Coordination-induced axial chirality controls the metal-centred configuration in a stereogenic-at-iron catalyst.

A new approach is introduced to control the metal-centred configuration of stereogenic-at-iron catalysts by utilizing axial ligand chirality, which becomes locked upon metal coordination. This strategy is applied to an iron catalyst containing two chelating -(2-pyridyl)-substituted triazol-5-ylidene mesoionic carbenes (MICs) resulting in a helical topology with a stereogenic iron centre.

Synthesis of Iron(IV) Alkynylide Complexes and Their Reactivity to Form 1,3-Diynes.

The isolation of thermally unstable and highly reactive organoiron(IV) complexes is a challenge for synthetic chemists. In particular, the number of examples where the C-based ligand is not part of the chelating ligand remains scarce. These compounds are of interest because they could pave the way to designing catalytic cycles of bond forming reactions proceeding via organoiron(IV) intermediates.

β-Tryptophans by Iron-Catalyzed Enantioselective Amination of 3-Indolepropionic Acids.

A straightforward and general strategy for the catalytic asymmetric synthesis of β-tryptophans by carboxylic-acid-directed intermolecular C-H amination has been developed. The iron-catalyzed C-H amination of 3-indolepropionic acids with BocNHOMs (Boc, -butyloxycarbonyl; OMs, methylsulfonate) in the presence of the base piperidine provides N-Boc-protected β-tryptophans in a single step with high enantiomeric excess (ee) of up to >99%. Mechanistic experiments and density functional theory calculations support a mechanism through carboxylate-directed iron-mediated C(sp)-H nitrene insertion.

Stereogenic-at-iron mesoionic carbene complex for enantioselective C-H amidation.

Electronically tuned -symmetric stereogenic-at-iron complexes, featuring strongly σ-donating 1,2,3-triazolin-5-ylidene mesoionic carbene (MIC) ligands, exhibit enhanced catalytic efficiency compared to conventional imidazol-2-ylidene analogs, as demonstrated in nitrene-mediated ring-closing C(sp)-H amidation reactions. Furthermore, a chiral pinene-derived pyridyl triazole ligand enables a highly diastereoselective synthesis of a non-racemic chiral iron catalyst, thereby controlling the absolute configuration at the metal center, as confirmed by NMR and X-ray crystallography. This pinene-modified stereogenic-at-iron MIC complex demonstrates high catalytic activity and a respectable asymmetric induction in the ring-closing C(sp)-H amination of -benzoyloxyurea, yielding 2-imidazolidinones with enantiomeric ratios of up to 92 : 8.

Multinuclear Beryllium Chloro Carboxylates.

Reaction of 1 equiv of BeCl with mesityl (Mes) or -tolyl (-Tol) carboxylic acid in benzene gives hexanuclear heterocyles [BeCl(MesCO)] and [BeCl(-TolCO)], respectively. Small amounts of the oxocarboxylates [BeO(MesCO)] and [BeO(-TolCO)] are also formed. If chloroform is used as the solvent, a mixture of these complexes together with the unprecedented tertranuclear cage compounds [BeCl(MesCO)] and [BeCl(-TolCO)] is obtained.

Multinuclear beryllium amide and imide complexes: structure, properties and bonding.

The beryllium amide and imide complexes [Be(HNMes)], [(py)Be(HNMes)], [Be(HNDipp)], [Be(NPh)(μ-HNDipp)] and [Be(NCPh)] have been prepared and characterised with NMR and IR spectroscopy as well as single crystal X-ray diffraction. Analysis of the localised molecular orbitals (LMOs) and intrinsic atomic orbital (IAO) atomic charges in the framework of the intrinsic bond orbital (IBO) localization method revealed a covalent bonding network consisting of 2-electron-2-centre and 2-electron-3-centre σ bonds, in which one electron pair of the anionic N-donor ligands is involved. The electron deficiency at the beryllium atoms is partially compensated through additional electron donation from the lone pair at the nitrogen atoms.

Mono-Ortho-Beryllated Carbodiphosphoranes: Synthesis, Structure, Bonding and Reactivity.

The reaction of organoberyllium compounds with hexaphenylcarbodiphosphorane yields mono-ortho-beryllated complexes, which feature a double dative Be=C bond. The bonding situation in these compounds together with a simple carbodiphosphorane and an N-heterocyclic carbene adduct was analysed with energy decomposition analysis in combination with natural orbital for chemical valence as well as with quantum theory of atoms-in-molecules. Furthermore, the driving forces accountable for mono-ortho-beryllation were elucidated along with the reactivity of the Be=C bond.

Synthesis and Derivatives of Beryllium Triflate.

Various pathways for the synthesis of beryllium triflate were investigated. The reaction of triflic acid or trimethylsilyl triflate with beryllium metal in liquid ammonia led to the formation of mono-, di-, and tetra-nuclear beryllium ammine complexes. Utilization of SMe as a solvent gave homoleptic Be(OTf).

Nitrene-Mediated Enantioselective Intramolecular Olefin Oxyamination to Access Chiral γ-Aminomethyl-γ-Lactones.

