Alkyl Coordination in -(ONO) Supported Uranium(IV) Complexes.

A series of U(IV) complexes bearing alkyl and chloride ligands in the configuration was synthesized and characterized. Starting with the diastereopure U(IV) -dichloride complex -( ONO)UCl(dtbpy) (, ONO = 2,6-bis((di--butylphosphino)methanolato)pyridine), four distinct alkyl groups were employed to prepare ( ONO)U(R)Cl(dtbpy), where R = (trimethylsilyl)methyl (neosilyl), , R = 2,2-dimethyl propyl (neopentyl), , and R = 2-methyl-2-phenyl propyl (neophyl), . Alkylation occurs with specificity but generates a predominant species and a minor species corresponding to / regioisomers relative to the P groups of the ligand.

Determining the Effects of Zero-Field Splitting and Magnetic Exchange in Dimeric Europium(II) Complexes.

Related BAP [BAP = bis(acyl)phosphide] and Acac (Acac = β-diketonate) molecules perform as robust supports for both lanthanide and actinide metals. Here, a molecular bimetallic Eu complex was successfully targeted and isolated by employing sodium bis(mesitoyl)phosphide [Na(BAP)] in a salt metathesis with EuI, producing (eto = metal-coordinated diethyl ether). The corresponding Acac-Eu complex was targeted using Acac (1,3-dimesityl-1,3-propanedione), generating .

Oxidative Dissolution of Lanthanide Metals Ce and Ho in Molten GaCl.

Gallium trichloride (GaCl) was used as a solvent for the oxidative dissolution of the lanthanide (Ln) metals cerium (Ce) and holmium (Ho). Reactions were performed at temperatures above 100 °C in sealed vessels to maintain the liquid phase for GaCl during the oxidizing reactions. The best results were obtained from reactions using 8 equiv of GaCl to metal where the inorganic complexes [Ga][Ln(GaCl)] [Ln = Ce (), Ho ()] could be isolated.

Deferasirox Derivatives: Ligands for the Lanthanide Series.

Deferasirox is an FDA-approved iron chelator used in the treatment of iron toxicity. In this work, we report the use of several deferasirox derivatives as lanthanide chelators. Solid-state structural studies of three representative trivalent lanthanide cations, La(III), Eu(III), and Lu(III), revealed the formation of 2:2 complexes in the solid state.

Chlorination of Pu and U Metal Using GaCl.

The oxidative chlorination of the plutonium metal was achieved through a reaction with gallium(III) chloride (GaCl). In DME (DME = 1,2-dimethoxyethane) as the solvent, substoichiometric (2.8 equiv) amounts of GaCl were added, which consumed roughly 60% of the plutonium metal over the course of 10 days.

Magnetism Studies of Bis(acyl)phosphide-Supported Eu and Eu Complexes.

A series of bis(acyl)phosphide-supported Eu complexes were synthesized (bis(acyl)phosphide = BAP). In this study, BAP ligands proved to be excellent ligands for the synthesis of both Eu and Eu molecular complexes. Sodium bis(mesitoyl)phosphide () and sodium bis(2,4,6-triisopropylbenzoyl)phosphide () were employed as ligand precursors for the synthesis of the Eu complexes Eu(bis(mesitoyl)phosphide)(thf) () and Eu(bis(2,4,6-triisopropylbenzoyl)phosphide) (), as well as the Eu complex, Eu(bis(2,4,6-triisopropylbenzoyl)phosphide)(dme) () (thf = tetrahydrofuran, dme = 1,2-dimethoxyethane).

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.

An Allyl Uranium(IV) Sandwich Complex: Are Ï• Bonding Interactions Possible?

A method to explore head-to-head ϕ back-bonding from uranium f-orbitals into allyl π* orbitals has been pursued. Anionic allyl groups were coordinated to uranium with tethered anilide ligands, then the products were investigated by using NMR spectroscopy, single-crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N-((dimethyl)prop-2-enylsilyl)-2,6-diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, thereby highlighting the stability and versatility of the silylanilide motif.

Experimental and computational studies of the mechanism of iron-catalysed C-H activation/functionalisation with allyl electrophiles.

Synthetic methods that utilise iron to facilitate C-H bond activation to yield new C-C and C-heteroatom bonds continue to attract significant interest. However, the development of these systems is still hampered by a limited molecular-level understanding of the key iron intermediates and reaction pathways that enable selective product formation. While recent studies have established the mechanism for iron-catalysed C-H arylation from aryl-nucleophiles, the underlying mechanistic pathway of iron-catalysed C-H activation/functionalisation systems which utilise electrophiles to establish C-C and C-heteroatom bonds has not been determined.

Identification and Reactivity of Cyclometalated Iron(II) Intermediates in Triazole-Directed Iron-Catalyzed C-H Activation.

While iron-catalyzed C-H activation offers an attractive reaction methodology for organic transformations, the lack of molecular-level insight into the in situ formed and reactive iron species impedes continued reaction development. Herein, freeze-trapped Fe Mössbauer spectroscopy and single-crystal X-ray crystallography combined with reactivity studies are employed to define the key cyclometalated iron species active in triazole-assisted iron-catalyzed C-H activation. These studies provide the first direct experimental definition of an activated intermediate, which has been identified as the low-spin iron(II) complex [(sub-A)(dppbz)(THF)Fe](μ-MgX), where sub-A is a deprotonated benzamide substrate.

Crystal structure of bromido-penta-kis-(tetra-hydro-furan-κ)magnesium bis-[1,2-bis-(di-phenyl-phosphan-yl)benzene-κ ,']cobaltate(-1) tetra-hydro-furan disolvate.

