Synthesis and Characterization of Push-Pull Porphyrins

A series of “push-pull” porphyrins with 4-nitrophenyl and 4-aminophenyl substituents were synthesized and separated by flash column chromatographic techniques. They were fully characterized by elemental analysis, FAB-MS, FTIR, UV-visible, and ¹H NMR spectroscopies. The unsymmetrical π-electron distribution of the porphyrins caused by the donor (amino) and acceptor (nitro) substituents were investigated by ¹H NMR technique. The pyrrole-H resonance positions can be correlated to the Hammett σ constants of the substituents. Although with strong donor and acceptor substituents, UV-visible spectra show the push-pull porphyrins have rather weak solvatochromism and hence limited intramolecular charge-transfer character.     

5,15-二(对-取代苯基)八烷基卟啉及其金属配合物的合成

本文报道了五种5,15-二(对-取代苯基)-2,8,12,18-四乙基-3,7,13,17-四甲基卟啉(Ⅱa—Ⅱe)和五种5,15-二(对-取代苯基)-2,3,7,8,12,13,17,18-八甲基卟啉(Ⅰa—Ⅰe)以及它们的铜、铁、镍金属配合物的合成。这些化合物的结构均经元素分析、UV、~1HNMR和MS鉴定。芳环上不同取代基对卟啉成环反应有一定影响,拉电子基团有利于反应。其顺序如下:NO_2>H>CH_3>OCH_3>N(CH_3)_2。     

Preparation, electrochemical and spectral properties of N-methyl-pyridylethynyl nickel porphyrins

A series of nickel N-methyl-pyridylethynylporphines were synthesized and their electrochemical and absorption properties were studied. UV-visible spectra of these complexes show that the absorption red-shifts of the nickel porphyrins are as significant as the zinc analogues. Although the reduction potential shifts caused by the electron-withdrawing substituents are not as large as the zinc complexes, the first reduction potentials of the nickel porphyrins are more positive than those of the zinc counterparts. In addition, the redox behaviors of these nickel porphyrins are similar to those of the zinc analogues.     

Conformational landscape of meso-(1,3-dithian-2-yl)porphyrins

An investigation of the conformational landscape of 1,3-dithian-2-yl bearing porphyrins and the rotational behavior of the dithianyl substituents in meso position was carried out by variable-temperature (VT) NMR spectroscopy. Additionally, theoretical results for alternative conformations and energy barriers were obtained by molecular modeling. The study revealed different NH trans tautomers with regard to the orientation of the dithianyl ligands for the free base porphyrins 1-3. Relatively ruffled porphyrin core conformations were established for the transition states of the dithianyl rotation, resulting in a lower rotational energy barrier for the nickel(II) complex 4 compared to that of the free base systems. The data obtained and the first depiction of a rotational transition state for the rotation of bulky meso-alkyl substituents illustrate the close structural interplay between meso-alkyl substituents and the macrocycle conformation in porphyrins.     

Synthesis of β-pyrrole and β-thiophene substituted 21,23-dithia and 21-monothiaporphyrins

A series of β-pyrrole and β-thiophene substituted porphyrins with N₂S₂ and N₃S porphyrin cores were synthesized and characterized. The introduction of substituents at β-pyrrole and β-thiophene carbons resulted in significant shifts in ¹H NMR, absorption and fluorescence maxima. These effects were attributed to alteration of the porphyrin ring current caused by substituents at β-positions.     

Synthesis and conformational studies of chiral meso-(α,β-unsaturated)-porphyrins

We describe a method to improve the yield and the kinetics of the difficult syntheses of α,β-unsaturated porphyrins, which enabled us to obtain a new chiral porphyrin derived from (S)-(−)-perillaldehyde in a 6% yield. Variable temperature NMR experiments on the free base, the zinc(II) and the nickel(II) complexes showed that two distinct and consecutive dynamic processes linked with the meso substituents rotation occurred. These processes can be analyzed as an evolution of the conformer composition upon temperature change. Higher values are found for the free energies of rotation of the substituent (measured by variable temperature ¹H NMR) compared to those of other equivalent porphyrins like meso-tetraphenyl porphyrin or meso-tetracyclohexyl porphyrin.     