Attaching a nitrene precursor to an intramolecular nucleophile allows for a catalytic asymmetric intramolecular oxyamination of alkenes in which the nucleophile adds in an endocyclic position and the amine in an exocyclic fashion. Using chiral-at-ruthenium catalysts, chiral γ-aminomethyl-γ-lactones containing a quaternary carbon in γ-position are provided in high yields (up to 99 %) and with excellent enantioselectivities (up to 99 % ee). DFT calculations support the possibility of both a singlet (concerted oxyamination of the alkene) and triplet pathway (stepwise oxyamination) for the formation of the predominant stereoisomer.

Experimental and Computational Studies on Cobalt(I)-Catalyzed Regioselective Allylic Alkylation Reactions.

Here, we report the development of cobalt(I)-catalyzed regioselective allylic alkylation reactions of tertiary allyl carbonates with 1,3-dicarbonyl compounds. A family of well-defined tetrahedral cobalt(I) complexes bearing commercially available bidentate bis(phosphine) ligands [(P,P)Co(PPh )Cl] are synthesized and explored as catalysts in allylic alkylation reactions. The catalyst [(dppp)Co(PPh )Cl] (dppp=1,3-Bis(diphenylphosphino)propane) enables the alkylation of a large variety of tertiary allyl carbonates with high yields and excellent regioselectivity for the branched product.

Gauging ambiphilicity of pseudo-halides beryllium-trispyrazolylborato compounds.

The ambiphilicity of pseudo-halides has been the object of extensive debate. Herein, we use a series of trispyrazolylborato beryllium pseudo-halido complexes [TpBe(X')] with X' = CN, N, NCO and NCS to explore the origins of the preferred isomers. Thus, we have synthesised and characterised through NMR and IR spectroscopy as well as single crystal X-ray diffraction these complexes.

A Preference for Heterolepticity - Schlenk Type Equilibria in Organometallic Beryllium Systems.

The reaction of homoleptic beryllium halide with diphenyl beryllium complexes leads to the clean formation of heteroleptic beryllium Grignard compounds [(L) BePhX] (X=Cl, Br, I; L=C-, N-, O-donor ligand). The influence of ligands and solvent on these compounds, their formation and exchange equilibria in solution were investigated, together with the factors determining the complex constitution.

Trading Symmetry for Stereoinduction in Tetradentate, non-C -Symmetric Fe(II)-Complexes for Asymmetric Catalysis.

A series of stereogenic-at-metal iron complexes comprising a non-C -symmetric chiral topology is introduced and applied to asymmetric 3d-transition metal catalysis. The chiral iron(II) complexes are built from chiral tetradentate N4-ligands containing a proline-derived amino pyrrolidinyl backbone which controls the relative (cis-α coordination) and absolute metal-centered configuration (Λ vs. Δ).

Ligand exchange at tetra-coordinated beryllium centres.

Mono and dinuclear phosphine complexes of beryllium halides [(PMe)BeX], [(PMe)BeX] and [(PCy)BeX] (X = Cl, Br, I) were synthesised and characterised NMR and IR spectroscopy as well as single crystal X-ray diffraction experiments. Dissociation and ligand exchange processes at these complexes were investigated through variable temperature NMR experiments in combination with line shape analysis and complemented by quantum chemical calculations. The PMe dissociation energy is smallest in [(PMe)BeCl], while PMe exchange is similar in energy in all mononuclear [(PMe)BeX] complexes and follows an interchange mechanism.

Exchange Interactions and Magnetic Properties of a Molecular Mn -Ring Complex.

[Mn O(OAc) (HOAc)]  ⋅ x AcOH (x=6-9) represents a rare example of a compound containing molecular Mn -rings. These are formed by Mn (μ -O) subunits in which the high-spin Mn(III) centers are bridged by three pairs of acetate anions (AcO ). An AcOH molecule coordinates to one of the Mn atoms leading to [Mn (μ -O)(μ -OAc) (AcOH)]-units, designated in short as Mn -units, that are interconnected by acetate anions via the other two Mn atoms to form Mn -rings.

Improving the Configurational Stability of Chiral-at-Iron Catalysts Containing Two -(2-Pyridyl)-Substituted N-Heterocyclic Carbene Ligands.

Recently, we introduced the first example of chiral-at-iron catalysts in which two achiral -(2-pyridyl)-substituted N-heterocyclic carbene (NHC) ligands in addition to two labile acetonitriles are coordinated around a central iron, to generate a stereogenic metal center [Hong Y.Chiral-at-Iron Catalyst: Expanding the Chemical Space for Asymmetric Earth-Abundant Metal Catalysis. J.

Nitrene-Mediated C-H Oxygenation: Catalytic Enantioselective Formation of Five-Membered Cyclic Organic Carbonates.

