Mechanism Insight into Direct Amidation Catalyzed by Zr Salts: Evidence of Zr Oxo Clusters as Active Species.

The capricious reactivity and speciation of earth-abundant metals (EAM) hinder the mechanistic understanding essential to boost their efficiency and versatility in catalysis. Moreover, metal's solution chemistry and reactivity are conventionally controlled using organic ligands, while their fundamental chemistry in operando conditions is often overlooked. However, in this study, we showcase how a better understanding of in operando conditions may result in improved catalytic reactions.

Phosphoester bond hydrolysis by a discrete zirconium-oxo cluster: mechanistic insights into the central role of the binuclear Zr-Zr active site.

Effective degradation of non-natural phosphate triesters (PTs) widely used in pesticides and warfare agents is of paramount relevance for human and environmental safety, particularly under acidic conditions where they are highly stable. Here, we present a detailed reactivity and mechanistic study pioneering discrete {ZrO} clusters, which are commonly employed as building blocks for Zr-MOFs and as non-classical soluble coordination compounds for the degradation of PTs using the pesticide ethyl paraoxon as a model. Combined computational studies, mechanistic experiments, and EXAFS analysis show that the reactivity of these clusters arises from their Zr-Zr bimetallic sites, which hydrolyze ethyl paraoxon under acidic conditions through an intramolecular pathway.

Reactive Force Field Development for Propane Dehydrogenation on Platinum Surfaces.

Propane dehydrogenation (PDH) is an on-purpose catalytic technology to produce propylene from propane that operates at high temperatures, 773-973 K. Several key industry players have been active in developing new catalysts and processes with improved carbon footprint and economics, where Pt-based catalysts have played a central role. The optimization of these catalytic systems through computational and atomistic simulations requires large-scale models that account for their reactivity and dynamic properties.

Remote 1,4-Carbon-to-Carbon Boryl Migration: From a Mechanistic Challenge to a Valuable Synthetic Application of Bicycles.

The present paper reports a remote carbon-to-carbon boryl migration via an intramolecular 1,4-B/Cu shift, which establishes an in situ stereospecific electrophilic trap on the alkene moiety. The synthetic application is developed to prepare functionalized cyclopentenes by means of a palladium-catalyzed regioselective intramolecular coupling that completes a strategic cyclopropanation and generates valuable structural bicyclic systems. The mechanism is characterized by DFT (density functional theory) calculations which showed that the 1,4-migration proceeds through an intramolecular, nucleophilic attack of the copper-alkyl moiety on the boron atom bonded to the C(sp), leading to a 5-membered boracycle structure.

Resolving the Mechanism for HO Decomposition over Zr(IV)-Substituted Lindqvist Tungstate: Evidence of Singlet Oxygen Intermediacy.

The decomposition of hydrogen peroxide (HO) is the main undesired side reaction in catalytic oxidation processes of industrial interest that make use of HO as a terminal oxidant, such as the epoxidation of alkenes. However, the mechanism responsible for this reaction is still poorly understood, thus hindering the development of design rules to maximize the efficiency of catalytic oxidations in terms of product selectivity and oxidant utilization efficiency. Here, we thoroughly investigated the HO decomposition mechanism using a Zr-monosubstituted dimeric Lindqvist tungstate, (BuN)[{WOZr(μ-OH)}] (), which revealed high activity for this reaction in acetonitrile.

Boron-Copper 1,3-Rearrangement: the New Concept Behind the Boryl Migration from C(sp ) in Alkenyl Boranes to C(sp ).

Regioselective borylcupration of borylated skipped (Z)-dienes generates diborylated alkylcopper species that are involved in an intramolecular stereospecific B/Cu 1,3-rearrangement by migration of Bpin moiety from C(sp ) to C(sp ). DFT mechanistic studies showed that boryl migration occurs through the formation of 4-membered boracycle intermediate with a moderate free-energy barrier. Moreover, the use of KOMe forms stable Lewis base adducts with Bpin moieties that blocks the reaction.

Bringing Selectivity in H/D Exchange Reactions Catalyzed by Metal Nanoparticles through Modulation of the Metal and the Ligand Shell.

Ru and Rh nanoparticles catalyze the selective H/D exchange in phosphines using D as the deuterium source. The position of the deuterium incorporation is determined by the structure of the P-based substrates, while activity depends on the nature of the metal, the properties of the stabilizing agents, and the type of the substituent on phosphorus. The appropriate catalyst can thus be selected either for the exclusive H/D exchange in aromatic rings or also for alkyl substituents.

Site-Selective (Z)-α-Borylalkenyl Copper Systems for Nucleophilic Stereodefined Allylic Coupling.

1,1-Diborylalkenes can be transformed into (Z)-skipped dienes through Cu -phosphine catalyzed allylic coupling reactions. The energetically preferred formation of (Z)-α-borylalkenyl copper (I) species and the subsequent nucleophilic attack, explains the stereoselective nucleophilic substitution with allyl bromides. The eventual treatment of (Z)-skipped dienes with NaO Bu promotes cyclization/aromatization patterns via enyne intermediates.

