Halogenated meso-phenyl Mn(III) porphyrins as highly efficient catalysts for the synthesis of polycarbonates and cyclic carbonates using carbon dioxide and epoxides

New Co and Mn Catalysts Bearing ONO Ligands Containing Nucleophile for the Coupling of CO2 and Propylene Oxide

A series of novel ONO ligands bearing an ionic pendant-armed (hereinafter indicated as ONONu, where Nu corresponds to an anionic nucleophile) were synthesized, characterized, and successfully coordinated to cobalt and manganese precursors. New air-stable cobalt (III) complexes (1–6) and manganese (II) complexes (7 and 8) were obtained and characterized. Single crystal X-ray diffraction analysis of the Co(III) compound 5 confirmed the presence of two quaternized ligands coordinated to the metal and iodide as counterion. These novel complexes were revealed to be active catalysts in the coupling reaction of carbon dioxide and propylene oxide (PO) in different degrees of success. Among these, the manganese complex 8 afforded the best results towards the formation of propylene carbonate (PC) with a productivity of 256 kg PC/(kg cat·h), achieving a TON of 4860.

Recent Advances in Greener and Energy Efficient Alkene Epoxidation Processes

The chemical industry is considered to be one of the largest consumers of energy in the manufacturing sector. As the cost of energy is rising rapidly, coupled with the increasingly stringent standards for the release of harmful chemicals and gases into the environment, more attention is now focused on developing energy efficient chemical processes that could significantly reduce both operational costs and greenhouse gas emissions. Alkene epoxidation is an important chemical process as the resultant epoxides are highly reactive compounds that are used as platform chemicals for the production of commercially important products for flavours, fragrances, paints and pharmaceuticals. A number of epoxidation methods have been developed over the past decade with the ultimate aim of minimising waste generation and energy consumption. In this review paper, some of the recent advances in epoxides synthesis using energy efficient processes are discussed. The epoxidation methods may provide sustainability in terms of environmental impact and energy consumption.

Heterodinuclear Mg(II)M(II) (M=Cr, Mn, Fe, Co, Ni, Cu and Zn) Complexes for the Ring Opening Copolymerization of Carbon Dioxide/Epoxide and Anhydride/Epoxide

The catalysed ring opening copolymerizations (ROCOP) of carbon dioxide/epoxide or anhydride/epoxide are controlled polymerizations that access useful polycarbonates and polyesters. Here, a systematic investigation of a series of heterodinuclear Mg(II)M(II) complexes reveals which metal combinations are most effective. The complexes combine different first row transition metals (M(II)) from Cr(II) to Zn(II), with Mg(II); all complexes are coordinated by the same macrocyclic ancillary ligand and by two acetate co-ligands. The complex syntheses and characterization data, as well as the polymerization data, for both carbon dioxide/cyclohexene oxide (CHO) and endo-norbornene anhydride (NA)/cyclohexene oxide, are reported. The fastest catalyst for both polymerizations is Mg(II)Co(II) which shows propagation rate constants (k_p ) of 34.7 mM^-1  s^-1 (CO₂ ) and 75.3 mM^-1  s^-1 (NA) (100 °C). The Mg(II)Fe(II) catalyst also shows excellent performances with equivalent rates for CO₂ /CHO ROCOP (k_p =34.7 mM^-1  s^-1 ) and may be preferable in terms of metallic abundance, low cost and low toxicity. Polymerization kinetics analyses reveal that the two lead catalysts show overall second order rate laws, with zeroth order dependencies in CO₂ or anhydride concentrations and first order dependencies in both catalyst and epoxide concentrations. Compared to the homodinuclear Mg(II)Mg(II) complex, nearly all the transition metal heterodinuclear complexes show synergic rate enhancements whilst maintaining high selectivity and polymerization control. These findings are relevant to the future design and optimization of copolymerization catalysts and should stimulate broader investigations of synergic heterodinuclear main group/transition metal catalysts.

Metal-Cocatalyst Interaction Governs the Catalytic Activity of MII-Porphyrazines for Chemical Fixation of CO2

