Confused Pyrrole Rings Research Articles

Chiral Interlocked Corrole Dimers Directly Linked at Inner Carbon Atoms of Confused Pyrrole Rings

A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C-C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials.

A study on the aromaticity and magnetic properties of N-confused porphyrins

In this paper, topological resonance energy (TRE) methods were used to describe the global aromaticity of nitrogen confused porphyrin (NCP) isomers. The TRE results show that all NCP isomers exhibit lower aromaticity than the normal porphyrins, and their aromaticity decreases as the number of confused pyrrole rings in the molecule increases. In the NCPs, global aromaticity decreases as the distance between the nitrogen atoms increases. The bond resonance energy (BRE) and circuit resonance energy (CRE) indices were applied to study local aromaticity and conjugated pathways. Both the BRE and CRE indices revealed that individual pyrrolic subunits maintain their strong aromatic character and are the main source of global aromaticity. Ring currents (RC) were analysed using the Hückel–London model. RC results revealed that the macrocyclic electron conjugation pathway is the main source of diatropicity. As the number of confused pyrrole rings in the molecule increases, its diatropicity gradually decreases. In the confused pyrrole rings of the NCP isomers, the diatropic RC passing through the β-positions is always weaker than that passing through the inner sections. This is unrelated to the location of the protonated or non-protonated nitrogen atom at the periphery of the molecule and must be ascribed to the unique properties of the confused pyrrole rings.

N-Confused Phlorin-Prodigiosin Chimera: meso-Aryl Oxidation and π-Extension Triggered by Peripheral Coordination.

An N-confused phlorin isomer bearing a dipyrrin moiety at the α-position of the confused pyrrole ring (1) was synthesized. PdII and BIII coordination at the peripheral prodigiosin-like moiety of 1 afforded the corresponding complexes 2 and 3. Reflux of 2 in triethylamine (TEA) converted the meso-phenyl into the PdII -coordinating phenoxy group to afford 4. Under the same reaction conditions, TEA was linked to the α-position of the dipyrrin unit in 3 as an N,N-diethylaminovinyl group to afford 5. Furthermore, peripheral coordination of BIII in 3 and 5 improved the planarity of the phlorin macrocycle and thus facilitated the coordination of AgIII at the inner cavity to afford 3-Ag and 5-Ag, respectively. These results provide an effective approach for developing unique porphyrinoids through peripheral coordination.

N‐Confused Phlorin‐Prodigiosin Chimera: meso‐Aryl Oxidation and π‐Extension Triggered by Peripheral Coordination

AbstractAn N‐confused phlorin isomer bearing a dipyrrin moiety at the α‐position of the confused pyrrole ring (1) was synthesized. PdII and BIII coordination at the peripheral prodigiosin‐like moiety of 1 afforded the corresponding complexes 2 and 3. Reflux of 2 in triethylamine (TEA) converted the meso‐phenyl into the PdII‐coordinating phenoxy group to afford 4. Under the same reaction conditions, TEA was linked to the α‐position of the dipyrrin unit in 3 as an N,N‐diethylaminovinyl group to afford 5. Furthermore, peripheral coordination of BIII in 3 and 5 improved the planarity of the phlorin macrocycle and thus facilitated the coordination of AgIII at the inner cavity to afford 3‐Ag and 5‐Ag, respectively. These results provide an effective approach for developing unique porphyrinoids through peripheral coordination.

Theoretical Study on Rotation of Pyrrole Rings in Porphyrin and N-Confused Porphyrin

Rotation of pyrrole rings in regular porphyrins and N-confused porphyrins is theoretically investigated by DFT calculations. While the inversion of the pyrrole rings in the regular porphyrins requires high activation energies (36.5-49.1 kcal/mol), the inversion of the confused pyrrole rings in the N-confused porphyrins requires much lower activation energies (18.1-24.5 kcal/mol). This marked difference can be explained by the intramolecular hydrogen bondings and aromatic stabilization due to the [18]annulenic substructures, where confusion and NH tautomerism play an important role. In both of the macrocycles, 360 degrees rotation of their pyrrole rings would be difficult possibly due to the small cavity. Alternatively, a reaction pathway for the production of N-fused porphyrin from N-confused porphyrin is obtained, which is consistent with the experimental observation.

