Review of Conjugated Porphyrin Systems

Porphyrin macromolecules play critical roles in many natural processes. Studies are going on to mimic their role in natural systems and use them in various applications in artificial systems. When a porphyrin moiety is conjugated with carbon nanoallotropes, viz., carbon nanomaterials, carbon nanotubes, carbon nanospheres, etc., the hybrid molecules show optimized properties compared to the pristine molecules. In this review, various mechanisms of conjugating carbon nanoallotropes/carbon nanomaterials and porphyrins through stable chemical bond formation are discussed. The non-covalent interactions which cause their aggregation without disrupting their electronic structures are also discussed. This review also gives vital information on the utilization of conjugated systems effectively for society oriented applications.________________________________________

Role of redox-active axial ligands of metal porphyrins adsorbed at solid–liquid interfaces in a liquid-STM setup

In a liquid-STM setup environment, the redox behavior of manganese porphyrins was studied at various solid–liquid interfaces. In the presence of a solution of Mn(III)Cl porphyrins in 1-phenyloctane, which was placed at a conductive surface, large and constant additional currents relative to a set tunneling current were observed, which varied with the magnitude of the applied bias voltage. These currents occurred regardless of the type of surface (HOPG or Au(111)) or tip material (PtIr, Au or W). The additional currents were ascribed to the occurrence of redox reactions in which chloride is oxidized to chlorine and the Mn(III) center of the porphyrin moiety is reduced to Mn(II). The resulting Mn(II) porphyrin products were identified by UV–vis analysis of the liquid phase. For solutions of Mn(III) porphyrins with non-redox active acetate instead of chloride axial ligands, the currents remained absent.

Ru(II)Porphyrinate-Based Molecular Nanoreactor with Unusual Coordinative Properties and Extraordinary Chemical Selectivity in N–H Bond Carbene Insertion Reactions

A 5,15-bis(1,1’-biphenyl)porphyrin-based molecular clip covalently-linked to a stiff phenanthrene appended moiety yields a porphyrin-based macrocycle with a well-defined and relatively small cavity in the solid-state and in solution. Introduction of a Ru(II) ion into the porphyrin moiety followed by axial coordination of the inert and bulky diphenylcarbene ligand exo-to the macrocycle’s cavity affords a Ru(II)porphyrinate-based macrocycle able to promote the active-metal template [2]rotaxane synthesis in quantitative yield through the challenging single N–H bond carbenoid insertion. A detailed structural investigation of the Ru(II)porphyrinate-based macrocycle and the resulting asymmetrical [2]rotaxanes reveals that the synergy between the steric shielding provided by the hollow macrocyclic structure and the kinetic stabilization of otherwise labile coordinative bonds, warranted by the mechanical bond, can be used as principles for the design of molecular nanoreactors.

Ru(II)Porphyrinate-Based Molecular Nanoreactor with Unusual Coordinative Properties and Extraordinary Chemical Selectivity in N–H Bond Carbene Insertion Reactions

A 5,15-bis(1,1’-biphenyl)porphyrin-based molecular clip covalently-linked to a stiff phenanthrene appended moiety yields a porphyrin-based macrocycle with a well-defined and relatively small cavity in the solid-state and in solution. Introduction of a Ru(II) ion into the porphyrin moiety followed by axial coordination of the inert and bulky diphenylcarbene ligand exo-to the macrocycle’s cavity affords a Ru(II)porphyrinate-based macrocycle able to promote the active-metal template [2]rotaxane synthesis in quantitative yield through the challenging single N–H bond carbenoid insertion. A detailed structural investigation of the Ru(II)porphyrinate-based macrocycle and the resulting asymmetrical [2]rotaxanes reveals that the synergy between the steric shielding provided by the hollow macrocyclic structure and the kinetic stabilization of otherwise labile coordinative bonds, warranted by the mechanical bond, can be used as principles for the design of molecular nanoreactors.

Crystal structure of (15,20-bis(2,3,4,5,6-pentafluorophenyl)-5,10-{(4-methylpyridine-3,5-diyl)bis[(sulfanediylmethylene)[1,1′-biphenyl]-4′,2-diyl]}porphyrinato)nickel(II) dichloromethane x-solvate (x > 1/2)

The title compound, [Ni(C64H33F10N5S2)]·xCH2Cl2, consists of discrete NiII porphyrin complexes, in which the five-coordinate NiII cations are in a distorted square-pyramidal coordination geometry. The four porphyrin nitrogen atoms are located in the basal plane of the pyramid, whereas the pyridine N atom is in the apical position. The porphyrin plane is strongly distorted and the NiII cation is located above this plane by 0.241 (3) Å and shifted in the direction of the coordinating pyridine nitrogen atom. The pyridine ring is not perpendicular to the N4 plane of the porphyrin moiety, as observed for related compounds. In the crystal, the complexes are linked via weak C—H...F hydrogen bonds into zigzag chains propagating in the [001] direction. Within this arrangement cavities are formed, in which highly disordered dichloromethane solvate molecules are located. No reasonable structural model could be found to describe this disorder and therefore the contribution of the solvent to the electron density was removed using the SQUEEZE option in PLATON [Spek (2015). Acta Cryst. C71, 9–18].

