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.     

Catalytic enantioselective addition of diethylzinc to 1,3-dithian-2-yl substituted aliphatic aldehydes: a new approach to optically active 2-(hydroxyalkyl)-1,3-dithianes

Asymmetric synthesis of 2-(hydroxyalkyl)-1,3-dithianes was achieved in good yields of up to 81% by using various 1,3-dithian-2-yl-substituted aliphatic aldehydes as substrates in the catalytic enantioselective addition of diethylzinc. With fair enantiomeric ratios of up to 85:15 in the enantiocontrolled ethylation step this synthetic approach provides an entry towards potential chiral building blocks.     

Dimeric assemblies from 1,2,3-triazole-appended Zn(II) porphyrins with control of NH-tautomerism in 1,2,3-triazole

Cu(I)-catalyzed 1,3-dipolar cycloaddition of meso-ethynyl Zn(II) porphyrin with benzyl azide efficiently provides meso-1-benzyl-1H-1,2,3-triazolyl Zn(II) porphyrin, which assembles to form a slipped cofacial dimer by the complementary coordination of the triazole nitrogen atom at the 3-position to the zinc center of a second porphyrin moiety both in the solid and solution states. Removal of the benzyl protection and introduction of a 2-ethoxycarbonylphenyl moiety greatly stabilize the dimeric assembly through an additional hydrogen bonding interaction between the NH proton of 2H-1,2,3-triazole and the carbonyl oxygen.     

Electronic control of product formation in the rearrangement of 1,3-dithian-2-yl-arylmethanols

1,3-Dithian-2-yl-phenylmethanols undergo efficient rearrangement to afford 2-phenyl-6,7-dihydro-5H-1,4-dithiepines. The reactions were found to show remarkable variation in products formation that is dictated by the substituents on the aryl ring.     

Photocatalytic CO2 Reductions Catalyzed by meso-(1,10-Phenanthrolin-2-yl)-Porphyrins Having a Rhenium(I) Tricarbonyl Complex

We have prepared Zn and free-base porphyrins appended with a fac-Re(phen)(CO)₃Br (where phen is 1,10-phenanthroline) at the meso position of the porphyrin, and performed photocatalytic CO₂ reduction using porphyrin–Re dyads in the presence of either triethylamine (TEA) or 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as an electron donor. The Zn porphyrin dyad showed a high turnover number for CO production compared with the free-base porphyrin dyad, suggesting that the central Zn ion of porphyrin plays an important role in suppressing electron accumulation on the porphyrin part and achieving high durability of the photocatalytic CO₂ reduction using both TEA and BIH. The effect of acids on the CO₂ reduction was investigated using the Zn porphyrin–Re dyad and BIH. Acetic acid, a relatively strong Brønsted acid, rapidly causes the porphyrin's color to fade upon irradiation and dramatically decreases CO production, whereas proper weak Brønsted acids such as 2,2,2-trifluoroethanol and phenol enhance the CO₂ reduction.     

Synthesis of meso-5-azaindolyl-appended Zn(II) porphyrins via Pd-catalyzed annulation

Pd-catalyzed annulation reaction of meso-hexynyl Zn(II) porphyrin with 4-amino-3-iodopyridine efficiently provides meso-3-(5-azaindolyl)-substituted Zn(II) porphyrin as a major product, which assembles to form a slipped cofacial dimer by the complementary coordination of the pyridine moiety to the Zn(II) center. 2-iodoaniline and 2-iodophenol also undergo this [3 + 2] annulation with the meso-hexynyl Zn(II) porphyrin to furnish meso-indolyl- and benzofuranyl-substituted Zn(II) porphyrins, respectively.     

Synthesis of 2-(1,3-Diselenan-2-yl)thiophene from 1,3-Propanediselenol and 2-Thiophenecarbaldehyde

Russian Journal of Organic Chemistry -     

Sequential deprotonation of meso-(p-hydroxyphenyl)porphyrins in DMF: from hyperporphyrins to sodium porphyrin complexes

