Search Results (60)

Paddlewheel dirhodium complexes are cytotoxic compounds that are also used as catalysts and in the formation of Rh-based artificial metalloenzymes. Low-temperature structures of adducts formed by the model protein hen egg white lysozyme (HEWL) with dirhodium tetraacetate ([Rh₂(μ-O₂CCH₃)₄]) when crystals of the protein were treated with the metal compound at 20 °C demonstrated that [Rh₂(μ-O₂CCH₃)₄] in part breaks down upon reaction with HEWL; dimeric Rh-Rh units bind the side chains of Asp18 and the C-terminal carboxylate, and monometallic fragments coordinate the side chains of Arg14 and His15 in 20% ethylene glycol, 0.100 M sodium acetate at pH 4.5 and 0.600 M sodium nitrate, while dimeric Rh-Rh units bind the side chains of Asn93 and Lys96, the C-terminal carboxylate and Asp101, with monometallic fragments that bind the side chains of Lys33 and His15 in 0.010 M HEPES pH 7.5 and 2.00 M sodium formate. To verify whether the binding of this metallodrug to proteins also occurs at body temperature, crystals of HEWL were grown in 0.010 M HEPES pH 7.5 and 2.00 M sodium formate at 37 °C and soaked with [Rh₂(μ-O₂CCH₃)₄] at the same temperature. X-ray diffraction data collected on these crystals at 37 °C demonstrate that [Rh₂(μ-O₂CCH₃)₄] reacts with proteins at body temperature. The structures of the Rh/HEWL adduct formed at 20 °C (obtained from data collected at 100 K) and at 37 °C under the same experimental conditions are very similar, with metal binding sites that are conserved. However, metal-containing fragment occupancy is higher in the structure obtained at 37 °C, suggesting a role of temperature in defining the protein metalation process. Full article

Fluorinated organic molecules have become indispensable in modern chemistry, owing to the unique properties imparted by fluorine to other compounds, including enhanced metabolic stability, controlled lipophilicity, and improved bioavailability. The site-selective incorporation of fluorine atoms into organic frameworks is essential in pharmaceutical, agrochemical, and material science research. In recent years, catalytic fluorination has become an important methodology for the efficient and selective incorporation of fluorine atoms into complex molecular architectures. This review highlights advances in catalytic fluorination reactions over the past six years and describes the contributions of transition metal catalysts, photocatalysts, organocatalysts, and electrochemical systems that have enabled site-selective fluorination under a variety of conditions. Particular attention is given to the use of well-defined fluorinating agents, including Selectfluor, N-fluorobenzenesulfonimide (NFSI), AlkylFluor, Synfluor, and hypervalent iodine reagents. These reagents have been combined with diverse catalytic systems, such as AgNO₃, Rh(II), Mo-based complexes, Co(II)-salen, and various organocatalysts, including β,β-diaryl serine catalysts, isothiourea catalysts, and chiral phase-transfer catalysts. This review summarizes proposed mechanisms reported in the original studies and discusses examples of electrophilic, nucleophilic, radical, photoredox, and electrochemical fluorination pathways. Recent developments in stereoselective and more sustainable protocols are also examined. By consolidating these strategies, this article provides an up-to-date perspective on catalytic fluorination and its impact on synthetic organic chemistry. Full article

Strict gaseous emission standards are applied globally to regulate the maximum amounts of pollutant emissions that can be produced from all vehicles. The exhaust aftertreatment systems used by automotive manufacturers rely on the utilization of precious metals (Pt, Pd, Rh). However, much effort has been devoted on the reduction or the replacement of the amount of Platinum Group Metals (PGMs) in three-way catalysts (TWC), both from a cost-effectiveness as well as an environmental point of view. PROMETHEUS catalyst, which was recently homologated for Euro 6 applications, is a low-cost, Cu-based TWC, which consists of a significantly lower quantity of PGMs compared to conventional state-of-the-art catalysts and achieves similar or even better catalytic efficiencies. In this review paper, a complex reaction scheme is proposed for the first time for a catalytic converter utilizing Cu and PGMs, following an extensive literature investigation of the available models. The scheme also accounts for the surface reaction mechanisms of the main processes and the side reactions potentially taking place during the TWC operation in the presence of Cu and at least one of the following PGMs: Pt, Pd or Rh. At a next step, the proposed reaction scheme will be validated based on experimental data, using mathematical modelling of a PROMETHEUS catalytic converter incorporating Cu and PGM nanoparticles. Full article

