Soluble Metal Complexes Research Articles

Study on the synergistic mechanism of sulfuric acid and ammonium sulfate on the extraction of metals from ferronickel slag by roasting

Due to the complex occurrence state of valuable metals in ferronickel slag, the metal extraction rate of the ammonium sulfate roasting process is insufficient. This study proposes a more cost-effective strategy to extract ferronickel slag valuable metals by mixed roasting with sulfuric acid and ammonium sulfate. The effects of the reagent dosage, roasting temperature and roasting time on the metal extraction rate of (NH4)2SO4 roasting, H2SO4 roasting and (NH4)2SO4 and H2SO4 mixed roasting were compared and analyzed. XRD, SEM and TG-DSC were used to reveal the mechanism of mixed roasting to optimize the metal extraction effect from ferronickel slag. The results showed that mixed roasting with a mass ratio of ammonium sulfate to sulfuric acid of 1:1 could reduce the dosage of ammonium sulfate roasting by 2.5 times, and the leaching rates of valuable metals Mg, Fe, Al and Cr increased by 17.46%, 42.8%, 26.06% and 24.89%, respectively. Likewise, comparing to sulfuric acid roasting, the acid consumption of mixed roasting was reduced by two-thirds, and the metal leaching rate was increased by 10.08%, 12.98%, 18.76% and 45.18%, respectively. The “synergistic” mechanism of sulfuric acid and ammonium sulfate on metal extraction by roasting is as follows: ① Before roasting, sulfuric acid partially destroys the surface structure of ferronickel slag particles, forming more pores and channels, creating conditions for the rapid diffusion of ammonium sulfate and sulfuric acid into the slag particles. ② Sulfuric acid reacts with ammonium sulfate to form NH4HSO4, which is more acidic and can accelerate conversion to soluble metal complexes. ③ The addition of sulfuric acid greatly advances the initial temperature of the reaction between ammonium sulfate and metals, widening the temperature range of sulfation roasting and reducing the difficulty of the reaction between ammonium sulfate and metals in ferronickel slag. ④ The liquid–solid reaction increases the reaction interface, improves the mass and heat transfer efficiency and enhances the degree of metal acidification.

The Fast Formation of a Highly Active Homogeneous Catalytic System upon the Soft Leaching of Pd Species from a Heterogeneous Pd/C Precursor

Understanding the interface between soluble metal complexes and supported metal particles is important in order to reveal reaction mechanisms in a new generation of highly active homogeneous transition metal catalysts. In this study, we show that, in the case of palladium forming on a carbon (Pd/C) catalyst from a soluble Pd(0) complex Pd2dba3, the nature of deposited particles on a carbon surface turns out to be much richer than previously assumed, even if a very simple experimental procedure is utilized without the use of additional reagents and procedures. In the process of obtaining a heterogeneous Pd/C catalyst, highly active “hidden” metal centers are formed on the carbon surface, which are leached out by the solvent and demonstrate diverse reactivity in the solution phase. The results indicate that heterogeneous catalysts may naturally contain trace amounts of molecular monometallic centers of a different nature by easily transforming them to the homogeneous catalytic system. In line with a modern concept, a heterogenized homogeneous catalyst precursor was found to leach first, leaving metal nanoparticles mostly intact on the surface. In this study, we point out that the previously neglected soft leaching process contributes to high catalyst activity. The results we obtained demand for leaching to be reconsidered as a flexible tool for catalyst construction and for the rational design of highly active and selective homogeneous catalytic systems, starting from easily available heterogeneous catalyst precursors.

Single Atom and Metal Cluster Catalysts in Organic Reactions: From the Solvent to the Solid

AbstractThe supporting of pre‐formed soluble metal catalysts on solids is a typical methodology to transform soluble but unrecoverable metal complexes into recoverable and reusable solid catalysts. However, this methodology has been barely implemented for ligand‐less, bare single metal atoms (SMAs) and nanoclusters (NCs) in organic synthesis, despite these ultrasmall species can be formed in‐situ during reaction and be the truly catalytic species. The aim of this review is to explore how to speciate active single metal atoms and clusters during homogeneous catalysis (in solution), without ligands, and to prepare them independently, to be transferred to solid supports and catalyze organic reactions. In many cases, the translation to solids gives single atom catalysts (SACs). Supporting of ultrasmall metal aggregates gives more stable, reusable and, sometimes, chemoselective catalysts for representative organic reactions.