Crystal structure of bis(4-methoxypyridine-κN)(meso-5,10,15,20-tetraphenylporphyrinato-κ4 N,N′,N′′,N′′′)iron(III) perchlorate

In the crystal structure of the title compound, [Fe(C44H28N4)(C6H7NO)2]ClO4, the FeIII ions are coordinated in an octahedral fashion by four N atoms of the porphyrin moiety and two N atoms of two 4-methoxypyridine ligands into discrete complexes that are located on inversion centers. Charge-balance is achieved by perchlorate anions that are disordered around twofold rotation axes. In the crystal structure, the discrete cationic complexes and the perchlorate anions are arranged into layers with weak C—H...O interactions between the cations and the anions. The porphyrin moieties of neighboring layers show a herringbone-like arrangement.

Helix-Sense-Selective Polymerization of Phenylacetylenes Having a Porphyrin and a Zinc-Porphyrin Group: One-Handed Helical Arrangement of Porphyrin Pendants

: Newly synthesized two kinds of achiral phenylacetylenes having a free-base- or a zinc-porphyrin (1 and Zn1, respectively) were polymerized by using a chiral rhodium catalyst system, Rh+(nbd)[(η6-C6H5)B–(C6H5)3] catalyst and (R)-(+)- or (S)-(–)-1-phenylethylamine ((R)- or (S)-PEA, respectively) cocatalyst. Poly(1) and poly(Zn1) in THF showed a Cotton signal at the absorption region of the porphyrin and the main chain in the circular dichroism (CD) spectra. This result suggests that poly(1) and poly(Zn1) exist in a conformation with an excess of one-handed helix sense and the porphyrin moiety arranged in chiral helical fashion. The one-handed helical structure of poly(1) could be sustained in a mixture of THF/HMPA (10/2, v/v) due to stabilizing by stacking effect of porphyrin moieties along the main chain. This is the first example about helix-sense-selective polymerization by using Rh+(nbd)[(η6-C6H5)B–(C6H5)3] catalyst. Additionally, poly(Zn1) showed about 10 times larger CD intensity in comparison with poly(1). This result suggests the regularity of arrangement of the porphyrin in poly(Zn1) is higher compared with poly(1). Spatial arrangement of porphyrins was achieved by utilizing a one-handed helical poly(phenylacetylenes) as a template.

Crystal structure of (diethyl ether-κO)[5,10,15,20-tetrakis(2-isothiocyanatophenyl)porphyrinato-κ4 N]zinc diethyl ether solvate

The crystal structure of the title compound, [Zn(C48H24N8S4)(C4H10O)]·C4H10O, consists of discrete porphyrin complexes that are located on a twofold rotation axis. The ZnII cation is fivefold coordinated by four N atoms of the porphyrin moiety and one O atom of a diethyl ether molecule in a slightly distorted square-pyramidal environment with the diethyl ether molecule in the apical position. The porphyrin backbone is nearly planar with the metal cation slightly shifted out of the plane towards the coordinating diethyl ether molecule. All four isothiocyanato groups of the phenyl substituents at the meso-positions face the same side of the porphyrin, as is characteristic for picket fence porphyrins. In the crystal structure, the discrete porphyrin complexes are arranged in such a way that cavities are formed in which additional diethyl ether solvate molecules are located around a twofold rotation axis. The O atom of the solvent molecule is not positioned exactly on the twofold rotation axis, thus making the whole molecule equally disordered over two symmetry-related positions.

Synthesis and characterization of β,β′-linked porphyrin-chlorin heterodimers and their metallic complexes

Two β,β′-linked porphyrin-chlorin heterodimers have been successfully synthesized with 4-fluorophenyl or 4-chlorophenyl substituted aldehyde as starting reagents. But those aldehydes with bulkier substituents did not lead to the corresponding heterodimers. These porphyrin-chlorin heterodimers and their metallic complexes have been characterized by X-ray crystallography. In all the structures, the pyrroline group in chlorin moiety and the pyrrole group in porphyrin moiety are directly connected by a single bond. Pyrroline ring has two sp[Formula: see text] hybridized carbons. The direct bonding makes the porphyrin and chlorin moieties closely contact with each other, pyrroline group and the pyrrole group forms a dihedral angle of ~70°. If porphyrin-chlorin heterodimers have bulkier substituents, the close contact could cause too much repulsion. That is probably why they can not be synthesized. For nickel complexes, the chlorin planes show large saddling and moderate ruffling conformation. The C–H⋯[Formula: see text] interaction could contribute to the saddling conformation. The distorted core makes dihedral angles and metal to metal distances between porphyrin and chlorin plane much smaller than those in their copper complexes. Their NMR, UV-visible and fluorescence spectral data have also been briefly discussed.