The development of a selective separation and recovery method for platinum-group metals (PGMs) is in high demand to establish efficient and practical recycling technologies for different secondary materials such as industrial automobile catalysts. In this study, the highly selective precipitation of Pt(IV) from hydrochloric acid (HCl) solutions containing Pd(II), Pt(IV), and Rh(III) was successfully achieved using m-phenylenediamine dihydrochloride (MPDA) as a precipitant. Pt(IV) selectivity was observed at HCl concentrations higher than 7 M, whereas the co-precipitation of Rh(III) could not be suppressed using 3–7 M HCl solutions. Successful recovery of Pt(IV)-containing precipitates with high Pt yield (94.6%) and Pt purity (98.5%) was also achieved using an actual catalyst leaching solution with a complex composition containing PGMs, base metals, and rare metals. Structural analyses revealed that the Pt(IV)-containing precipitate forms ionic crystals composed of [PtCl₆]²⁻/protonated m-phenylenediamine (MPDA-2H⁺) in a 1:1 ratio. The high stability and insolubility of the Pt(IV)-containing ionic crystals, owing to their highly packed structure, resulted in the highly selective precipitation of Pt(IV) at high HCl concentrations. Full article

Four anionic rhodium complexes were synthesized using RhCl₃ as a precursor. All derivatives were isolated and characterized spectroscopically (NMR, ESI-MS). For one of them, [BMPip][RhCl₄], the crystallographic structure was determined. Additionally, their melting points and thermal stabilities were established. The obtained derivatives were used as catalysts for the hydrosilylation of two olefins with various properties. All tested catalysts were insoluble in the reaction medium, which permitted their easy isolation and repeated use in subsequent catalytic cycles. The most effective catalyst did not lose its activity, even after fifty cycles of hydrosilylation of octene using heptamethyltrisiloxane (HMTS). Full article

Water contamination has become a global concern, and the prevalence of complex substances known as emerging contaminants constitute a risk to human health and the environment. This work focused on an innovative approach of integrating sonolysis and photocatalysis to remove a standard textile dye efficiently. A highly photo-active, bismuth ferrite (BiFeO₃) nanocatalyst with single particle sizes between 86 and 265 nm was obtained by a novel one-pot combustion method using a deep eutectic solvent as a precursor. The said catalyst was thoroughly characterized and evaluated for photocatalytic and sono-photocatalytic degradation of rhodamine B (RhB). Photocatalytic experiments were conducted under visible light irradiation (450–600 nm). Sono-photocatalytic (SPC) experiments were conducted, focusing on the influence of operational parameters (frequency, power, and pH) on the degradation performance. High-frequency values of 578, 866, and 1138 kHz were explored to promote cavitation dynamics and reactive species generation, improving removal efficiency. Results demonstrated that when sonolysis and photocatalysis were performed separately, the degradation efficiency ranged between 85 and 87%. Remarkably, when the combined SPC degradation was carried out, the RhB removal reached about 99.9% after 70 min. It is discussed that this behavior is due to the increased generation of OH^• radicals as a product of the cavitation phenomena related to the ultrasound-assisted process. Moreover, it is argued that SPC significantly improves reaction kinetics and mass transfer rates, facilitating catalyst dispersion and contact with the RhB molecules. Finally, the stability of the catalyst was evaluated in five repeated RhB removal cycles, where the activity remained consistently strong. Full article

