMR and IR spectra. All the synthetic zinc chlorin homo‐ and hetero‐dyads consisting of pyropheophorbides‐a, b and/or d took the above methanol‐locked and π–π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo‐dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo‐dyads partially took such supramolecules. The J‐type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads.     

Structural features of sublimed layers of meso-mono-4-pyridyltriphenylporphyrinatocobalt(ii) and reversible binding of molecular oxygen

The interaction of oxygen with sublimed layers of meso-monopyridyltriphenylporphyrinatocobalt(ii) (CoMPyTPP) was studied by electronic absorption and IR spectroscopy. The reversible binding of O₂ to the axial 5-position was shown for the freshly sublimed layers: the 6-position can either be free, or occupied by the pyridyl group of the adjacent molecule in the layer. The concentration of the complexes of the first type decreases to zero with time, whereas that of the second type complexes increases. The binding of oxygen on the sublimed layers of CoMPyTPP differs substantially from that on meso-tetraphenylporphyrinatocobalt(ii) and meso-tetra-3(4)-pyridylporphyrinatocobalt(ii), which loose their capability of O₂ binding with time.     

Synthesis of some 5,10,15,20-tetraalkylchlorin and tetraalkylporphyrin complexes of transition metals

Metal-assisted template syntheses of 5,10,15,20-tetraalkylchlorin and tetraalkylporphyrin complexes of transition metals are described. With Co only the porphyrins are obtained; with Cu only the chlorins; with Ni a mixture of chlorin and porphyrin is obtained depending on alkyl and added anhydride. As opposed to the higher alkyls, (5,10,15,20-tetramethylporphyrinato)nickel(II) dimerizes in solution, a dimerization constant of 3.9 ± 1.3 M^?1 being derived from ¹H nmr data.     

Synthesis of 2-Arylpyrimido[4,5-b]porphyrins via Cyclization Reaction with Ammonia

A facile synthetic strategy for the synthesis of a new series of β,β’-fused 2-arylpyrimido[4,5-b]porphyrins has been developed by using condensation cyclization reaction with ammonia. 2-Aroylamino-3-formylporphyrins were synthesized from 2-aroylaminoporphyrins under Vilsmeier–Haack reaction conditions, which were then efficiently converted to the corresponding 2-arylpyrimido[4,5-b]-5,10,15,20-tetrakis(4-chlorophenyl)-porphyrins via a condensation cyclization reaction. The nickel(II), copper(II), free-base and zinc(II) analogues of 2-arylpyrimido[4,5-b]porphyrins were successfully synthesized in 65–72 % yields and structurally characterized on the basis of spectral data analysis. On photophysical evaluation, 2-arylpyrimido[4,5-b]porphyrins demonstrated a 12–19 nm bathochromic shift in their electronic absorption spectra and up to 10 nm red shift in their emission spectra as compared to the simple meso-(tetrakis(4-chlorophenyl))porphyrins due to the extended π-conjugation.     

Energies of Charge Transfer for the Supramolecular Complexes of [60]- and [70]Fullerenes with a Series of meso-Tetraphenylporphyrins in the Solution State

Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (I _D ^V) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (E _A ^V) of [60]- and [70]fullerenes in solution. The value of E _A ^V for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes.     

meso‐Nitro‐ and meso‐Aminosubporphyrinatoboron(III)s and meso‐to‐meso Azosubporphyrinatoboron(III)s

meso‐Nitrosubporphyrinatoboron(III) was synthesized by nitration of meso‐free subporphyrin with AgNO₂/I₂. The subsequent reduction with a combination of NaBH₄ and Pd/C gave meso‐aminosubporphyrinatoboron(III). meso‐Nitro‐ and meso‐amino‐groups significantly influenced the electronic properties of subporphyrin, which has been confirmed by NMR and UV/Vis spectra, electrochemical analysis, and DFT calculations. Oxidation of meso‐aminosubporphyrinatoboron(III)s with PbO₂ cleanly gave meso‐to‐meso azosubporphyrinatoboron(III)s that exhibited almost coplanar conformations and large electronic interaction through the azo‐bridge.     

Energy-Minimized Structures and Calculated and Experimental Isomer Distributions in the Hexaaminecobalt(III) system [Co(trap)2]3+ (trap = 1,2,3-propanetriamine)

The two isomers of [Co(trap)₂]³⁺ (meso-[Co(trap)₂]³⁺ and rac-[Co(trap)₂]³⁺; trap = 1,2,3-propanetriamine) have been studied by strain-energy minimization. The two isomers have been separated preparatively by fractional crystallization, and fully characterized by ¹³C-NMR and electronic spectroscopy, and microanalyses. The calculated isomer distribution (rac/meso = 60%: 40%) is in good agreement with HPLC analysis of thermodynamic equilibrium mixtures at 298 K and 353 K (rac/meso = 55% : 45%). These results are discussed in relation to the approach of calculating isomer distributions of hexaaminecobalt(III) systems by strain-energy minimization neglecting the differences in environmental effects.     

Carbon Monoxide Coordination by Iron(II) meso-Mono-4-Pyridyltriphenylporphyrinate (FeM4PyTPP) and Its Structure in Sublimed Layers

Interaction of CO with sublimed layers of iron(II) meso-mono-4-pyridyltriphenylporphyrinate (FeM4PyTPP) resulting in the formation of known mono- and dicarbonyl complexes was studied using IR spectroscopy. The frequency of the stretching vibration of the coordinated CO in the monocarbonyl complex was found to be 20 cm^–1higher than in the complex with iron meso-tetraphenylporphyrinate (FeTPP), with the former complex being significantly more stable than the latter. The differences observed in CO coordination by porphyrins with close structures are explained by the formation, in the FeM4PyTPP sublimed layers, of oligomeric structures where the pyridyl group of one molecule is coordinated by the metal ion of the neighboring molecule. This conclusion is confirmed by a comparative analysis of IR spectra of FeM4PyTPP and FeTPP in the regions of structurally sensitive vibrations.     

Synthesis and characterization of cobalt(III) tetraaza macrocyclic complexes containing chloro and azido ligands

The complexes [Co(L)Cl₂]Cl · 4H₂O (1) and [Co(L)(N₃)₂]N₃ · 2H₂O (2) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0^1.18,0^7.12]docosane) have been synthesized, and structurally characterized by X-ray crystallography, spectroscopy and cyclic voltammetry. The crystal structure of (1) is centrosymmetric and the cobalt(III) atom has an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two chloride ligands. The cobalt(III) ion in (2) is coordinated to four nitrogen atoms from the macrocycle, and two azide ligands in an octahedral environment, which forms the 1D polymer through hydrogen bonding contacts involving the cation, azide anion and solvent water molecules. Electronic spectra of the complexes also exhibit a low-spin octahedral environment. Cyclic voltammetry of the complexes undergoes a one-electron wave corresponding to Co(III)/Co(II) processes. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the axial ligands.