Revisiting the TCNQF40/1−/2− Catalysis Mechanism for the [Fe(CN)6]3−/4−‐S2O32−/S4O62− Redox Reaction

Published data suggest that sparingly soluble metal complexes of , where n=0, 1, 2, 4, can act as heterogeneous catalysts for the kinetically very slow - / reaction in aqueous solution. This study shows that the coordination polymer , participates as a homogeneous catalyst via an extremely small concentration of dissolved . This finding suggests that the generally accepted mechanism of catalysis by based solids needs to be revisited to ascertain the role of homogeneous pathways. In the present study, UV-visible spectrophotometry was used to examine the catalysis of the aqueous redox reaction of (1.0 mM) with (100 mM) in the presence of (i) a precursor catalyst, ; (ii) the catalyst, , as the water soluble Li+ salt; and (iii) . A homogeneous reaction scheme that utilises the couple is provided. In the case of derived from highly soluble , quantitative conversion of 1.0 mM to 0.50 mM occurs with complete reduction of to being rapidly accelerated by sub-micomolar concentrations of . generated in the catalytic cycle, reacts with to reform and produce . Along with the rapid catalytic reaction, the sluggish competing reaction between and occurs to give , which is protonated to , along with a trace amount of . On addition of the precursor catalyst, , rapid reduction with occurs to form - the active catalyst. added to water is shown to be sufficiently soluble to provide adequate to act as the catalyst for the - / reaction.

Mechanism of real-time capture of organics by in-situ-formed microbubble flocs to enhance organics removal in hybrid ozonation-coagulation process

The over-oxidation of organic pollutants by pre-ozonation leads to a decreased removal efficiency of coagulation. In this study, it was demonstrated that organics modified by ozonation can be captured in real time by microbubble flocs mediated by the interaction among ozone, Al species, and other organics using the hybrid ozonation-coagulation (HOC) process, which avoids further oxidation of the modified organics. Compared with the pre-ozonation-coagulation process, this real-time capture strategy during the HOC process can increase organics removal efficiency, and broaden the ozone dosing range. The synergistic effect of Al species and ozone enhanced hydroxyl radicals (·OH) formation, which increased the content of carboxyl and hydroxyl groups in the modified intermediates while retaining their original macro aromatic structure. That modified intermediates can be captured and complexed by Al species in the HOC process in real time was verified by differential absorbance spectroscopy (DAS). Al species are complexed with carboxyl and hydroxyl groups of organic compounds to form Al-organic complexes that have COAl coordination bonds. These complex structures protect the modified organic compounds during immediate contact with and decomposition by ozone. The existence of ozone can increase the formation of poly Al species via hydroxyl bridges, thus causing the soluble small-scale metal complex to form insoluble flocs. The surface of flocs can be oxidized and modified, thus strengthening the surface coordination of residual organics in water and further improving their removal efficiency.

High temperature corrosion in various grades of vegetable and waste oils used for bio-fuel production

Corrosion experiments were conducted at 220 °C in vegetable and waste oils used to produce biofuels. Industrial oils and model solutions with controlled concentrations of free fatty acids (FFA) were used. Corrosion of carbon steel and low alloy steel increased with FFA concentration up to several millimeters per year. AISI 316 L stainless steel was immune to corrosion in all FFA concentrations used in this study. Test solution analysis with various techniques allowed identifying corrosion mechanisms involving consumption of FFAs and the formation of highly soluble metal complexes.

Comparative assessment of heterogeneous and homogeneous Suzuki-Miyaura catalytic reactions using bio-Profiles and bio-Factors

Transition metals are essential for most catalytic systems in fine organic synthesis. The usage of transition metals has traditionally raised concerns about their toxicity and potential environmental pollution problems. In this context, the issue of preference for supported catalysts, which can be easily removed from the reaction mixture, over metal complex catalysts is of significant relevance. In this work, we used bio-Profiles and bio-Factors of chemical reactions to assess the impact of catalyst type on the toxicity of a reaction system in the practically important Suzuki-Miyaura reaction. The supported catalysts had noticeably lower cytotoxicity than soluble metal complex catalysts. However, the combined effect of supported catalysts on the environment can depend on their preparation procedure and may have a noticeable “neglected” biological impact. Both types of catalysts made no significant contribution to the “overall toxicity” of the systems studied, while common and typically ignored byproducts demonstrated significantly higher “overall” biological influence. In the present study, we describe how to use bio-Profiles in order to visualize and analyze the biological properties of different types of catalytic reactions.