Addressing the pressing needs for alternatives to fossil fuel-based energy sources, this research explores the intricate interplay between Rhodium (Rh₃) clusters and titanium dioxide (TiO₂) to improve photocatalytic water splitting for the generation of eco-friendly hydrogen. This research applies the density functional theory (DFT) coupled with the Hartree–Fock theory to meticulously examine the structural and electronic structures of Rh₃ clusters on TiO₂ (110) interfaces. Considering the photocatalytic capabilities of TiO₂ and its inherent limitations in harnessing visible light, the potential for metals such as Rh₃ clusters to act as co-catalysts is assessed. The results show that triangular Rh₃ clusters demonstrate remarkable stability and efficacy in charge transfer when integrated into rutile TiO₂ (110), undergoing oxidation in optimal adsorption conditions and altering the electronic structures of TiO₂. The subsequent analysis of TiO₂ surfaces exhibiting defects indicates that Rh₃ clusters elevate the energy necessary for the formation of an oxygen vacancy, thereby enhancing the stability of the metal oxide. Additionally, the combination of Rh₃-cluster adsorption and oxygen-vacancy formation generates polaronic and localized states, crucial for enhancing the photocatalytic activity of metal oxide in the visible light range. Through the DFT analysis, this study elucidates the importance of Rh₃ clusters as co-catalysts in TiO₂-based photocatalytic frameworks, paving the way for empirical testing and the fabrication of effective photocatalysts for hydrogen production. The elucidated impact on oxygen vacancy formation and electronic structures highlights the complex interplay between Rh₃ clusters and TiO₂ surfaces, providing insightful guidance for subsequent studies aimed at achieving clean and sustainable energy solutions. Full article

The discovery that cyclic (ArO)₂PF can support Rh-catalysts for hydroformylation with significant advantages in tuning regioselectivity transformed the study of metal complexes of monofluorophos ligands from one of primarily academic interest to one with potentially important applications in catalysis. In this review, the syntheses of monofluorophosphites, (RO)₂PF, and monofluorophosphines, R₂PF, are discussed and the factors that control the kinetic stability of these ligands to hydrolysis and disproportionation are set out. A survey of the coordination chemistry of these two classes of monofluorophos ligands with d-block metals is presented, emphasising the bonding of the fluorophos to d-block metals, predominantly in low oxidation states. The application of monofluorophos ligands in homogeneous catalysis (especially hydroformylation and hydrocyanation) is discussed, and it is argued that there is great potential for monofluorophos complexes in future catalytic applications. Full article

The hydrogenation of C=C bonds in styrene−butadiene rubber (SBR), catalyzed by RhH(P(i-Pr)₃)₃, was experimentally investigated. Tris(triisopropylphosphine)hydridorhodium(I), RhH(P(i-Pr)₃)₃ (i-Pr=CH(CH₃)₂) was prepared by using rhodium chloride (RhCl₃), tetrahydrofuran (THF), triisopropylphosphine (P(i-Pr)₃) and a sodium mercury amalgam. The effect of catalyst/polymer ratio, reaction temperature, and hydrogen pressure on the reactivity of the catalytic system has been studied. The optimal experimental condition was obtained. The hydrogenated styrene-butadiene rubber (HSBR) was analyzed by FT-IR and ¹H-NMR. In the absence of any additives, the conversion of C=C bonds in SBR could easily reach 95% in a short period of time, and no obvious cross-linking was observed. The dynamic properties of SBR did not change after the hydrogenation of the unsaturated C=C bonds. A preliminary reaction mechanism was also proposed. This study provides a new route, not only for the chemical modification of SBR by using a rhodium complex but also for the hydrogenation of other unsaturated polymers, such as diene-based rubbers. Full article

