N-methyl-21-thiaporphyrins

We synthesized five N-methyl-meso-tetraaryl-21-thiaporphyrins in 55–60 % yield by treating the appropriate meso-tetraaryl-21-thiaporphyrin with CH3I. The N-methyl-21-thiaporphyrins were characterized by HRMS, 1D and 2D NMR spectroscopy, absorption spectroscopy, fluorescence spectroscopy and electrochemical techniques and the structure of one of the compounds was obtained by X-ray crystallography. 1D and 2D NMR spectroscopy were used to identify all of the resonances observed in the 1H NMR spectra of the N-methyl-21-thiaporphyrins. NMR studies indicated that the methylation occurred at the pyrrole ring that is opposite to the thiophene ring. In the 1H NMR spectra, the methylation resulted in significant upfield shifts of the pyrrole and thiophene protons; the maximum shifts were noted for the protons of the N-methylated pyrrole ring of the N-methyl-21-thiaporphyrins. The X-ray structure of one of the N-methyl-21-thiaporphyrins revealed significant deviation of the N-methylated pyrrole ring from the reference plane defined by the four meso carbon atoms, and the porphyrin ring is strongly distorted compared to the 21-thiaporphyrin ring. The absorption studies revealed that the N-methyl-21-thiaporphyrins showed four Q bands and one strong Soret band, which were bathochromically shifted compared to those of the 21-thiaporphyrins. The electrochemical studies on the N-methyl-21-thiaporphyrins indicated that the oxidation potentials became less positive and there were negligible shifts in the reduction potentials; the HOMO–LUMO energy gap decreased compared with that of the 21-thiaporphyrins. The N-methyl-21-thiaporphyrins are weakly fluorescent with low quantum yields and singlet-state lifetimes. The spectral and electrochemical studies indicated that N-methylation of the pyrrole ring of 21-thiaporphyrins significantly alters the electronic properties of the 21-thiaporphyrin macrocycle

Formation of unusual dithiaphlorins from condensation of 2,5-bis(arylhydroxymethyl)thiophene and pyrrole

The first example of an unusual 21,23-dithiaphlorin containing pyrrole and aryl groups at the sp³ meso carbon that is present between the pyrrole and thiophene rings was isolated from the condensation of 2,5-bis(arylhydroxymethyl) and pyrrole under mild acid catalyzed conditions. The crystal structure revealed that the macrocycle is significantly distorted because of the presence of the sp³ meso carbon

Synthesis, structure and spectral and electrochemical properties of meso-tetraaryl-27-thiasapphyrins

An alternate synthetic route was developed for tetraaryl 27-thiasapphyrins by condensation of meso-aryl dipyrromethanes with 2,5-bis(p-tolylhydroxymethyl)thiophene under acid-catalyzed conditions. Previously, 27-thiasapphyrins have been prepared by a multistep synthesis using 2,2′-bipyrrole as the key precursor. In our strategy, the pyrrole–pyrrole bond was generated to form 27-thiasapphyrins by oxidative coupling of meso-aryl dipyrromethane and 2,5-bis(p-tolylhydroxymethyl)thiophene, and the desired 27-thiasapphyrins were isolated in 8–12 % yields. The crystal structure of one of the 27-thiasapphyrins indicates that the macrocycle is almost planar and the thiophene sulfur atom is in the plane whereas the four pyrrole nitrogen atoms slightly deviate from the plane defined by four meso carbon atoms. Absorption spectroscopy showed four well defined Q bands in 590–770 nm and one strong Soret band in 470–480 nm region for 27-thiasapphyrins. The 27-thiasapphyrins are stable under redox conditions and undergo two-to-three reversible oxidations and one-to-two reversible reductions. The macrocycles are weakly fluorescent with low quantum yields and singlet state lifetimes

Synthesis, structure and properties of a five-coordinate oxophosphorus(V) meso-triphenylcorrole