Effective Storage of Electrons in Water by the Formation of Highly Reduced Polyoxometalate Clusters.

Aqueous solutions of polyoxometalates (POMs) have been shown to have potential as high-capacity energy storage materials due to their potential for multi-electron redox processes, yet the mechanism of reduction and practical limits are currently unknown. Herein, we explore the mechanism of multi-electron redox processes that allow the highly reduced POM clusters of the form {MO} to absorb electrons in aqueous solution, focusing mechanistically on the Wells-Dawson structure X[PWO], which comprises 18 metal centers and can uptake up to 18 electrons reversibly ( = 18) per cluster in aqueous solution when the countercations are . This unconventional redox activity is rationalized by density functional theory, molecular dynamics simulations, UV-vis, electron paramagnetic resonance spectroscopy, and small-angle X-ray scattering spectra.

Computational Modelling of the Interactions Between Polyoxometalates and Biological Systems.

Polyoxometalates (POMs) structures have raised considerable interest for the last years in their application to biological processes and medicine. Within this area, our mini-review shows that computational modelling is an emerging tool, which can play an important role in understanding the interaction of POMs with biological systems and the mechanisms responsible of their activity, otherwise difficult to achieve experimentally. During recent years, computational studies have mainly focused on the analysis of POM binding to proteins and other systems such as lipid bilayers and nucleic acids, and on the characterization of reaction mechanisms of POMs acting as artificial metalloproteases and phosphoesterases.

N═N Bond Cleavage by Tantalum Hydride Complexes: Mechanistic Insights and Reactivity.

The reaction of [TaCpX] (Cp = η-CMe, η-CHSiMe, η-CHMe; X = Cl, Br) with SiHPh resulted in the formation of the dinuclear hydride tantalum(IV) compounds [(TaCpX)(μ-H)], structurally identified by single-crystal X-ray analyses. These species react with azobenzene to give the mononuclear imide complex [TaCpX(NPh)] along with the release of molecular hydrogen. Analogous reactions between the [{Ta(η-CMe)X}(μ-H)] derivatives and the cyclic diazo reagent benzo[]cinnoline afford the biphenyl-bridged (phenylimido)tantalum complexes [{Ta(η-CMe)X}(μ-NCHCHN)] along with the release of molecular hydrogen.

Transborylation of alkenylboranes with diboranes.

Exchange of boryl moieties between alkenylboranes and diboron reagents has been postulated as a stereospecific cross-metathesis pathway with concomitant formation of mixed diboron reagents. DFT calculations propose a mechanism for the stereocontrolled C(sp)-B/B'-B' cross-metathesis with both symmetric and non-symmetric diboron reagents.

Alkoxide activation of tetra-alkoxy diboron reagents in C-B bond formation: a decade of unpredictable reactivity.

Any attempt to facilitate a new generation of C-B bonds represents a useful tool in organic synthesis. In addition, if that approach highlights the nucleophilic character of boryl moieties in the absence of transition metal complexes, the challenge to create new reactive platforms becomes an opportunity. We have been deeply involved in the experimental and theoretical validation of C-B bond formation by means of alkoxide activation of tetra-alkoxy diboron reagents and here is presented a convenient guide to understand the concept and the applications.

Mapping the Electronic Structure and the Reactivity Trends for Stabilized α-Boryl Carbanions.

The chemistry of stabilized α-boryl carbanions shows remarkable diversity, and can enable many different synthetic routes towards efficient C-C bond formation. The electron-deficient, trivalent boron center stabilizes the carbanion facilitating its generation and tuning its reactivity. Here, the electronic structure and the reactivity trends of a large dataset of α-boryl carbanions are described.

Peptide Hydrolysis by Metal (Oxa)cyclen Complexes: Revisiting the Mechanism and Assessing Ligand Effects.

The mechanism responsible for peptide bond hydrolysis by Co(III) and Cu(II) complexes with (oxa)cyclen ligands has been revisited by means of computational tools. We propose that the mechanism starts by substrate coordination and an outer-sphere attack on the amide C atom of a solvent water molecule assisted by the metal hydroxo moiety as a general base, which occurs through six-membered ring transition states. This new mechanism represents a more likely scenario than the previously proposed mechanisms that involved an inner-sphere nucleophilic attack through more strained four-membered rings transition states.

Consecutive borylcupration/C-C coupling of γ-alkenyl aldehydes towards diastereoselective 2-(borylmethyl)cycloalkanols.

Copper(i) catalyzes the borylative cyclization of γ-alkenyl aldehydes through chemo- and regioselective addition of Cu-B to C[double bond, length as m-dash]C and concomitant intramolecular 1,2-addition of Cu-C on C[double bond, length as m-dash]O. The products are formed in an exclusive diastereoselective manner and computational analysis identifies the key points for the observed chemo- and diastereoselectivity.

Structure-Activity Relationships for the Affinity of Chaotropic Polyoxometalate Anions towards Proteins.