Water pollution is a serious worldwide problem. Among its pollutants, dyes that are overused by various types of industries and are resistant to conventional effluent treatments stand out. In this study, mixed copper and nickel ferrites Ni_xCu_(1-x)Fe₂O₄ (x = 0, 0.2, 0.4, 0.6, 0.8 e 1.0), were produced by the EDTA-Citrate complexation method, characterized and applied in photocatalysis with methylene blue (MB) and rhodamine B (RhB) dyes, varying the reaction pH between 2, 6 and 10. The ferrites with the highest percentages of copper had a tetragonal structure, while those with the highest percentages of nickel had a cubic structure, all with inverse spinel and all presenting bandgap values lower than 2 eV. Samples with higher percentages of copper (x = 0 and 0.2) at pH 10 showed degradation of approximately 55% for RhB and 40% for MB. A mixture of MB and RhB was also evaluated, showing a greater removal of methylene blue due to its preferential adsorption on the surface of the material. In this way, mixed copper and nickel ferrites proved promising as catalysts in photocatalytic processes. Full article

Triphenylphosphine acetylacetone carbonyl rhodium (ROPAC) is an important catalyst in the petrochemical industry, and its deactivated waste catalyst holds significant value for recovery. This study focuses on the existing forms of rhodium (Rh) in waste catalysts and the current status of traditional processes. A green, efficient, and continuous recovery technique was developed using a sealed stainless steel microchannel reactor. The influence of reaction temperature, reaction time, and phase ratio on the Rh recovery rate was investigated, and the process parameters were optimized using response surface methodology (RSM). The results indicate that the magnitude of the impact on the Rh recovery rate follows the order: reaction temperature > reaction time > phase ratio. The optimized process parameters were determined as follows: a reaction time of 29 min, a reaction temperature of 110 °C, and a phase ratio of 1:1, with a corresponding maximum recovery rate of Rh of 66.06%. Furthermore, secondary treatment was performed on the organic phase after primary recovery using the same process conditions, resulting in an overall Rh recovery rate of 95.6%, indicating satisfactory recovery efficiency. Moreover, the application of FTIR and ICP-OES analysis provided definitive evidence that the oxidative dissociation of the rhodium-phosphine chemical bond by H₂O₂ within ROPAC leads to the conversion of Rh⁺ into Rh³⁺. Subsequently, Rh forms chloroaquorhodium (III) complexes that enter the aqueous phase, enabling effective recovery of Rh. Full article

Diazo compounds are organic substances that are often used as precursors in organic synthesis like cyclization reactions, olefinations, cyclopropanations, cyclopropenations, rearrangements, and carbene or metallocarbene insertions into C−H, N−H, O−H, S−H, and Si−H bonds. Typically, reactions from diazo compounds are catalyzed by transition metals with various ligands that modulate the capacity and selectivity of the catalyst. These ligands can modify and enhance chemoselectivity in the substrate, regioselectivity and enantioselectivity by reflecting these preferences in the products. Porphyrins have been used as catalysts in several important reactions for organic synthesis and also in several medicinal applications. In the chemistry of diazo compounds, porphyrins are very efficient as catalysts when complexed with low-cost metals (e.g., Fe and Co) and, therefore, in recent years, this has been the subject of significant research. This review will summarize the advances in the studies involving the field of diazo compounds catalyzed by metalloporphyrins (M−Porph, M = Fe, Ru, Os, Co, Rh, Ir) in the last five years to provide a clear overview and possible opportunities for future applications. Also, at the end of this review, the properties of artificial metalloenzymes and hemoproteins as biocatalysts for a broad range of applications, namely those concerning carbene-transfer reactions, will be considered. Full article

A visible-light-active photocatalyst, SnP/AA@TiO₂, was fabricated by utilizing the coordination chemistry between the axial hydroxo-ligand in the (trans-dihydroxo)(5,10,15,20-tetraphenylporphyrinato)Sn(IV) complex (SnP) and adipic acid (AA) on the surface of TiO₂ nanoparticles. The SnP center was strongly bonded to the surface of the TiO₂ nanoparticles via the adipic acid linkage in SnP/AA@TiO₂, as confirmed by various instrumental techniques. SnP/AA@TiO₂ exhibited remarkably enhanced photocatalytic activity toward the degradation of rhodamine B dye (RhB) in aqueous solution under visible-light irradiation. The RhB degradation efficiency of SnP/AA@TiO₂ was 95% within 80 min, with a rate constant of 0.0366 min⁻¹. The high degradation efficiency, low catalyst loading and high reusability make SnP-anchored photocatalysts more efficient than other photocatalysts, such as TiO₂ and SnP@TiO₂. Full article

