Activation and Functionalization of the Uranyl Ion by Electrochemical Reduction.

Interconversion of the oxidation states of uranium enables separations and reactivity schemes involving this element and contributes to technologies for recycling of spent nuclear fuels. The redox behaviors of uranium species impact these processes, but use of electrochemical methods to drive reactions of molecular uranium complexes and to obtain molecular insights into the outcomes of electrode-driven reactions has received far less attention than it deserves. Here, we show that electro-reduction of the uranyl ion (UO) can be used to promote stepwise functionalization of the typically unreactive oxo groups with exogenous triphenylborane (BPh) serving as a moderate electrophile, avoiding the conventional requirement for a chemical reductant.

Vanadium Substitution Dictates H Atom Uptake at Lindqvist-type Polyoxotungstates.

Understanding how modification of molecular structures changes the thermochemistry of H atom uptake can provide design criteria for the formation of highly active catalysts for reductive transformations. Herein, we describe the effect of doping an atomically precise polyoxotungstate with vanadium on proton-coupled electron transfer (PCET) reactivity. The Lindqvist-type polyoxotungstate [WO] displays reversible redox chemistry, which was found to be unchanged in the presence of acid, indicating an inability to couple reduction with protonation.

Effective Alkyl-Alkyl Cross-Coupling with an Iron-Xantphos Catalyst: Mechanistic and Structural Insights.

While iron-catalyzed C(sp)-C(sp) cross-couplings have been widely studied and developed in the last decade, alkyl-alkyl cross-coupling systems with iron remain underdeveloped despite the importance of C(sp)-C(sp) bonds in organic synthesis. A major challenge to the development of these reactions is the current lack of fundamental insight into ligand effects and organoiron intermediates that enable effective alkyl-alkyl couplings. The current study addresses this longstanding limitation using a combination of Fe Mössbauer spectroscopy, SC-XRD (single-crystal X-ray diffraction) and reactivity studies of alkyl-alkyl coupling with iron-Xantphos to define the in situ formed iron-Xantphos intermediates in catalysis.

Caught in the Act of Substitution: Interadsorbate Effects on an Atomically Precise Fe/Co/Se Nanocluster.

Directing groups guide substitution patterns in organic synthetic schemes, but little is known about pathways to control reactivity patterns, such as regioselectivity, in complex inorganic systems such as bioinorganic cofactors or extended surfaces. Interadsorbate effects are known to encode surface reactivity patterns in inorganic materials, modulating the location and binding strength of ligands. However, owing to limited experimental resolution into complex inorganic structures, there is little opportunity to resolve these effects on the atomic scale.

Mechanistic investigations of the Fe(ii) mediated synthesis of squaraines.

The scission and homologation of CO is a fundamental process in the Fischer-Tropsch reaction. However, given the heterogeneous nature of the catalyst and forcing reaction conditions, it is difficult to determine the intermediates of this reaction. Here we report detailed mechanistic insight into the scission/homologation of CO by two-coordinate iron terphenyl complexes.

Unusual S=1 Four-Coordinate Fe(IV) Complexes Supported by Bisamide Ligands: Syntheses, Characterization, and Electronic Structures.

The catalytic relevance of Fe(IV) species in non-heme iron catalysis has motivated synthetic advances in well-defined five- and six-coordinate Fe(IV) complexes for a better understanding of their fundamental electronic structures and reactivities. Herein, we report the syntheses of FeDipp and FeMes, a pair of unusual four-coordinate non-heme formally Fe(IV) complexes with S=1 ground states supported by strongly donating bisamide ligands. By combining spectroscopic characterization and computational modeling, we found that small variations in ligand aryl substituents resulted in substantial changes in both structures and bonding.

Ni(2,2':6',2''-terpyridine): a high-spin octahedral formal Ni(0) complex.

We have synthesised and characterised the complex Ni(tpy) (tpy = 2,2':6',2''-terpyridine). This formally Ni(0) complex is paramagnetic both in the solid state and in solution ( = 2). The crystal structure shows an octahedral geometry, with molecules arranged in independent dimers involving π-stacking between pairs of complexes.

Iron-catalyzed stereoselective C-H alkylation for simultaneous construction of C-N axial and C-central chirality.

The assembly of chiral molecules with multiple stereogenic elements is challenging, and, despite of indisputable advances, largely limited to toxic, cost-intensive and precious metal catalysts. In sharp contrast, we herein disclose a versatile C-H alkylation using a non-toxic, low-cost iron catalyst for the synthesis of substituted indoles with two chiral elements. The key for achieving excellent diastereo- and enantioselectivity was substitution on a chiral N-heterocyclic carbene ligand providing steric hindrance and extra represented by noncovalent interaction for the concomitant generation of C-N axial chirality and C-stereogenic center.

Divergent Fe-Mediated C-H Activation Paths Driven by Alkali Cations.

