Vanadyl β-tetrabromoporphyrin: synthesis, crystal structure and its use as an efficient and selective catalyst for olefin epoxidation in aqueous medium

Enhanced Catalytic Activity of Binuclear Oxidovanadium(IV) Bisbenzimidazole Linked Porphyrin Dimer for the Generation of Biologically Active 3,4-Dihydropyrimidinones and Their Corresponding Thiones

Binuclear vanadyl(IV) porphyrin (V2BP), where two vanadium(IV) porphyrin macrocycles are linked through benzimidazole units at the β-positions, has been prepared and characterized with various techniques, such as UV-vis, Fourier transform-infrared, electron paramagnetic resonance, cyclic voltammetry, density functional transform calculations, and mass spectrometry. V2BP exhibits a red shift (Δλmax = 10 nm) in the Soret band as compared with unsubstituted parent vanadyl(IV) meso-tetraphenylporphyrin (VP). The synthesized binuclear vanadyl(IV) porphyrin (V2BP) has further been studied as a catalyst to explore a single-pot multicomponent Biginelli reaction producing biologically active 3,4-dihydropyrimidin-2-(1H)-one (DHPM)-based biomolecules and the corresponding thiones under solvent-free conditions and its catalytic activity has been compared with vanadyl(IV) meso-tetraphenylporphyrin (VP). Several reaction conditions, such as the amount of catalyst, time, solvent, and temperature, have been optimized to obtain the maximum yield of DHPMs or thiones. The synthesized β-functionalized V2BP porphyrin dimer manifests much higher conversion (84-95% yield) of DHPMs or the corresponding thiones under the optimized reaction conditions with high TON (4454-5037) and TOF (1113-1259 h-1) values for the one-pot multicomponent Biginelli reaction as compared to the literature. The catalyst exhibited excellent recyclability up to 10 cycles.

Oxido-Molybdenum(V) Corroles as Robust Catalysts for Oxidative Bromination and Selective Epoxidation Reactions in Aqueous Media under Mild Conditions

Two new meso-substituted oxido-molybdenum corroles were synthesized and characterized by various spectroscopic techniques. In the thermogram, MoO[TTC] (1) exhibited excellent thermal stability up to 491 °C while MoO[TNPC] (2) exhibited good stability up to 318 °C. The oxidation states of the molybdenum(V) were verified by electron paramagnetic resonance (EPR) spectroscopy and exhibited an axial compression with d_xy¹ configuration. Oxido-molybdenum(V) complexes were utilized for the selective epoxidation of various olefins with high TOF values (2066-3287 h^-1) in good yields in a CH₃CN/H₂O (3:2, v/v) mixture in the presence of hydrogen peroxide as a green oxidant and NaHCO₃ as a promoter. The oxidative bromination catalytic activity of oxido-molybdenum(V) complexes in an aqueous medium has been reported for the first time. Surprisingly, MoO[TNPC] (2) biomimics of the vanadium bromoperoxidase (VBPO) enzyme activity exhibited remarkably high TOF values (36 988-61 646 h^-1) for the selective oxidative bromination of p-cresol and other phenol derivatives. Catalyst MoO[TNPC] (2) exhibited higher TOF values and better catalytic activity than catalyst MoO[TTC] (1) due to the presence of electron-withdrawing nitro groups evident from cyclic voltammetric studies.

Facile Synthesis of β-Tetracyano Vanadyl Porphyrin from Its Tetrabromo Analogue and Its Excellent Catalytic Activity for Bromination and Epoxidation Reactions

Complex 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[V^IVOTPP(CN)₄], 2} has been prepared by nucleophilic substitution of β-bromo groups of the corresponding 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[V^IVOTPP(Br)₄], 1} using CuCN in quinoline. Both complexes show biomimetic catalytic activity similar to enzyme haloperoxidases and efficiently brominate various phenol derivatives in the presence of KBr, H₂O₂, and HClO₄ in the aqueous medium. Between these two complexes, 2 exhibits excellent catalytic activity with high turnover frequency (35.5-43.3 s^-1) due to the strong electron-withdrawing nature of the cyano groups attached at β-positions and its moderate nonplanar structure as compared to 1 (TOF = 22.1-27.4 s^-1). Notably, this is the highest turnover frequency value observed for any porphyrin system. The selective epoxidation of various terminal alkenes using complex 2 has also been carried out, and the results are good, specifying the importance of electron-withdrawing cyano groups. Catalysts 1 and 2 are recyclable, and the catalytic activity proceeds through the corresponding [V^VO(OH)TPP(Br)₄] and [V^VO(OH)TPP(CN)₄] intermediates, respectively.