Structural characterization of the ionic title complex, [MgBr(THF)][Co(dpbz)]·2THF [THF is tetra-hydro-furan, CHO; dpbz is 1,2-bis-(di-phenyl-phosphan-yl)benzene, CHP], revealed a well-separated cation and anion co-crystallized with two THF solvent mol-ecules that inter-act with the cation weak C-H⋯O contacts. The geometry about the cobalt center is pseudo-tetra-hedral, as is expected for a metal center, only deviating from an ideal tetra-hedral geometry because of the restrictive bite angles of the bidentate phosphane ligands. Three THF ligands of the cation and one co-crystallized THF solvent mol-ecule are each disordered over two orientations.

The Effect of β-Hydrogen Atoms on Iron Speciation in Cross-Couplings with Simple Iron Salts and Alkyl Grignard Reagents.

The effects of β-hydrogen-containing alkyl Grignard reagents in simple ferric salt cross-couplings have been elucidated. The reaction of FeCl with EtMgBr in THF leads to the formation of the cluster species [Fe Et ] , a rare example of a structurally characterized metal complex with bridging ethyl ligands. Analogous reactions in the presence of NMP, a key additive for effective cross-coupling with simple ferric salts and β-hydrogen-containing alkyl nucleophiles, result in the formation of [FeEt ] .

Development and Evolution of Mechanistic Understanding in Iron-Catalyzed Cross-Coupling.

Since the pioneering work of Kochi in the 1970s, iron has attracted great interest for cross-coupling catalysis due to its low cost and toxicity as well as its potential for novel reactivity compared to analogous reactions with precious metals like palladium. Today there are numerous iron-based cross-coupling methodologies available, including challenging alkyl-alkyl and enantioselective methods. Furthermore, cross-couplings with simple ferric salts and additives like NMP and TMEDA ( N-methylpyrrolidone and tetramethylethylenediamine) continue to attract interest in pharmaceutical applications.

Multinuclear iron-phenyl species in reactions of simple iron salts with PhMgBr: identification of Fe(μ-Ph)(THF) as a key reactive species for cross-coupling catalysis.

The first direct syntheses, structural characterizations, and reactivity studies of iron-phenyl species formed upon reaction of Fe(acac) and PhMgBr in THF are presented. Reaction of Fe(acac) with 4 equiv. PhMgBr in THF leads to the formation of [FePh(μ-Ph)] at -80 °C, which can be stabilized through the addition of -methylpyrrolidone.

Crystal structures of two new six-coordinate iron(III) complexes with 1,2-bis(diphenyl-phosphane) ligands.

Structural characterization of the ionic complexes [FeCl(CHP)][FeCl]·0.59CHCl or [(dppen)FeCl][FeCl]·0.59CHCl (dppen = -1,2-bis-(di-phenyl-phosphane)ethyl-ene, PCH) and [FeCl(CHP)][FeCl]·CHCl or [(dpbz)FeCl][FeCl]·CHCl (dpbz = 1,2-bis-(di-phenyl-phosphane)benzene, PCH) demonstrates coordination of two bidentate phosphane ligands (bis-phosphanes) to a single iron(III) center, resulting in six-coordinate cationic complexes that are balanced in charge by tetra-chlorido-ferrate(III) monoanions.

The N-Methylpyrrolidone (NMP) Effect in Iron-Catalyzed Cross-Coupling with Simple Ferric Salts and MeMgBr.

The use of N-methylpyrrolidone (NMP) as a co-solvent in ferric salt catalyzed cross-coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross-coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP) ][FeMe ] (1), which forms as the major iron species in situ in reactions of Fe(acac) and MeMgBr under catalytically relevant conditions where NMP is employed as a co-solvent.

A Physical-Inorganic Approach for the Elucidation of Active Iron Species and Mechanism in Iron-Catalyzed Cross-Coupling.

Detailed studies of iron speciation and mechanism in iron-catalyzed cross-coupling reactions are critical for providing the necessary fundamental insight to drive new reaction development. However, such insight is challenging to obtain due to the prevalence of mixtures of unstable, paramagnetic organoiron species that can form in this chemistry. A physical-inorganic research approach combining freeze-trapped inorganic spectroscopic studies, organometallic synthesis and GC/kinetic studies provides a powerful method for studying such systems.

Polyoxovanadate-Alkoxide Clusters as a Redox Reservoir for Iron.

Inspired by the multielectron redox chemistry achieved using conventional organic-based redox-active ligands, we have characterized a series of iron-functionalized polyoxovanadate-alkoxide clusters in which the metal oxide scaffold functions as a three-dimensional, electron-deficient metalloligand. Four heterometallic clusters were prepared through sequential reduction, demonstrating that the metal oxide scaffold is capable of storing up to four electrons. These reduced products were characterized by cyclic voltammetry, IR, electronic absorption, and H NMR spectroscopies.

Facile hydrogen atom transfer to iron(iii) imido radical complexes supported by a dianionic pentadentate ligand.

A dianionic tetrapodal pentadentate diborate ligand is introduced. This ligand forms a high spin neutral iron(ii) complex that reacts with a variety of organoazides to yield transient Fe(iii) imido radicals that are extremely potent hydrogen atom abstractors. The nature of these species is supported by full characterization of the Fe(iii) amido products, kinetic studies, density functional computations and Mössbauer spectroscopy on the -CH-- Bu substituted derivative.

Manipulating Magneto-Optic Properties of a Chiral Polymer by Doping with Stable Organic Biradicals.

We report the first example of tuning the large magneto-optic activity of a chiral polymer by addition of stable organic biradicals. The spectral dispersion of Verdet constant, which quantifies magneto-optic response, differs substantially between the base polymer and the nanocomposite. We employed a microscopic model, supported by atomistic calculations, to rationalize the behavior of this nanocomposite system.