The association of the ferrous complex FeCl(dmpe) () with alkali bases M(hmds) (M = Li, Na, K) proves to be an efficient platform for the activation of Ar-H bonds. Two mechanisms can be observed, leading to either Ar-Fe species by deprotonative ferration or hydrido species Ar-Fe-H by oxidative addition of transient Fe(dmpe) generated by reduction of . Importantly, the nature of the alkali cation in M(hmds) has a strong influence on the preferred path.

Mechanistic manifold in a hemoprotein-catalyzed cyclopropanation reaction with diazoketone.

Hemoproteins have recently emerged as promising biocatalysts for new-to-nature carbene transfer reactions. However, mechanistic understanding of the interplay between productive and unproductive pathways in these processes is limited. Using spectroscopic, structural, and computational methods, we investigate the mechanism of a myoglobin-catalyzed cyclopropanation reaction with diazoketones.

Palladium and Iron Cocatalyzed Aerobic Alkene Aminoboration.

Aminoboration of simple alkenes with nitrogen nucleophiles remains an unsolved problem in synthetic chemistry; this transformation can be catalyzed by palladium aminopalladation followed by transmetalation with a diboron reagent. However, this catalytic process faces inherent challenges with instability of the alkylpalladium(II) intermediate toward β-hydride elimination. Herein, we report a palladium/iron cocatalyzed aminoboration, which enables this transformation.

Mechanistic Studies of Iron-PyBOX-Catalyzed Olefin Amino-Oxygenation with Functionalized Hydroxylamines.

Iron-catalyzed amino-oxygenation of olefins often uses discrete ligands to increase reactivity and broaden substrate scope. This work is focused on examining ligand effects on reactivity and in situ iron speciation in a system which utilizes a bisoxazoline ligand. Freeze-trapped Fe Mössbauer and EPR spectroscopies as well as SC-XRD experiments were utilized to isolate and identify the species formed during the catalytic reaction of amino-oxygenation of olefins with functionalized hydroxylamines, as well as in the precatalytic mixture of iron salt and ligand.

Insight into Radical Initiation, Solvent Effects, and Biphenyl Production in Iron-Bisphosphine Cross-Couplings.

Iron-bisphosphines have attracted broad interest as highly effective and versatile catalytic systems for two- and three-component cross-coupling strategies. While recent mechanistic studies have defined the role of organoiron(II)-bisphosphine species as key intermediates for selective cross-coupled product formation in these systems, mechanistic features that are essential for catalytic performance remain undefined. Specifically, key questions include the following: what is the generality of iron(II) intermediates for radical initiation in cross-couplings? What factors control reactivity toward homocoupled biaryl side-products in these systems? Finally, what are the solvent effects in these reactions that enable high catalytic performance? Herein, we address these key questions by examining the mechanism of enantioselective coupling between α-chloro- and α-bromoalkanoates and aryl Grignard reagents catalyzed by chiral bisphosphine-iron complexes.

The molecular-level effect of alkoxide additives in iron-catalyzed Kumada cross-coupling with simple ferric salts.

The molecular-level role of alkoxide salts, used as alternative additive to -methylpyrrolidone in iron-catalyzed alkyl-alkenyl/aryl cross-coupling reactions, is investigated. Detailed spectroscopic studies reveal that alkoxides promote the formation of homoleptic organoferrates such as [FeMe], providing an alternative to toxic NMP to access these reactive intermediates.

Air-Stable Iron-Based Precatalysts for Suzuki-Miyaura Cross-Coupling Reactions between Alkyl Halides and Aryl Boronic Esters.

The development of an air-stable iron(III)-based precatalyst for the Suzuki-Miyaura cross-coupling reaction of alkyl halides and unactivated aryl boronic esters is reported. Despite benefits to cost and toxicity, the proclivity of iron(II)-based complexes to undergo deactivation oxidation or hydrolysis is a limiting factor for their widespread use in cross-coupling reactions compared to palladium-based or nickel-based complexes. The new octahedral iron(III) complex demonstrates long-term stability on the benchtop as assessed by a combination of H NMR spectroscopy, Mössbauer spectroscopy, and its sustained catalytic activity after exposure to air.

Homoleptic Uranium-Bis(acyl)phosphide Complexes.

The first uranium bis(acyl)phosphide (BAP) complexes were synthesized from the reaction between sodium bis(mesitoyl)phosphide () or sodium bis(2,4,6-triisopropylbenzoyl)phosphide () and UI(1,4-dioxane). Thermally stable, homoleptic BAP complexes were characterized by single-crystal X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy, when appropriate, for the elucidation of the electronic structure and bonding of these complexes. EPR spectroscopy revealed that the BAP ligands on the uranium center retain a significant amount of electron density.

Additive and Counterion Effects in Iron-Catalyzed Reactions Relevant to C-C Bond Formation.