V-Porphyrins Encapsulated or Supported on Siliceous Materials: Synthesis, Characterization, and Photoelectrochemical Properties

Metalloporphyrin-containing mesoporous materials, named VTPP@SBA, were prepared via a simple anchoring of vanadyl porphyrin (5,10,15,20-Tetraphenyl-21H,23H-porphine vanadium(IV) oxide) through a SBA-15-type mesoporous material. For comparison, vanadyl porphyrin was also impregnated on SiO2 (VTPP/SiO2). The characterization results of catalysts by XRD, FTIR, DR-UV-vis, and EPR confirm the incorporation of vanadyl porphyrin within the mesoporous SBA-15. These catalysts have also been studied using electrochemical and photoelectrochemical methods. Impedance measurements confirmed that supporting the porphyrin in silica improved the electrical conductivity of samples. In fact, when using mesoporous silica, current densities associated with oxidation/reduction processes appreciably increased, implying an enhancement in charge transfer processes and, therefore, in electrochemical performance. All samples presented n-type semiconductivity and provided an interesting photoelectrocatalytic response upon illumination, especially silica-supported porphyrins. This is the first time that V-porphyrin-derived materials have been tested for photoelectrochemical applications, showing good potential for this use.

Ordered assembly of non-planar vanadyl-tetraphenylporphyrins on ultra-thin iron oxide

Stabilizing ordered assemblies of molecules represents the first step towards the construction of molecular devices featuring hybrid (organic-inorganic) interfaces where molecules can be easily functionalized in view of specific applications. Molecular layers of planar metal-tetraphenylporphyrins (MTPP) grown on an ultrathin iron oxide [namely Fe(001)-p(1 × 1)O] show indeed a high degree of structural order. The generality of such a picture is tested by exploiting non-planar porphyrins, such as vanadyl-TPP (VOTPP). These molecules feature a VO²⁺ ion in their center, with the O atom protruding out of the plane of the porphyrin ring. In this work, by employing diffraction, photoemission and X-ray absorption, we prove that non-planar VOTPP can nevertheless form a square and ordered superstructure, where porphyrin molecules lie flat with respect to the underlying substrate. Ab initio density functional theory simulations are used to elucidate the VO bond orientation with respect to the iron substrate.

Selective epoxidation of olefins by vanadylporphyrin [VIVO(TPP)] and electron deficient nonplanar β-octabromovanadylporphyrin [VIVO(TPPBr8)]

Meso-tetraphenylporphyrinatooxidovanadium(IV) [VIVO(TPP)] (1) and 2,3,7,8,12,13, 17,18-octabromo-meso-tetraphenylporphyrinatooxidovanadium(IV) [VIVO(TPPBr[Formula: see text]] (2) were synthesized and characterized by various spectroscopic techniques. 1 and 2 were utilized as efficient catalysts for the selective epoxidation of olefins. Catalyst 2 shows very high catalytic activity (TOF = 8783–13108 h[Formula: see text] as compared to 1 (TOF = 2175–3296 h[Formula: see text]. The catalysts are recyclable, as their recyclability was checked for four cycles and show only minor reduction of their efficiency.

A Theoretical Study of Metalloporphyrin-Based Fluorescent Array Sensor using Density Functional Theory

The influences of metal atoms on optimized geometry structures, relative energies, frontline molecular orbitals, and binding energies of metalloporphyrin-based fluorescent array sensor were systematically investigated by density functional theory (DFT) at B3LYP/LAN2DZ level. DFT calculated results reveal that the selected metal atoms in the center of the metalloporphyrin plane provide difference performances of metalloporphyrin-based fluorescent array sensor for the rapid determination of trimethylamine. The calculated binding energies have displayed in the following order at the most stable states: zinc porphyrin (ZnP) < copper porphyrin (CuP) < silver porphyrin (AgP) < iron porphyrin (FeP) < tin porphyrin (SnP) < cobalt porphyrin (CoP) < ruthenium porphyrin (RuP) < manganese porphyrin (MnP). Therefore, this theoretical study provides a design mechanism for how to choose a proper metal atom for low or high concentration trimethylamine. This research also suggests that theoretical results may be useful for the rapid detection of food containing trimethylamine.

Synthesis, characterization, and electrochemical properties of a first-row metal phthalocyanine series

A first-row metal phthalocyanine series is synthesized and the effects of axial metal-ligand substitution is investigated electrochemically and in the context of charge carriers for redox-flow batteries.