Mass spectrometry differentiation of isomeric alkyl porphyrins. Fragmentation analysis of meso-tetraoxoporphyrinogens

The mass spectra of lead dioxide oxidation products of three etiotype porphyrins and one meso-substituted etiotype porphyrin have been analyzed. The meso-tetraoxo products formed, fragment upon electron-impact to give mono-, di-, and tri-pyrrole fragments with the pyrrole substituents still intact. From this fragment information it is possible to differentiate many isomeric alkyl porphyrins. Due to the inability to assign exact positions to the substituents on each pyrrole unit, however, definite isomeric identification is impossible without further information. High resolution gas chromatography retension data of volatile (trimethylsiloxy) Si^IV derivatives may eventually provide the necessary additional information to make absolute structural assignment possible. The described method has been designed to prove detailed structural information about geoporphyrin materials. Geochemical conclusions from such data should help provide information about the origin of organic materials and thus help establish possible connections with early life processes.     

Direct Amination of meso‐Tetraarylporphyrin Derivatives – Easy Route to A3B‐, A2BC‐, and A2B2‐Type Porphyrins Bearing Two Nitrogen‐Containing Substituents at the meso‐Positioned Phenyl Groups

meso‐Tetraarylporphyrinato complexes 1a – g (Zn^II, Cu^II, and Ni^II) bearing one or two nitro‐substituted aryl moieties react with 1,1,1‐trimethylhydrazinium iodide in the presence of ^tBuOK in THF at 0–5° or in the presence of KOH in DMSO at 60–70° according to a nucleophilic substitution of an H‐atom, thus affording porphyrins 2a – g and 3f , g with amino‐functionalized meso‐positioned aryl substituents in yields up to 73% (Scheme 1 and Table). The products obtained are attractive intermediates for further derivatization of porphyrins and may be of potential use as sensitizers in photodynamic cancer therapy.     

Conversion of Ni(II)-allylporphyrins to alpha,beta-unsaturated formylporphyrins via a nickel-promoted reaction

A new route to alpha,beta-unsaturated formylporphyrins begins with the synthesis of allyl-substituted porphyrins via the Suzuki cross-coupling reaction of bromoporphyrins and allylboronic acid pinacol ester in 50-95% yield. Treatment of allyl-substituted porphyrins with nickel acetate in N,N-dimethylformamide (DMF) then affords mono- and diacroleinylporphyrins in up to 70% yield.     

Synthesis of 3-aryl-4-chalcogen-2H-benzopyrans from 3-iodo-4-chalcogen-2H-benzopyrans using a Suzuki cross-coupling

The Suzuki cross-coupling reaction of 3-iodo-4-chalcogen-2H-benzopyran derivatives with a variety of organoboron compounds in the presence of catalytic amount of palladium salt is described. This cross-coupling reaction proceeded cleanly and was performed with aryl boronic acids bearing electron-withdrawing, electron-donating, and neutral substituents, furnishing the corresponding products in moderate to good yields.     

THE EFFECTS OF PERIPHERAL SUBSTITUENTS ON THE KINETICS OF ZINC ION INCORPORATION AND ACID CATALYZED REMOVAL FROM WATER SOLUBLE SULFONATED PORPHYRINS

Abstract

The kinetics of Zn²⁺ and Zn(OH)⁺ incorporation into and the kinetics of the acid catalyzed removal of Zn(II) from twelve water-soluble, sulfonated derivatives of tetraphenylporphyrin with alkyl or halogen groups in the para, ortho or di-ortho positions were investigated. While the incorporation reactions showed little dependence on porphyrin basicity, the Zn-P (P = porphyrin derivative) acid solvolysis reactions were faster the higher the basicity of the free base (H₂-P) compound. Equilibrium constants for the formation of cadmium porphyrins decreased with an increase in porphyrin basicity. The predeformed tetrakis(4-sulfonatophenyl)-β-octabromo-porphyrin reacted with Zn²⁺ about 10³ times faster than porphyrins of similar basicity. These results indicate how substituents on the phenyl and beta-pyrrole rings influence the solution chemistry of water soluble porphyrins.     