Activation of Aryl Chlorides in the Suzuki-Miyaura Reaction by “Ligand-Free” Pd Species through a Homogeneous Catalytic Mechanism: Distinguishing between Homogeneous and Heterogeneous Catalytic Mechanisms

A distinction between the homogeneous and heterogeneous catalytic mechanisms of a myriad of Pd catalytic systems for the Suzuki-Miyaura reaction has been made based on soluble metal complexes or he...

Column Experiment for the Removal of Cadmium, Copper, Lead and Zinc from Artificially Contaminated Soil using EDTA, Rhamnolipids, and Soapnut

Environmental contamination caused by high contents of toxic metals in the soil is a global concern. Soil washing using chelating agents and saponin can enhance metal removal from contaminated soils through the formation of soluble metal complexes, mobilization, and extraction with the washing solutions. Column experiments were conducted in this study to assess the feasibility of using a chelate (EDTA), a saponin (soapnut) and microbial (rhamnolipid) cleaning agents to enhance the removal of Cd, Cu, Pb and Zn from sandy loam contaminated soils. The cumulative removal of Cd after 10 pore volumes were 74.05 for EDTA, 63.08 for rhamnolipids, and 69.07 for soapnut. The cumulative removals of Cu after washing with 10 pore volumes were 64.72% for soapnut, 61.58% for rhamnolipids and 61.95% for EDTA. Also, the cumulative removals of Pb were 62% for soapnut, 59.65% for rhamnolipids and 59.95% for EDTA after washing with 10 pore volumes. The cumulative removals of Zn after washing with 10 pore volumes were 68.54% for soapnut, 62.65% for rhamnolipids and 66.08% for EDTA. The performance of these experiments demonstrates that the application of these cleaning agents in in-situ soil remediation can be effective alternative to ex-situ remediation.

Heterogeneous polymer supported and soluble tantalum metal complex catalysts for acylation reaction: A kinetic study

New soluble and insoluble Tantalum pentachloride complex catalysts are prepared by simple procedures using pyridine and polymer-supported cross-linked (poly-4-vinyl pyridine) beads (PSCPVP) respectively as supports and Tantalum pentachloride as a catalytic moiety (TaCl5). The prepared soluble Py-TaCl5 and insoluble bead-shaped PSCPVP-TaCl5 catalysts have been characterized with FT-IR, UV-Vis, SEM, TGA and elemental analysis techniques. The catalytic efficiency of these catalysts has been examined through acylation of ethanol as a model reaction under identical pseudo first order reaction condition. From the calculated kobs values, it has been noticed that both the catalysts are active and however, Py-TaCl5shown 1.65 fold has increased activity (kobs =11.42x103 min-1) than insoluble PSCPVP-TaCl5 catalyst (kobs= 6.98x103, min-1). Although, PSCPVP-TaCl5 has shown lesser activity than soluble due to its lower cost, recyclability and reusable nature up to third cycle, it has received greater recognition. Hence, in order to utilize this insoluble bead-shaped PSCPVP-TaCl5 catalyst to pack in column reactor and to carry out the same reaction for continuous mode operation at industrial level, detailed kinetics study for acylation of ethanol has been conducted under pseudo first order condition by varying the different experimental parameters and has observed that each parameter has influenced the reaction. The obtained kobs value reveals that reaction rates increase with the increase in the stirring speed, [substrate], [catalyst] and temperature. The thermodynamic parameters viz., activation energy (Ea), entropy (∆S), enthalpy (∆H) and free energy (∆G#) for the reaction are also calculated for the first time and their observed values are 35.2 kJmol-1, -64.6 kJ-1mol-1, 37.7 kJmol-1and 57.3 kJmol-1 respectively. The prepared insoluble catalyst is stable even after its use for three times in acylation without losing its efficiency, thus it is better suited for industrial applications.