Sequential deprotonations of meso-(p-hydroxyphenyl)porphyrins (p-OHTPPH2) in DMF + H2O (V/V = 1:1) mixture have been verified to result in the appearance of hyperporphyrin spectra. However, when the deprotonations of these p-OHTPPH2 are carried out in DMF, the spectral changes differ considerably from those in the mixture mentioned above. At low [OH-], the optical spectra in the visible region are still considered to have characteristics of hyperporphyrin spectra. Further deprotonation at much higher basicity makes the optical spectra form three-banded spectra similar to those in the acidic solution. To clarify the molecular origins of these changes, UV-vis, resonance Raman (RR), proton nuclear magnetic resonance (1H NMR) experiments are carried out. Our data give evidence that p-OHTPPH2 in DMF can be further deprotonated of pyrrolic-H by higher concentrated NaOH, due to an aprotic medium like DMF effectively weakening the basicity of the porphyrin relative to that of the NaOH, and coordinates with two sodium ions (except the sodium ions that interact with the peripherial phenoxide anions) to form the sodium complexes of p-OHTPPH2 (Na2P, to lay a strong emphasis on the sodium ions that coordinate with the central nitrogen atom), which can be regarded as the porphyrin anions being perturbed by the sodium cations due to their highly ionic character. The negative centers generated by deprotonation of pyrrolic-H and phenolic-H are not thoroughly delocalized between the substituents and the porphyrin ring. Thus the negative centers generated by deprotonation of pyrrolic-H only act as electron-donating groups on the porphyrin pi system, and the negative charges of the phenoxide anion are also mainly localized on the peripheral substituents. As a result, the porphyrin pi orbitals cross over the phenoxide anion pi orbital and turn into HOMOs, which turns hyperporphyrin spectra of deprotonated phenolic-H of p-OHTPPH2 into three-banded spectra of regular metalloporphyrins.     

Synthesis and Properties of (1,3-Dioxolan-2-yl)furans

Reaction of formylfurancarboxylates with excess ethylene glycol in the presence of p-toluene-sulfonic acid gives rise to (1'3-dioxolan-2-yl)furancarboxylates. Reduction of these products with lithiumaluminum hydride proceeds with preservation of the dioxolane ring. Except for 5-(1'3-dioxolan-2-yl)(hydr-oxymethyl)-2-methyl-3-furan, the obtained alcohols are unstable. Chlorides derived from them decomposeunder conditions of the Michaelis-Becker reaction, no phosphorylation products are formed. By contrast'the above-mentioned stable alcohol by treatment with thionyl chloride in the presence of pyridine is convertedto a fairly stable chloromethylfuran. The latter compound reacts with sodium diethyl phosphite in benzene to form the corresponding phosphonate that exists as a 1:4 mixture of two spectroscopically discernible conformers.     

Photophysical and electrochemical properties of meso-substituted thien-2-yl Zn(II) porphyrins

The influence of the thiophene ring on the ground and excited state properties of the porphyrin ring is investigated, when substituted at the meso-position. A series of mono-, di-, tri-, and tetra- meso-thien-2-yl porphyrins are studied and discussed with respect to the reference compounds zinc(II)-5,10,15,20-tetra(thien-2'-yl)porphyrin ( 1a) and zinc(II)-5,10,15,20-tetraphenylporphyrin (ZnTPP). The extended conjugated system zinc(II)-5-(5'-(5'-ethynyl-2'-thiophenecarboxaldehyde)thien-2'-yl)-10,15,20-triphenylporphyrin ( 4d) is also studied and shows enhanced charge transfer character due to the presence of the terminal aldehyde accepting group. A detailed analysis of ground and excited state UV-vis absorption, steady-state and time-resolved fluorescence, laser flash photolysis, and electrochemical data all point toward substantial electronic communication between the central Zn(II) porphyrin ring and the meso-thien-2-yl substituents, which is evident from excited state charge transfer character.     

Synthesis of New 2-(Oxiran-2-yl)-1,3-oxazoles

Russian Journal of General Chemistry - Reaction of 2-chloro-N-(2,2-dichloro-1-cyanovinyl)acetamide with dimethylamine gave 5-(dimethylamino)-2-[(dimethylamino)methyl]-1,3-oxazole-4-carbonitrile,...     

2-(1,3-Dithiolan-2-ylidene)-5-(1,3-dithian-2-ylidene)-1,3,4,6- tetrathiapentalene(DHDA-TTP), a hybrid of BDH-TTP and BDA-TTP,and its metallic cation-radical salts

The synthesis and electrochemical properties of the DHDA-TTP donor, a hybrid of 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) and 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP), has been investigated, and its ability to form metallic cation-radical salts is elucidated.