Tetralones as precursors for the synthesis of 2,2′-disubstituted 1,1′-binaphthyls and related compounds

Using tetralones as starting materials, the synthesis of biaryl compounds is described in this paper. The tetralones were initially converted into 1-bromo-3,4-dihydro-2-naphthalenecarbaldehydes before effecting aromatization into the corresponding naphthalenes. These products were then subjected to Suzuki-Miyaura cross-coupling reactions, with a variety of aromatic boronic acids containing substituents in the ortho position, to afford biaryl compounds. The biaryl compounds possess heteroatom containing substituents ortho to the newly formed biaryl axis.     

Stereochemistry of transmetalation of alkylboranes in nickel-catalyzed alkyl-alkyl cross-coupling reactions

Deuterium-labeled alkylborane reagents 2a and 2b were prepared and subjected to cross-coupling reactions in the presence of a nickel catalyst. NMR analysis of the products indicates that transmetalation from boron to nickel proceeds with retention of configuration. These results demonstrate that alkylnickel intermediates are configurationally stable under Suzuki cross-coupling conditions.     

Palladium-catalyzed meso-amination and amidation of porphyrins: marked acceleration with the Ni(II) central metal ion

The preparation of meso-amino and meso-amido substituted porphyrins was easily accomplished by palladium-mediated cross-coupling reactions of meso-brominated porphyrins with amines and amides. Ni(II) introduced as a central metal ion into the substrate porphyrin markedly accelerated the cross-coupling.     

Resonance raman spectra and excitation profiles of soret-excited metalloporphyrins

Resonance Raman spectra of nickel, chromium, and copper porphyrins, excited at their Soret maxima, show decreasing scattering intensity due to depolarized modes. This order correlates with diminished ¹Q(0-0) absorption in the porphyrins. The data are interpreted in terms of Jahn-Teller distortions in both Q and B states. General agreement between predicted and observed excitation profiles of nickel etioporphyrin I support a vibronic treatment of the excited states. The effect of tight focusing of the incident beam is to quench most Raman scattering intensity, except the 1384 cm^?1 line of the nickel complex.     

Functionalization of Pyridine and Quinoline Scaffolds by Using Organometallic Li-, Mg- and Zn-Reagents

This Review discusses the various methods for functionalizing pyridine and quinoline scaffolds, including direct selective metalation (DoM), halogen/metal exchange reactions, Li, Mg, and Zn insertion, and trans-metalation approaches, which are then followed by cross-coupling reactions of the Kumada or Negishi types. Selective deprotonation of aryl or pyridyl/quinolinyl derivatives can be performed using n-BuLi, LDA, and TMP-based different organolithium, -magnesium, and -zinc reagents. The functionalized pyridine and quinoline-based heterocyclic compounds were prepared by selectively deprotonating with presenting a directing functional group substituted pyridine/quinoline analogues in the presence of TMP-bases (TMP−Li, Mg, Zn reagents). Different aryl or alkyl Li, Mg, and Zn reagents with electron-donating and electron-withdrawing substituents undergo transition metal-catalyzed C(sp²)−C(sp²) and C(sp²)−C(sp³) types of cross-coupling reactions with pyridine/quinoline halides under mild conditions with the sustainable process producing complex N-heterocycles. Using moderate and sustainable reaction conditions, sensitive functional group tolerance, and inexpensive and low toxic chemicals, highly functionalization of pyridine and quinoline-based bioactive therapeutic scaffolds and natural products was accomplished. Therefore, in this article, we provide a succinct overview of the numerous synthetic strategies and practical methods used by various authors between 2010 and 2023 to functionalize pyridine and quinoline analogues using diverse Li, Mg, and Zn organometallic reagents.     