Manganese in the hydrosphere of the Jewish autonomous region: surface water

At present, knowledge about the content of manganese in the surface waters of the Jewish Autonomous Region is becoming more and more relevant, since the development and extraction of iron-manganese ores has already begun in the area of the Bidzhan deposit in the north-west of the region. It is planned to develop iron-manganese deposits in other regions of the autonomy. However, we are not sufficiently aware of the migration of this element, its spread by watercourses along the hydraulic network, the change in the forms of transportation due to the boggy territory of the autonomy, and the possible negative impact on aquatic organisms. The purpose of our work is to study the distribution of manganese in surface watercourses, taking into account the geological features and natural conditions of the Jewish Autonomous Region. The content of total manganese in the surface waters of the Bira River and mainly its northern tributaries located on the territory of the autonomy was determined by the method of atomic absorption spectrophotometry. The article presents the results of determining manganese and iron, as well as indicators that affect their migration ability, in the surface watercourses of the Jewish Autonomous Region for two years. The paper describes and analyzes the natural conditions and geological features of the autonomy that affect the distribution of manganese in its surface waters. As a result of the study, it was revealed that all rivers reflect the specific nature of the natural conditions of their formation. In the watercourses of the northwestern part of the region, draining the foothills of the Small Khingan, the influence of deposits of ferromanganese ores is clearly manifested. In the rivers flowing from the southern spurs of the Bureinsky ridge, manganese ore content is not felt. Bira's sharp turn from the mountainous north to the south, to the Amur, occurs against the background of a contrasting change in the relief and close contact of the river with the adjacent swampy plain. Natural processes and sources of Mn input into river waters change: the input of soluble humid metal complexes from the bog drainage begins.

Comparison of Aβ (1–40, 1–28, 11–22, and 29–40) aggregation processes and inhibition of toxic species generated in early stages of aggregation by a water-soluble ruthenium complex

Neurotoxicity of amyloid beta (Aβ) species generated in early stages of aggregation has been associated with development of Alzheimer's disease (AD). Consequently, the field of action of compounds that can identify and inhibit the formation of these species has enlarged considerably. This study investigates the effect and influence of the luminescent, water soluble metal complex cis-[Ru(phen)2(3,4Apy)2]2+ (RuApy, 3,4Apy = 3,4-diaminopyridine, phen = 1,10-phenanthroline) on the aggregation process and toxicity of Aβ1–40 and its Aβ1–28, Aβ11–22 and Aβ29–40 fragments since their early stages. The absence of correlation between the conformations generated by Aβ fragments and the full length 1–40 peptide during aggregation and the absence of toxicity of Aβ fragments to PC12 cells in all stages of aggregation indicated that the aggregation pathway and toxicity found to the full-length Aβ1–40 depends on specific interactions between the three fragments. The toxicity of Aβ1–40 was dependent on the aggregation step investigated: species generated at the beginning (15 min) of aggregation were toxic, whereas mature (120 min) fibrils were not. The RuApy complex is not toxic to PC12 cells up to 60 μM, and does not interfere with the aggregation pathway of the Aβ fragments, but interferes with the aggregation of Aβ1–40 and protects the PC12 cells, maintaining 100% of cell viability against the toxicity of Aβ1–40 species generated in early stages of aggregation.

Ternary Cobalt(II), Nickel(II), and Copper(II) complexes containing metformin and ethylenediamine: Synthesis, characterization, thermal, in vitro DNA binding, in silico molecular docking, and in vivo antihyperglycemic studies

Three new water soluble ternary metal complexes, [Co(metf)(en)2]Cl2(1), [Ni(metf)(en)2]Cl2(2), and [Cu(metf)(en)2]Cl2(3), (Metf = metformin, en = ethylenediamine), were synthesized and characterized, and pharmacodynamic evaluation was reported. From the spectral analysis, octahedral geometry was proposed to all the three metal complexes. The Kinetic parameters have been determined by thermogravimetric data using Coats‐Redfern method. The stability of the complexes was obtained from their molecular orbital structures from which the quantum chemical parameters were calculated using the highest occupied molecular orbital (HOMO)‐lowest unoccupied molecular orbital (LUMO) energies. The DNA binding studies of these complexes were explored by absorption, emission, and viscosity. Groove mode of surface binding of these complexes with DNA was explained by viscosity studies. Nuclease activity exhibited by these complexes on pUC19 DNA was experimented by agarose gel electrophoresis. Discovery Studio 2.1 software was used for docking studies of these complexes into B‐DNA sequence, 5′(D*AP*CP*CP*GP*AP*CP*GP*TP*CP*GP*GP*T)‐3′ retrieved from protein data bank (PDB ID: 423D). The maximum score is seen for complex 1. The antihyperglycemic activity of these complexes was studied in streptozotocin (STZ)‐diabetic rats. The substantial increase in the antihyperglycemic activity of the complexes is seen when compared with pure drug. The maximum antihyperglycemic activity is recorded for complex 1.