In this study, we proposed photocatalysts based on graphite-like carbon nitride with a low content (0.01–0.5 wt.%) of noble metals (Pd, Rh) for hydrogen evolution under visible light irradiation. As precursors of rhodium and palladium, labile aqua and nitrato complexes [Rh₂(H₂O)₈(μ-OH)₂](NO₃)₄∙4H₂O and (Et₄N)₂[Pd(NO₃)₄], respectively, were proposed. To obtain metallic particles, reduction was carried out in H₂ at 400 °C. The synthesized photocatalysts were studied using X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy and high-resolution transmission electron microscopy. The activity of the photocatalysts was tested in the hydrogen evolution from aqueous and aqueous alkaline solutions of TEOA under visible light with a wavelength of 428 nm. It was shown that the activity for the 0.01–0.5% Rh/g-C₃N₄ series is higher than in the case of the 0.01–0.5% Pd/g-C₃N₄ photocatalysts. The 0.5% Rh/g-C₃N₄ sample showed the highest activity per gram of catalyst, equal to 3.9 mmol g_cat^–1 h^–1, whereas the most efficient use of the metal particles was found over the 0.1% Rh/g-C₃N₄ photocatalyst, with the activity of 2.4 mol per gram of Rh per hour. The data obtained are of interest and can serve for further research in the field of photocatalytic hydrogen evolution using noble metals as cocatalysts. Full article

The preparation of ammine complexes of transition metals having oxidizing anions such as permanganate and perrhenate ions is a great challenge due to possible reactions between ammonia and oxidizing anions during the synthesis of these materials. However, it has an important role in both the development of new oxidants in organic chemistry and especially in the preparation of mixed-metal oxide catalyst precursors and metal alloys for their controlled temperature decomposition reactions. Therefore, in this paper, synthetic procedures to prepare ammonia complexes of transition metal permanganate, pertechnetate, and perrhenate (the VIIB group tetraoxometallates) salts have been comprehensively reviewed. The available data about these compounds’ structures and spectroscopic properties, including the presence of hydrogen bonds that act as redox reaction centers during thermal decomposition, are given and evaluated in detail. The nature of the thermal decomposition products has also been summarized. The available information about the role of the ammine complexes of transition metal permanganate salts in organic oxidation reactions, such as the oxidation of benzyl alcohols and regeneration of oxo-compounds from oximes and phenylhydrazones, including the kinetics of these processes, has also been collected. Their physical and chemical properties, including the thermal decomposition characteristics of known diammine (Ag(I), Cd, Zn, Cu(II), Ni(II)), triammine (Ag(I)), and simple or mixed ligand tetraammine (Cu(II), Zn, Cd, Ni(II), Co(II), Pt(II), Pd(II), Co(III)), Ru(III), pentaammine (Co(III), Cr(III), Rh(III) and Ir(III)), and hexaammine (Ni(II), Co(III), Cr(III)) complexes of transition metals with tetraoxometallate(VII) anions (M = Mn, Tc and Re), have been summarized. The preparation and properties of some special mixed ligand/anion/cation-containing complexes, such as [Ru(NH₃)₄(NO)(H₂O)](ReO₄)₂, [Co(NH₃)₅(H₂O)](ReO₄)₂, [Co(NH₃)₅X](MnO₄)₂ (X = Cl, Br), [Co(NH₃)₆]Cl₂(MnO₄), [Co(NH₃)₅ReO₄]X₂ (X = Cl, NO₃, ClO₄, ReO₄), and K[Co(NH₃)₆]Cl₂(MnO₄)₂, are also included. Full article