Chemical fixation of CO₂ to produce cyclic carbonates can be a green and atomic efficient process. In this work, a series of porphyrazines (Pzs) containing electron-withdrawing groups and central M^II ions (where M = Mg, Zn, Cu, and Co) were synthesized and investigated as catalysts for the cycloaddition of CO₂ to epoxides. Then, the efficiency of the Pzs was tested by varying cocatalyst type and concentration, epoxide, temperature, and pressure. Mg^IIPz bearing trifluoromethyl groups (1) showed the best conversion, producing, selectively, 78% of propylene cyclic carbonate (PCC), indicating that a harder and stronger Lewis acid is more effective for epoxide activation. Moreover, cocatalyst variation showed a notable effect on the reaction yields. Spectrophotometric titrations, MALDI-TOF mass spectra, and theoretical calculations suggest poisoning of the catalyst when tetrabutylammonium chloride (TBAC) and large amounts of tetrabutylammonium bromide (TBAB) were used in the system. The same was not observed for tetrabutylammonium iodide (TBAI), indicating that the metal-cocatalyst interaction may govern the reaction rate. In addition, two rare examples of crystalline structures were obtained, proving the distorted square pyramidal geometry with water molecule as axial ligand. This is one of the first studies reporting Pzs as catalysts for the chemical fixation of CO₂, and we believe that the intricate balance between cocatalyst concentration and conversion efficiency shown here may aid future studies in the area.

Mn(iii)–porphyrin catalysts for the cycloaddition of CO2 with epoxides at atmospheric pressure: effects of Lewis acidity and ligand structure

Mn(iii)–porphyrin catalysts with electron-withdrawing substituents were designed to uncover electronic and structural aspects in the cycloaddition of CO₂ with epoxides.

Nitrobenzene method: A keystone in meso-substituted halogenated porphyrin synthesis and applications

This review article briefly describes the available synthetic approaches for meso-arylporphyrins giving particular emphasis for one-pot nitrobenzene and nitrobenzene/NaY methods regarding the synthesis of meso-halogenated arylporphyrins. The review also describes the relevant applications of these halogenated porphyrins and their metalloporphyrin counterparts, prepared via nitrobenzene method, as photosensitizers for therapy (PDT and PDI), diagnostic (molecular contrast agents) and also for catalytic oxidation and CO2 cycloaddition reactions to epoxides.

Ni and Pd N-confused porphyrin complexes as catalysts for the synthesis of cyclic carbonates from epoxides and CO2

We have demonstrated the design of a novel bifunctional catalyst that is based on an N-confused tetraphenylporphyrin (NCTPP) motif for the cycloaddition of an epoxide to carbon dioxide via cooperative activation of the epoxide through a Pd(ii) or Ni(ii) metal center and a peripheral benzoate moiety with percent conversions of up to 99% and TON = 7000.

A biocompatible redox MRI probe based on a Mn(ii)/Mn(iii) porphyrin

A water-soluble fluorinated Mn^III/II porphyrin responds reversibly to ascorbate redox state as a turn-on MRI probe.

Aggregation and metal-complexation behaviour of THPP porphyrin in ethanol/water solutions as function of pH

The effect of pH change on 5,10,15,20-Tetrakis(4-hydroxyphenyl)-21H,23H-porphine (THPP) with its aggregation as function of water-ethanol mixture was studied with UV-vis, fluorescence, Raman and computational analysis. In neutral pH, THPP was present as free-base and, increasing the water amount, aggregation occurred with the formation of H- and J-aggregates. The aggregation constant and the concentration of dimers were calculated, other information about the dimer aggregation were evaluated by computational study. In acidic pH, by the insertions of two hydrogens in the porphyrin rings, the porphyrin changed its geometry with a ring deformation confirmed by red-shifted spectrum and quenching in fluorescence; at this low pH, increasing the water amount, the acidic form (THPPH₂)²⁺ resulted more stable due to a polar environment with stronger interaction by hydrogen bonding. In basic pH, reached by NH₄OH, THPP porphyrin was able to react with alkali metals in order to form sitting-atop complex (M₂THPP) confirmed by the typical absorption spectrum of metallo-porphyrin, Raman spectroscopy and by computational analysis.

A Cost-Efficient Method for Unsymmetrical Meso-Aryl Porphyrin Synthesis Using NaY Zeolite as an Inorganic Acid Catalyst

Herein we report the synthesis of unsymmetrical meso-aryl substituted porphyrins, using NaY zeolite as an inorganic acid catalyst. A comparative study between this method and the several synthetic strategies available in the literature was carried out. Our method presented a better, more cost-efficient rationale and displayed a significantly lower environmental impact. Furthermore, it was possible to verify the scalability of the process as well as the reutilization of the inorganic catalyst NaY (up to 6 times) without significant yield decrease. In addition, this method was applied to the synthesis of several other unsymmetrical porphyrins, from a low melting point porphyrin to mono-carboxylated halogenated unsymmetrical porphyrins, in yields higher than those found in the literature. Additionally, for the first time, two acetamide functionalized halogenated porphyrins were prepared in high yields. This methodology opens the way to the preparation of high yielding functionalized porphyrins, which can be easily immobilized for a variety of applications, either in catalysis or in biomedicine.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.