Novel water soluble Schiff base metal complexes: Synthesis, characterization, antimicrobial-, DNA cleavage, and anticancer activity

The Schiff base ligand, 4-nitrobenzaldehyde-glycylglycine (4-NBA-GG) and its Co(II), Ni(II), Cu(II), and Zn(II) complexes were synthesized and characterized by elemental analysis, mass, NMR, IR, electronic spectra, magnetic moment, molar conductance, ESR, CV, TGA, and powder XRD. All the complexes were found to be soluble in water. According to the spectral analysis, the 4-NBA-GG acts as a tridentate monobasic donor coordinating through the azomethine nitrogen, carboxylato oxygen and deprotonated peptide nitrogen atoms. The geometrical structures of these complexes are found to be octahedral. Antimicrobial studies of the synthesized compounds were evaluated and reported. The DNA cleavage activities were assayed against E. coli DNA, besides, anticancer activities was also studied towards human Colon Cancer Cells (HCT116) and cervical cancer cell line (HeLa). The obtained results showed that the complexes, especially Cu(II) and Zn(II) complexes strongly interact with E. coli DNA and active against both cancer cells.

Comparative Activation Process of Pb, Cd and Tl Using Chelating Agents from Contaminated Red Soils.

Adding chelating agents is a critical technique of heavy metal activation for enhancing phytoextraction through the formation of soluble metal complexes which will be more readily available for extraction. The preliminary, dynamic, equilibrium activation experiments and speciation analysis of Pb, Cd and Tl in contaminated red soils were used to select six chelates with relatively good activation performance from nine chelates, and the effects of dosage and pH on the heavy metals activation were studied systematically. Results showed that the activation of Pb, Cd and Tl by chelates reached equilibrium within 2 h, and the activation process showed three stages. Under neutral conditions, chelates had better activation performance on Pb- and Cd-contaminated soils. Except for S,S-ethylenediamine disuccinic acid (S,S-EDDS) and citric acid (CA), the maximum equilibrium activation effect (MEAE) of ethylenediaminetetraacetic acid (EDTA), N,N-bis (carboxymethyl) glutamic acid (GLDA), diethylenetriaminepentaacetic acid (DTPA) and aminotriacetic acid (NTA) was over 81%. The MEAE of Tl-contaminated soil was less than 15%. The decreasing order of the dosage of chelating agents corresponding to MEAE for three types of contaminated soils was Pb-, Cd- and Tl-contaminated soil, relating to the forms of heavy metals, the stability constants of metal–chelates and the activation of non-target elements Fe in red soil. Under acidic conditions, the activation efficiencies of chelates decreased to differing degrees in Pb- and Cd-contaminated soils, whereas the activation efficiencies of chelating agents in Tl-contaminated soils were slightly enhanced.

A Stand‐Alone Module for Solar‐Driven H2 Production Coupled with Redox‐Mediated Sulfide Remediation

Efficient electrochemical devices are required to convert electric power by intermittent renewable energy sources into a chemical form. The choice of combination in reduction–oxidation reactions can vary depending on the target, which provides different thermodynamics and kinetics. A promising approach for H2 production coupled with sulfide remediation is demonstrated to utilize the intermediate redox media. H2 is produced on the cathode, and soluble redox ions in a reduced form are oxidized on the anode. The ions are then transferred to a separate reactor to oxidize the sulfide ions via a homogeneous reaction, and the reduced redox ions are recirculated. A solar‐driven redox photovoltaic‐electrochemical (PV‐EC) system is operated as a stand‐alone module and is composed of Cu(In,Ga)(S,Se)2 (CIGS) PVs and EC cells in series and operated under natural solar irradiation. A unique EC cell is established in an aqueous‐phase membraneless configuration at ambient temperature, and a cathode is decorated with a semipermeable CrOx‐based nanomembrane. This allows for selective H2 evolution without causing Fe redox reduction. Remaining issues associated with the stability of the CrOx permselective layer on the cathode are also discussed, which are associated with the formation constant of a soluble metal complex in the presence of ligand counterions.