The synthesis of non-racemic 5-membered cyclic carbonates from abundant alcohols is reported. Conversion of the alcohol into an azanyl carbonate is followed by a chiral-at-ruthenium catalyzed cyclization to provide chiral cyclic carbonates in yields of up to 95 % and with up to 99 % ee. This new synthetic method is proposed to proceed through a nitrene-mediated intramolecular C(sp )-H oxygenation which includes an unusual 1,7-hydrogen atom transfer within a ruthenium nitrene intermediate.

Surprises in the Solvent-Induced Self-Ionization in the Uranium Tetrahalide UX (X = Cl, Br, I)/Ethyl Acetate System.

The reaction of the uranium(IV) halides UCl, UBr, or UI with ethyl acetate (EtOAc) leads to the formation of the complexes [UX(EtOAc)][UX(EtOAc)] (X = Cl, Br) or [UI(EtOAc)]. Thus, both UCl and UBr show self-ionization in ethyl acetate to a distorted pentagonal bipyramidal [UX(EtOAc)] cation and a distorted octahedral [UX(EtOAc)] anion. Surprisingly, the chloride and bromide compounds are not isotypic.

Reactivity of Diphenylberyllium as a Brønsted Base and Its Synthetic Application.

Diphenylberyllium [Be Ph ] is shown here to react cleanly as a Brønsted base with a vast variety of protic compounds. Through the addition of the simple molecules tBuOH, HNPh and HPPh , as well as the more complex 1,3-bis-(2,6-diisopropylphenyl)imidazolinium chloride, one or two phenyl groups in diphenylberyllium were protonated. As a result, the long-postulated structures of [Be (OtBu) ] and [Be(μ-NPh )Ph] have finally been verified and shown to be static in solution.

Electrochemical Enantioselective Nucleophilic α-C(sp)-H Alkenylation of 2-Acyl Imidazoles.

Merging electrochemistry with asymmetric catalysis promises to provide an environmentally friendly and efficient strategy for the construction of nonracemic chiral molecules. However, in practice, significant challenges arise from the instability or incompatibility of the chiral catalysts under the electrochemical conditions at the interface of electrode and solution. Herein, we report a catalytic asymmetric indirect electrolysis employing the combination of a redox mediator and a chiral-at-rhodium Lewis acid, which achieves a previously elusive enantioselective nucleophilic αC(sp)H alkenylation of ketones.

Synthesis of Fe and Fe Cyanide Complexes Using Hypervalent Iodine Reagents as Cyano-Transfer One-Electron Oxidants.

We disclose a new reactivity mode for electrophilic cyano λ -iodanes as group transfer one-electron oxidants to synthesize Fe and Fe cyanide complexes. The inherent thermal instability of high-valent Fe compounds without π-donor ligands (such as oxido (O ), imido (RN ) or nitrido (N )) makes their isolation and structural characterization a very challenging task. We report the synthesis of an Fe cyanide complex [(N N')FeCN] (4) by two consecutive single electron transfer (SET) processes from Fe precursor [(N N')FeLi(THF)] (1) with cyanobenziodoxolone (CBX).

Preussochromone Puzzle: Structural Revision of Preussochromones E and F by Total Synthesis.

A stereoselective synthesis of the proposed and actual structures of the natural products preussochromones E and F is reported. The key step is a ring-closing metathesis to close the five-membered ring and install the trans configuration of the annulated five-six ring system. The analysis of the NMR couplings of the isolated natural product with the synthesized compound revealed its real structure with a cis annulation, which could also be synthesized using an intramolecular aldol reaction of a -tricarbonyl compound.

π Back-Donation from a Beryllium Dibromide Fragment at the Expense of Its σ Strength.

It is common knowledge that metal-to-ligand π back-donation requires filled atomic orbitals at the metal center. However, we show through a combined experimental and theoretical approach that Be(II)→N-heterocyclic carbene (NHC) π back-donation is present in the two carbene adducts [(iPr)BeBr] () and [(iPr)BeBr] () (iPr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). These complexes were characterized with NMR, IR, and Raman spectroscopy as well as with single-crystal X-ray diffractometry.

Regioselective Fluorination of Acenes: Tailoring of Molecular Electronic Levels and Solid-State Properties.

Optoelectronic properties of molecular solids are important for organic electronic devices and are largely determined by the adopted molecular packing motifs. In this study, we analyzed such structure-property relationships for the partially regioselective fluorinated tetracenes 1,2,12-trifluorotetracene, 1,2,10,12-tetrafluorotetracene and 1,2,9,10,11-pentafluorotetracene that were further compared with tetracene and perfluoro-tetracene. Quantum chemical DFT calculations in combination with optical absorption spectroscopy data show that the frontier orbital energies are lowered with the degree of fluorination, while their optical gap is barely affected.

DFT-Guided Crystal Structure Redetermination and Lattice Dynamics of the Intermetallic Actinoid Compound UIr.

UIr has been discussed as a rare example of a noncentrosymmetric, ferromagnetic superconductor crystallizing in the acentric PdBi structure type (2, 16). Here we present a new structure model for UIr. By means of single-crystal and powder X-ray diffraction we find UIr to crystallize in the symmetric space group 2/, in line with previous calculations.