Theoretical study on the structures and aromaticity of N-confused porphyrazine isomers

The energy and nucleus-independent chemical shift (NICS) of 95 isomers of N-confused porphyrazine (NCPz), including normal porphyrazine (N0CPz), N-confused porphyrazine (N1CPz), doubly N-confused porphyrazine (N2CPz), triply N-confused porphyrazine (N3CPz), and fully N-confused porphyrazine (N4CPz), have been calculated by the density-functional theory (DFT) method. The stability of NCPz decreased by increasing the number of confused pyrrole rings and the macrocycle tend to be destabilized stepwise by approximately +21 kcal/mol. The relative energies of the most stable isomers in confusion level are 0 kcal/mol (N0CPz-1), +23.481 (N1CPz-5), +41.849 (N2CPz-a4), +61.738 (N3CPz-b3), and +84.596 (N4CPz-b13), respectively. The most stable isomers of N2CPz, N3CPz, and N4CPz are not necessarily the most aromatic but rather nonaromatic, especially in the case of N3CPz and N4CPz. On the other hand, the magnitude of the aromaticity estimated by NICS for these isomers does not differ largely. The NICS values of the most aromatic isomers are −15.5411 (N0CPz-1), −14.0458 (N1CPz-2), −12.8171 (N2CPz-d1), −11.5961 (N3CPz-b6), and −12.8012 ppm (N4CPz-a6), respectively. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Programmed asymmetrical trimer formation of β-alkyl N-confused porphyrin zinc(II) complex

Self-coordination of β-alkyl N-confused porphyrin (NCP) zinc(II) complexes has been studied to reveal that asymmetrical trimers formed exclusively. A key factor to control the configuration of the trimers (symmetric or asymmetric) has been studied theoretically, and revealed that the steric environment around the peripheral nitrogen atoms as well as rotational angles of the confused pyrrole rings play a crucial role in trimer formation of β-alkyl NCP zinc(II) complexes.

N‐Confused and N‐Fused meso‐Aryl Sapphyrins

A state of (con)fusion: The introduction of a confused pyrrole ring into a meso-aryl sapphyrin framework destabilizes the macrocycle and forces a fusion reaction to occur. Subsequent metalation with rhenium results in further mutation to form a domino-fused sapphyrin with a fused penta-ring system (see scheme).

Acid–base properties and DNA-binding of water soluble N-confused porphyrins with cationic side-arms

Water soluble N-confused porphyrins, 5,10,15,20-tetrakis(alpha-pyridinio-p-tolyl)-2-aza-21-carbaporphyrin (pPyNCP) and its N-methyl derivative, 2-N-methyl-5,10,15,20-tetrakis(alpha-pyridinio-p-tolyl)-2-aza-21-carbaporphyrin (NMe-pPyNCP), have been synthesized by introducing cationic side-arms at the meso-positions of N-confused porphyrin. Their acid-base properties (pK(1-4)) and DNA-binding ability in aqueous solutions were elucidated in comparison with the corresponding porphyrin derivative. Photophysical behaviors of pPyNCP were largely influenced by buffer compositions and DNA structures, whereas NMe-pPyNCP is considerably robust against these factors. In addition, significant enhancement of the fluorescence was observed with NMe-pPyNCP by the addition of DNA. The unique properties of pPyNCP and NMe-pPyNCP stem from the confused pyrrole rings in the macrocycle.

Endocyclic extension of porphyrin π-system in etheno-bridged N-confused tetraphenylporphyrin

Etheno-bridged N-confused tetraphenylporphyrin was synthesized through flipping of the confused pyrrole ring and endocyclic extension of [18]annulenic pi-conjugated system was exemplified by the absorption spectra as well as the calculated Kohn-Sham orbitals.

Experimental and Theoretical Studies on Oligomer Formation of N‐Confused Porphyrin–Zinc(II) Complexes

Dimer formation of the N-confused porphyrin zinc(II), cadmium(II), and mercury(II) complexes was investigated experimentally as well as theoretically. The stable dimers were formed through coordination of the peripheral nitrogen atoms owing to flexible rotation of the confused pyrrole rings. The Z dimers were significantly more stable than the E dimers likely due to pi-pi interaction between the two confused pyrrole rings. The possible formation of higher oligomers such as trimers was suggested in the case of meso-unsubstituted derivatives.

Continuous-Wave and Pulse EPR Study of the Copper(II) Complex of N-Confused Tetraphenylporphyrin: Direct Observation of a σ Metal−Carbon Bond

N-confused or inverted porphyrins, a family of porphyrin isomers that contain a confused pyrrole ring connected through its alpha and beta' positions in the macrocycle, exhibit unique physical and chemical properties, like, for instance, the ability to stabilize unusual oxidation states of metals due to the reactivity of the inverted pyrrole. In this Article, a combined multifrequency continuous-wave and pulse electron paramagnetic resonance (EPR) study of the copper(II) complex of N-confused tetraphenylporphyrin (TPP) is presented. By use of pulse EPR methods like ENDOR and HYSCORE, the magnetic interactions between the unpaired electron of the compound and the surrounding nitrogen nuclei were revealed. Through 13C labeling of the macrocycle, a detailed study of the carbon hyperfine interaction became possible and provided further insight into the character of the metal-carbon bond. The observed hyperfine couplings of the ligand atoms in the first coordination sphere showed the presence of a remarkably strong sigma Cu-C bond and allowed for a detailed analysis of the spin delocalization over the porphyrin macrocycle. Interestingly, it was found that the observed delocalization is approximately 11% larger than the corresponding one for CuTPP.