The Multifaceted Reactivity of Single-Atom Heterogeneous Catalysts.

Single-atom heterogeneous catalysts (SACs) attached to carefully chosen hosts are attracting considerable interest; principally because they offer maximum utilization per metal atom and are usually readily recyclable. However, diminution of the atomic population of nanoparticles or nanoclusters to single atoms can significantly alter reactivity because of the consequent changes in the active-site structure. By examining various diverse applications, we ascertain whether the performance of SACs is enhanced or suppressed. We also note that SACs generally display unique kinds of catalytic cycles. The choice of host is crucial since it influences both the electronic and steric environment of the metal center. Moreover, it may function as a cocatalyst. All these aspects impact upon the design of new SACs, which exhibit similarities to hetero- and homogeneous predecessors. Additionally, SACs offer a viable replacement of soluble metal complexes in processes that remain difficult to heterogenize.

A heterogeneous single-atom palladium catalyst surpassing homogeneous systems for Suzuki coupling.

Palladium-catalysed cross-coupling reactions, central tools in fine-chemical synthesis, predominantly employ soluble metal complexes despite recognized challenges with product purification and catalyst reusability1-3. Attempts to tether these homogeneous catalysts on insoluble carriers have been thwarted by suboptimal stability, which leads to a progressively worsening performance due to metal leaching or clustering4. The alternative application of supported Pd nanoparticles has faced limitations because of insufficient activity under the mild conditions required to avoid thermal degradation of the substrates or products. Single-atom heterogeneous catalysts lie at the frontier5-18. Here, we show that the Pd atoms anchored on exfoliated graphitic carbon nitride (Pd-ECN) capture the advantages of both worlds, as they comprise a solid catalyst that matches the high chemoselectivity and broad functional group tolerance of state-of-the-art homogeneous catalysts for Suzuki couplings, and also demonstrate a robust stability in flow. The adaptive coordination environment within the macroheterocycles of ECN facilitates each catalytic step. The findings illustrate the exciting opportunities presented by nanostructuring single atoms in solid hosts for catalytic processes that remain difficult to heterogenize.

Metal leaching from refinery waste hydroprocessing catalyst

ABSTRACTThe present study aims to develop an eco-friendly methodology for the recovery of nickel (Ni), molybdenum (Mo), and vanadium (V) from the refinery waste spent hydroprocessing catalyst. The proposed process has two stages: the first stage is to separate alumina, while the second stage involves the separation of metal compounds. The effectiveness of leaching agents, such as NH4OH, (NH4)2CO3, and (NH4)2S2O8, for the extraction of Mo, V, Ni, and Al from the refinery spent catalyst has been reported as a function of reagent concentration (0.5 to 2.0 molar), leaching time (1 to 6 h), and temperature (35 to 60°C). The optimal leaching conditions were achieved to obtain the maximum recovery of Mo, Ni, and V metals. The effect of the mixture of multi-ammonium salts on the metal extraction was also studied, which showed an adverse effect for Ni and V, while marginal improvement was observed for Mo leaching. The ammonium salts can form soluble metal complexes, in which stability or solubility depends on the nature of ammonium salt and the reaction conditions. The extracted metals and support can be reused to synthesize a fresh hydroprocessing catalyst. The process will reduce the refinery waste and recover the expensive metals. Therefore, the process is not only important from an environmental point of view but also vital from an economic perspective.

Full-Range Interconversion of Nanocrystals and Bulk Metal with a Highly Selective Molecular Catalyst

Catalysis by soluble metal complexes often encompasses the occurrence of nanoparticles and aggregated inactive states, but the role of the different species is unclear. For the generation of highly active catalysts, it is crucial to know the relations between active and inactive states and the reversibility of such interconversions. This is further complicated by the question of the true nature of the active species, in particular for reactions that use dispersed nanoparticles as a catalyst (precursor), which can interconvert to soluble species. We show that a molecular catalyst can interconnect completely up to the step of bulk metal in an isomerizing methoxycarbonylation converting an unsaturated fatty acid to a linear diester with a very characteristic reactivity. The active species, a diphosphine-coordinated Pd hydride, decomposes to the diprotonated diphosphine ligand and a Pd0 species that agglomerates and precipitates as Pd black. This reaction is completely reversible, as shown for several example...