Treatment of six-coordinate (5,10,15-triphenylcorrole)dihydroxyphosphorus(V) [P(TPC)(OH) 2] with Trifluoroacetic Acid (TFA) in CH2Cl2 for 30 min at room temperature followed by recrystallization gave stable five-coordinate (5,10,15-triphenylcorrole)oxophosphorus(V) [P(TPC)O] in quantitative yield. The formation of [P(TPC)O] from [P(TPC)(OH) 2] in the presence of TFA was also monitored by NMR, absorption and fluorescence spectroscopic titration studies. The structure of the isolated [P(TPC)O] was confirmed by X-ray crystallography. In [P(TPC)O], the corrole ring is distorted, and the PV ion is displaced by 0.456 Å from the N4 plane towards the axial oxygen atom. This is unlike six-coordinate (5,10,15-triphenylcorrole)dimethoxyphosphorus(V) [P(TPC)(OCH3) 2], in which the PV ion lies in the porphyrin plane. NMR, absorption and fluorescence spectroscopy and electrochemical studies indicate that [P(TPC)O] exhibits interesting and distinct properties, which differ from the six-coordinate [P(TPC)(OCH3) 2]. Attempts to reduce the PV complex [P(TPC)O] to its corresponding PIII complex by treating it with LiAlH4 resulted in the formation of six-coordinate (5,10,15-triphenylcorrole)dihydridophosphorus(V) [P(TPC)H2]

Synthesis of Tellurabenziporphyrin and Its Pd(II) Complex

An unprecedented tellurabenziporphyrin containing C, N, and Te donor atoms was synthesized by condensing benzitripyrrane and tellurophene diol under acid catalyzed conditions. The tellurabenziporphyrin readily forms a Pd­(II) complex when treated with PdCl₂ in CHCl₃/CH₃CN. The crystal structures of tellurabenziporphyrin and its Pd­(II) complex revealed that the benzene ring hinders the π-electron delocalization. An unusual five-membered ring formed inside the macrocycle due to the strong interaction between “Te” and “N” in the Pd­(II) complex

Synthesis, structure and properties of core-modified pentaphyrins containing six meso carbons

Our successful synthesis of nonaromatic 24π core-modified pentaphyrins containing six meso carbons is reported. The pentaphyrins were prepared by [3+2] condensation of butane-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with different meso-aryl tripyrromethanes under mild acid-catalyzed conditions. By using this method, we obtained two stable, core-modified pentaphyrins containing six meso carbons in acceptable yields. The pentaphyrins were characterized by HR-MS, 1D, 2D NMR, absorption and electrochemical techniques and also by X-ray crystallography for one of the pentaphyrin macrocycles. The crystal structure revealed that the macrocycle is almost planar and one of the thiophene rings, which is positioned opposite to the ethene bridged meso-carbons, is inverted. Our studies revealed that the macrocycles in their protonated form have specific sensing ability for CH3COO− ions

Rhenium(I) Tricarbonyl Complexes of <i>meso</i>-Tetraaryl-21,23-diheteroporphyrins

The dithia/diselena <i>meso</i>-tetraarylporphyrins have a lesser tendency to form metal complexes because of the larger size of the heteroatom(s), which shrinks the cavity size, and the heteroatoms also have poor coordinating ability to bind metal ions. The first example of a rhenium­(I) tricarbonyl complex of 21,23-diselenaporphyrin was synthesized by treating 5,10,15,20-tetra-<i>p</i>-tolyl-21,23-diselenaporphyrin with Re­(CO)₅Cl in chlorobenzene at reflux temperature and its structural properties were compared with our earlier reported rhenium­(I) complex of tetraaryl-21,23-dithiaporphyrin. The crystal structures of rhenium­(I) complexes of diheteroporphyrins revealed that the Re^I ion binds to both the Se/S atoms and one of the N atoms of the porphyrin core along with three terminal carbonyl groups in an octahedral fashion. The rhenium­(I) complexes of 21,23-diheteroporphyrins are stabilized by a large counterion, the trichloro-bridged dirhenium­(I) ion. We also present a detailed account of the spectral and redox properties of rhenium­(I) tricarbonyl complexes of 21,23-diheteroporphyrins

Synthesis and Functionalization of BF₂‑Complexes of <i>meso</i>-Free 25-Oxasmaragdyrin

BF₂-complex of <i>meso</i>-free 25-oxasmaragdyrin is synthesized under simple reaction conditions in high yield, and the reactivity of <i>meso</i>-free carbon atom was demonstrated by carrying out functionalization followed by coupling reactions