meso-Carbazole substituted palladium porphyrins: Efficient catalysts for visible light induced oxidation of aldehydes

The A3B and A2B2 type porphyrins having [Formula: see text]-butylcarbazole and [Formula: see text]-cyanophenyl groups are synthesized and characterized. Their palladium complexes have also been prepared and utilized as catalysts for the photo-oxidation reactions of aromatic aldehydes in good yields. Pd(II)porphyrins displayed decent phosphorescence at [Formula: see text]670 nm and were able to generate singlet oxygen upon light irradiation. The calculated singlet oxygen quantum yields for Pd(II)porphyrins were between 57% and 73%. The photo-catalytic application of Pd(II)porphyrins for aerobic oxidation of aromatic aldehydes is demonstrated.

Visible Light-Induced Aerobic Epoxidation of α,β-Unsaturated Ketones Mediated by Amidines

An aerobic photoepoxidation of α,β-unsaturated ketones driven by visible light in the presence of tetramethylguanidine (3b), tetraphenylporphine (H₂TPP), and molecular oxygen under mild conditions was revealed. The corresponding α,β-epoxy ketones were obtained in yields of up to 94% in 96 h. The reaction time was shortened to 4.6 h by flow synthesis. The mechanism related to singlet oxygen was supported by experiments and density functional theory (DFT) calculations.

Heterogenization of Ketone Catalyst for Epoxidation by Low Pressure Plasma Fluorination of Silica Gel Supports

Low pressure plasma was used for preparing heterogeneous organocatalysts 2-(A)-(C) suitable for dioxirane-mediated epoxidations. Heterogenization was accomplished by adsorption of the methyl perfluoroheptyl ketone (2) on fluorinated supports (A)-(C) deriving from the treatment of commercial C₈-silica gel in low pressure plasma fed with fluorocarbons. Catalyst 2-(C) proved to be the most efficient one, promoting epoxidation of an array of alkenes, including unsaturated fatty esters like methyl oleate (10) and the triglyceride soybean oil (11), with the cheap potassium peroxymonosulfate KHSO₅ (caroate) as a green oxidant. Notably, the perfluorinated matrix gives rise to the activation of caroate, generating singlet oxygen. Materials were characterized by infrared Attenuated Total Reflectance spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS ) and Emission Scanning Electron Microscope (FESEM).

Efficient photocatalytic oxygenation of alkenes by water soluble sensitizer in organic–water biphasic media

A new green, environmentally and economically photooxygenation of olefins by molecular oxygen in the presence of 4-carboxyl tetra phenyl porphyrin (H2TCPP), Rose Bengal (RB), Methylene Blue (MB) and some metallosensitizers (MS) such as cobalt phthalocyaninesulfonate (Coph(SO3H)[Formula: see text], MnTCPPCl, FeTCPPCl and SbTPP(OH)2 as water–soluble sensitizers in organic–water biphasic media at room temperature under visible light was illustrated. The products were obtained with 100% conversion by H2TCPP and 100% selectivity by Coph(SO3H)4. Also in this study, singlet oxygen production as the major route for oxidation of olefins was proved.

Modes of tetra(4-pyridyl)porphyrinatomanganese(III) ion intercalation inside natural clays

BACKGROUND

Metalloporphyrin ions, with planar shape, have been known to intercalate horizontally and diagonally between montmorillonite layers. Perpendicular intercalation inside montmorillonite has not been reported earlier. This work aims at achieving perpendicular intercalation inside montmorillonite in natural clays. Possible intercalation inside other forms of natural clay will also be investigated.

METHODS

Natural clays were purified and characterized. The naked clay powder was then refluxed with tetra(4-pyridyl)porphyrinatomanganese(III) ion (MnTPyP(+)) solution in methanol with continuous stirring for different times. Electronic absorption spectra, atomic absorption spectra, Fourier Transform infrared spectra, scanning electron microscopy and X-ray diffraction were all used in clay characterization and in intercalation study.

RESULTS

The natural clay involved different phases, namely montmorillonite, biotite, kaolinite, illite and traces of quartz. Montmorillonite clay allowed horizontal, diagonal and perpendicular intercalation of the metalloporphyrin ions. Biotite allowed only horizontal intercalation. The mode of intercalation was deduced by monitoring the clay inter-planar distance value change. Intercalation occurred inside both micro- and nano-size clay powders to different extents. The nano-powder (average size ~50 nm) showed uptake values up to 3.8 mg MnTPyP/g solid, whereas the micro-size powder (average size ~316 nm) exhibited lower uptake (2.4 mg MnTPyP/g solid). Non-expandable clay phases did not allow any intercalation. The intercalated MnTPyP(+) ions showed promising future supported catalyst applications.

CONCLUSIONS

Depending on their phase, natural clays hosted metalloporphyrin ions. Montmorillonite can allow all three possible intercalation geometries, horizontal, diagonal and for the first time perpendicular. Biotite allows horizontal intercalation only. Non-expandable clays allow no intercalation. Graphical abstractMetalloporphyrin complexes can be intercalated into montmorillonite in horizontal, perpendicular and diagonal geometries.

Highly active and selective catalysts for olefin hydrosilylation reactions using metalloporphyrins intercalated in natural clays

Mechanisms showing how the metalloporphyrin ions selectively catalyze olefin hydrosilylation reactions and the solvent-like behavior associated with the clay supported metalloporphyrin catalyst.

Effect of hydrogen bonding on catalytic activity of some manganese porphyrins in epoxidation reactions

Mn (III)-tetra phenyl porphyrin-acetate (MnTPPOAc) and some kinds of meso-phenyl substituted porphyrins by hydroxyl groups and their Mn (III) complexes were synthesized. These Mn -porphyrins were used as catalyst in the epoxidation of various alkenes with tetra-n-butylammonium hydrogen monopersulfate (n- Bu4NHSO5 ) as oxidant and tetra-n-butylammonium acetate (n- Bu4NOAc ) as the axial ligand. The following order of catalytic activity was observed for cyclooctene: T(2,3-OHP)PMnOAc ≫ T(2,4,6-OHP)PMnOAc ≥ T(4-OHP)PMnOAc ≥ T(2,6-OHP)PMnOAc ≥ TPPMnOAc and T(2,3-OHP)PMnOAc ≫ TPPMnOAc > T(4-OHP)PMnOAc > T(2,4,6-OHP)PMnOAc > T(2,6-OHP)PMnOAc for other alkenes. Different activity and stability of the catalysts were interpreted based on the hydrogen bonding between hydroxyl groups with appropriate orientation on the meso-position of the phenyl groups and axial bases or oxidant. T(2,3-OHP)PMnOAc catalyst has shown optimal condition for effective hydrogen bonding. In the case of other catalysts, electronic and steric factors overcome the hydrogen bonding effect.