Bis[iridium(I)] Complex of Inverted N-Confused Porphyrin

The reaction of N-confused tetraphenylporphyrin with IrCl(CO)2(p-toluidine) gave a novel bis[iridium(I)] complex, wherein the confused pyrrole ring took an inverted conformation.

Anion Binding Properties of N-Confused Porphyrins at the Peripheral Nitrogen

Ni(II), Pd(II), and Cu(II) complexes of N-confused porphyrin (NCP) exhibit anion binding properties through a hydrogen bonding interaction at the peripheral NH of confused pyrrole ring. The binding constants of the tetrakis(pentafluorophenyl)-NCP metal complexes (1-M, M= Ni, Pd, Cu) for various halide anions in CH2C12 increase in the order of F− > Cl− > Br− > I−, respectively. Zwitterionic resonance form of the NCP complexes as well as interactions between halide anions and a pentafluorophenyl group are suggested to be important for efficient anion binding.

Structures and ligand exchange of N-confused porphyrin dimer complexes with group 12 metals.

N-confused 5,20-diphenylporphyrin (NCDPP, 1) formed 2:2 dimer complexes with group 12 metals both in the solid state and in solution. X-ray single-crystal analyses of the Zn(II) and Cd(II) complexes (7, 8) revealed that each metal ion is coordinated with three inner core nitrogens and a peripheral nitrogen of the other NCDPP in the pair. In the (1)H NMR spectra of 7, 8, and the Hg(II) complex (9), the outer alpha-H signals of the confused pyrrole ring appeared in the upfield region at 2.57, 3.44, and 3.60 ppm, respectively, due to the ring current effect by the coordinated porphyrins. In the case of the Cd(II) and Hg(II) complexes (8, 9), additional magnetic couplings with the metal nuclei of the partner rings were observed. The equilibrium constants (K) of the monomer exchange reaction at 25 degrees C were determined to be 2.5, 1.3, and 0.6 for the (Zn-Cd), (Cd-Hg), and (Zn-Hg) heterodimer complexes, respectively, from the (1)H NMR spectra of a solution containing two different dimers. Furthermore, a metal-transfer reaction from a Zn(II) NCP dimer complex to the free base porphyrin was demonstrated.

Theoretical Study of Stability, Structures, and Aromaticity of Multiply N-Confused Porphyrins

The total electronic energy and nucleus-independent chemical shift (NICS) of 95 isomers of N-confused porphyrin (NCP: normal porphyrin (N(0)CP), singly N-confused porphyrin (N(1)CP), doubly N-confused porphyrin (N(2)CP), triply N-confused porphyrin (N(3)CP), and fully N-confused porphyrin (N(4)CP)) have been calculated by the density functional theory (DFT) method. The stability of NCP decreased by increasing the number of confused pyrrole rings. Namely, the relative energies of the most stable isomers in each confusion level increased in a stepwise manner approximately by +18 kcal/mol: 0 (N(0)CP1), +17.147 (N(1)CP2), +37.461 (N(2)CPb3), +54.031 (N(3)CPd6), and +65.636 kcal/mol (N(4)CPc8). In this order, the mean plane deviation of these isomers increased from 0.000 to 0.123, 0.170, 0.215, and 0.251 A, respectively. The unusual tautomeric forms of pyrrole ring with an sp(3)-carbon were found in the stable forms of N(3)CP and N(4)CP. The NICS values at the mean position of the 24 core atoms were nearly the same for the most aromatic isomers regardless of the confusion level: -15.1280 (N(0)CP1), -13.8493 (N(1)CP2), -13.7267 (N(2)CPd1), -11.7723 (N(3)CPb5), and -13.6224 ppm (N(4)CPa6). The positive correlation between aromaticity and stability was inferred from the plots of NICS and the relative energy of NCP for N(0)CP, N(1)CP, and trans-N(2)CP. On the other hand, the correlation was negative for cis-N(2)CP, N(3)CP, and N(4)CP isomers.

Acid-base and spectroelectrochemical properties of doubly N-confused porphyrins.

The cis-doubly N-confused porphyrin, H2N2CP, containing two adjacent confused pyrrole rings has been investigated from the point of view of its acid-base and electrochemical behavior in dichloromethane. This novel porphyrin isomer can form two metal-carbon bonds in the central core, stabilizing metal ions in unusually high oxidation states. Furthermore, the two outside N-pyrrole atoms remain available for acid-base and specific solvent interactions. Protonation of the pyrrole N atoms proceeds according to two successive steps, while only a single deprotonation step has been observed in the presence of bases. Similarly, in the case of the silver and copper complexes the protonation and deprotonation of the outer pyrrole rings have been detected, confirming the structure of the metalated species as M(III)-HN2CP. The electrochemical reduction of the metal ions (III/II redox process) and oxidation of the macrocycle ring have been detected respectively at -0.9 and 1.4 V based on spectroelectrochemical measurements in conjunction with the acid/base equilibrium studies. Additional waves observed around -0.5 and 1.3 V have been assigned to redox processes involving water molecules associated with the doubly N-confused porphyrins.