The influence of the composition of chaotropic polyoxometalate (POM) anions on their affinity to biological systems was studied by means of atomistic molecular dynamics (MD) simulations. The variations in the affinity to hen egg-white lysozyme (HEWL) were analyzed along two series of POMs whereby the charge or the size and shape of the metal cluster are modified systematically. Our simulations revealed a quadratic relationship between the charge of the POM and its affinity to HEWL as a consequence of the parabolic growth of POM⋅⋅⋅water interaction with the charge.

A Bridging bis-Allyl Titanium Complex: Mechanistic Insights into the Electronic Structure and Reactivity.

Treatment of the dinuclear compound [{Ti(η-CMe)Cl}(μ-O)] with allylmagnesium chloride provides the formation of the allyltitanium(III) derivative [{Ti(η-CMe)(μ-CH)}(μ-O)] (), structurally identified by single-crystal X-ray analysis. Density functional theory (DFT) calculations confirm that the electronic structure of is a singlet state, and the molecular orbital analysis, along with the short Ti-Ti distance, reveal the presence of a metal-metal single bond between the two Ti(III) centers. Complex reacts rapidly with organic azides, RN (R = Ph, SiMe), to yield the allyl μ-imido derivatives [{Ti(η-CMe)(CHCH═CH)}(μ-NR)(μ-O)] [R = Ph(), SiMe()] along with molecular nitrogen release.

9-Cobalt(II)-Containing 27-Tungsto-3-germanate(IV): Synthesis, Structure, Computational Modeling, and Heterogeneous Water Oxidation Catalysis.

The 9-cobalt(II)-containing trimeric, cyclic polyanion [Co(OH)(HO)(PO)(GeWO)] () was synthesized in an aqueous phosphate solution at pH 8 and isolated as a hydrated mixed sodium-cesium salt. Polyanion was structurally and compositionally characterized in the solid state by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, as well as thermogravimetric and elemental analyses. The magnetic and electrochemical properties of were also studied and compared with those of its phosphorus analogue, [Co(OH)(HO)(HPO)(PWO)] ().

Transition-Metal-Free Allylic Borylation of 1,3-Dienes.

This work explains the reactivity of diboron reagents with 1,3-dienes in a transition-metal-free context. The sole addition of NaCO (30 mol %) to bis(pinacolato)diboron in MeOH allows the 1,4-hydroboration of cyclic and noncyclic 1,3-dienes. The electronic influence on the substrate guarantees the conjugated 1,4-hydroboration versus 1,2-diboration.

How Does the Redox State of Polyoxovanadates Influence the Collective Behavior in Solution? A Case Study with [I@VO] ( q = 3, 5, 7, 11, and 13).

A series of stable reduction-oxidation states of the cagelike [I@V VO] polyoxovanadate (POV) with x = 8, 10, 12, 16, and 18 were studied with density functional theory and molecular dynamics to gain insight into the structural and electron distribution characteristics of these metal-oxo clusters and to analyze the charge/redox-dependent assemblage processes in water and acetonitrile (MeCN) solutions. The calculations show that the interplay between the POV redox state (molecular charge) and the solvent polarity, countercation size, and hydrophilicity (or hydrophobicity) controls the POV agglomeration phenomena, which substantially differ between aqueous and MeCN media. In MeCN, agglomeration is more pronounced for intermediate-charged POVs, whereas in water, the lowest-charged POVs and organic countercations tend to agglomerate into a microphase.

Modeling the Oxygen Vacancy at a Molecular Vanadium(III) Silica-Supported Catalyst.

Here we report on the use of a silanol-decorated polyoxotungstate, [SbWO( BuSiOH)] (1), as a molecular support to describe the coordination of a vanadium atom at a single-site on silica surfaces. By reacting [V(Mes)·thf] (Mes = 2,4,6-trimethylphenyl) with 1 in tetrahydrofuran, the vanadium(III) derivative [SbWO( BuSiO)V(thf)] (2) was obtained. Compound 2 displays the paramagnetic behavior expected for a d-V high spin complex (SQUID measurements) with a triplet electronic ground state (ca.

Transition-Metal-Free Stereoselective Borylation of Allenamides.

Complete stereocontrol on the transition-metal-free hydroboration of the distal double bond of allenamides could be achieved when allenamides contained acetyl substituents, which provided exclusively the Z-isomer. The consecutive Pd-catalyzed cross-coupling reaction allowed the straightforward formation of trisubstituted enamides, with total control of the stereoselectivity.

Self-assembly study of nanometric spheres from polyoxometalate-phenylalanine hybrids, an experimental and theoretical approach.

Herein, we report on the study of supramolecular assemblies based on polyoxometalates (POMs) upon their modification with amino acids. Two POM-amino acid hybrids were synthesized by coupling a functionalized Keggin type polyoxoanion [PW11O39{Sn(C6H4)C[triple bond, length as m-dash]C(C6H4)COOH}]4- with carboxyl-protected (methyl-ester) phenylalanine or diphenylalanine peptides. Surprisingly, all compounds, including the initial POM, formed supramolecular nanospheres in different solvent mixtures, which were examined by scanning electron microscopy (SEM).