Synthesis of Octasubstituted Porphyrins

The synthesis of porphyrins having high solubility in organic solvents requires the presence of long chain aliphatic substituents. Such substituted porphyrins are readily prepared in good yields by extension of our general procedure¹ which involves the synthesis of α,β-unsaturated ketones, conversion of these to 3,4-disubstituted pyrroles followed by acid catalyzed condensations of these pyrroles with formaldehyde in the presence of air.     

Push–Pull Porphyrins via β-Pyrrole Functionalization: Evidence of Excited State Events Leading to High-Potential Charge-Separated States

A new set of free-base and zinc(II)-metallated, β-pyrrole-functionalized unsymmetrical push–pull porphyrins were designed and synthesized via β-mono- and dibrominated tetraphenylporphyrins using Sonogashira cross-coupling reactions. The ability of donors and acceptors on the push–pull porphyrins to produce high-potential charge separated states was investigated. The porphyrins were functionalized at the opposite β,β′-pyrrole positions of porphyrin ring bearing triphenylamine push groups and naphthalimide pull groups. Systematic studies involving optical absorption, steady-state and time-resolved emission revealed existence of intramolecular type interactions both in the ground and excited states. The push–pull nature of the molecular systems was supported by frontier orbitals generated on optimized structures, wherein delocalization of HOMO over the push group and LUMO over the pull group connecting the porphyrin π-system was witnessed. Electrochemical studies were performed to visualize the effect of push and pull groups on the overall redox potentials of the porphyrins. Spectroelectrochemical studies combined with frontier orbitals helped in characterizing the one-electron oxidized and reduced porphyrins. Finally, by performing transient absorption studies in polar benzonitrile, the ability of push–pull porphyrins to produce charge-separated states upon photoexcitation was confirmed and the measured rates were in the range of 10⁹ s⁻¹. The lifetime of the final charge separated state was around 5 ns. This study ascertains the importance of push–pull porphyrins in solar energy conversion and diverse optoelectronic applications, for which high-potential charge-separated states are warranted.     

Nickel-catalyzed migratory alkyl–alkyl cross-coupling reaction

The selective cross-coupling of activated electrophiles with unactivated ones has been regarded as a challenging task in cross-electrophile couplings. Herein we describe a migratory cross-coupling strategy, which can overcome this obstacle to access the desired cross-coupling products. Accordingly, a selective migratory cross-coupling of two alkyl electrophiles has been accomplished by nickel catalysis. Remarkably, this alkyl–alkyl cross-coupling reaction provides a platform to prepare 2°–2° carbon–carbon bonds from 1° and 2° carbon coupling partners. Preliminary mechanistic studies suggest that chain-walking occurs at both alkyl halides in this reaction, thus a catalytic cycle with the key step involving two alkylnickel(ii) species is proposed for this transformation.

The selective cross-coupling of activated electrophiles with unactivated ones has been regarded as a challenging task in cross-electrophile couplings.     

Conductive Fused Porphyrin Tapes on Sensitive Substrates by a Chemical Vapor Deposition Approach

Oxidative polymerization of nickel(II) 5,15‐diphenyl porphyrin and nickel(II) 5,15‐bis(di‐3,5‐tert‐butylphenyl) porphyrin by oxidative chemical vapor deposition (oCVD) yields multiply fused porphyrin oligomers in thin film form. The oCVD technique enables one‐step formation, deposition, and p‐doping of conjugated poly(porphyrins) coatings without solvents or post‐treatments. The decisive reactions and side reactions during the oCVD process are shown by high‐resolution mass spectrometry. Owing to the highly conjugated structure of the fused tapes, the thin films exhibit an electrical conductivity of 3.6×10^?2 S cm^?1 and strong absorption in the visible to near‐infrared spectral region. The formation of smooth conjugated poly(porphyrins) coatings, even on sensitive substrates, is demonstrated by deposition and patterning on glass, silicon, and paper. Formation of conductive poly(porphyrins) thin films could enable the design of new optoelectronic devices using the oCVD approach.