The use of iron catalysts in carbon-carbon bond forming reactions is of interest as an alternative to precious metal catalysts, offering reduced cost, lower toxicity, and different reactivity. While well-defined ligands such as -heterocyclic carbenes (NHCs) and phosphines can be highly effective in these reactions, additional additives such as -methylpyrrolidone (NMP), ','-tetramethylethylenediamine (TMEDA), and iron salts that alter speciation can also be employed to achieve high product yields. However, in contrast to well-defined iron ligands, the roles of these additives are often ambiguous, and molecular-level insights into how they achieve effective catalysis are not well-defined.

Anion-induced disproportionation of Th(III) complexes to form Th(II) and Th(IV) products.

A new synthesis of Th(II) complexes has been identified involving addition of simple MX salts (M = Li, Na, K; X = H, Cl, Me, N) to Cp''Th [Cp'' = [CH(SiMe)] in the presence of 18-crown-6 or 2.2.2-cryptand, forming [M(chelate)][Cp''Th] and Cp''ThX.

High viral loads: what drives fatal cases of COVID-19 in vaccinees? - an autopsy study.

The rate of SARS-CoV-2 infections in vaccinees has become a relevant serious issue. This study aimed to determine the causes of death, histological organ alteration, and viral spread in relation to demographic, clinical-pathological, viral variants, and vaccine types for deceased individuals with proven SARS-CoV-2 infection after vaccination who died between January and November 2021. Twenty-nine consecutively collected cases were analyzed and compared to 141 nonvaccinated control cases.

Side-on coordination of diphosphorus to a mononuclear iron center.

The diagonal relationship in the periodic table between phosphorus and carbon has set an expectation that the triple-bonded diatomic diphosphorus molecule (P) should more closely mimic the attributes of acetylene (HC≡CH) rather than its group 15 congener dinitrogen (N). Although acetylene has well-documented coordination chemistry with mononuclear transition metals, coordination complexes that feature P bound to a single metal center have remained elusive. We report the isolation and x-ray crystallographic characterization of a mononuclear iron complex featuring P coordination in a side-on, η-binding mode.

A TMEDA-Iron Adduct Reaction Manifold in Iron-Catalyzed C(sp )-C(sp ) Cross-Coupling Reactions.

Herein, we expand the current molecular-level understanding of one of the most important and effective additives in iron-catalyzed cross-coupling reactions, N,N,N',N'-tetramethylethylenediamine (TMEDA). Focusing on relevant phenyl and ethyl Grignard reagents and slow nucleophile addition protocols commonly used in effective catalytic systems, TMEDA-iron(II)-aryl intermediates are identified via in situ spectroscopy, X-ray crystallography, and detailed reaction studies to be a part of an iron(II)/(III)/(I) reaction cycle where radical recombination with FePhBr(TMEDA) (2 ) results in selective product formation in high yield. These results differ from prior studies with mesityl Grignard reagent, where poor product selectivity and low catalytic performance can be attributed to homoleptic iron-ate species.

Creation of an unexpected plane of enhanced covalency in cerium(III) and berkelium(III) terpyridyl complexes.

Controlling the properties of heavy element complexes, such as those containing berkelium, is challenging because relativistic effects, spin-orbit and ligand-field splitting, and complex metal-ligand bonding, all dictate the final electronic states of the molecules. While the first two of these are currently beyond experimental control, covalent M‒L interactions could theoretically be boosted through the employment of chelators with large polarizabilities that substantially shift the electron density in the molecules. This theory is tested by ligating Bk with 4'-(4-nitrophenyl)-2,2':6',2"-terpyridine (terpy*), a ligand with a large dipole.

Intermediates and mechanism in iron-catalyzed C-H methylation with trimethylaluminum.

A mechanistic study is performed on the reaction method for iron-catalyzed C-H methylation with AlMe reagent, previously proposed to involve cyclometalated iron(III) intermediates and an iron(III)/(I) reaction cycle. Detailed spectroscopic studies (Fe Mössbauer, EPR) during catalysis and in stoichiometric reactions identify iron(II) complexes, including cyclometalated iron(II) intermediates, as the major iron species formed under catalytic reaction conditions. Reaction studies identify a cyclometalated iron(II)-methyl species as the key intermediate leading to C-H methylated product upon reaction with oxidant, consistent with a previously proposed iron(II)/iron(III)/iron(I) reaction manifold for C-H arylation.

General method for iron-catalyzed multicomponent radical cascades-cross-couplings.

Transition metal–catalyzed cross-coupling reactions are some of the most widely used methods in chemical synthesis. However, despite notable advantages of iron (Fe) as a potentially cheaper, more abundant, and less toxic transition metal catalyst, its practical application in multicomponent cross-couplings remains largely unsuccessful. We demonstrate 1,2-bis(dicyclohexylphosphino)ethane Fe–catalyzed coupling of α-boryl radicals (generated from selective radical addition to vinyl boronates) with Grignard reagents.