Formation, Structure and Reactivity of a Beryllium(0) Complex with Mgδ+-Beδ- Bond Polarization.

Attempts to create a novel Mg-Be bond by reaction of [(DIPePBDI*)MgNa]2 with Be[N(SiMe3)2]2 failed; DIPePBDI*=HC[(tBu)C=N(DIPeP)]2, DIPeP=2,6-Et2C-phenyl. Even at elevated temperatures, no conversion was observed. This is likely caused by strong steric shielding of the Be center. A similar reaction with the more open Cp*BeCl gave in quantitative yield (DIPePBDI*)MgBeCp* (1). The crystal structure shows a Mg-Be bond of 2.469(4) Å. Homolytic cleavage of the Mg-Be bond requires ΔH=69.6 kcal mol-1 (cf. CpBe-BeCp 69.0 kcal mol-1 and (DIPPBDI)Mg-Mg(DIPPBDI) 55.8 kcal mol-1). Natural-Population-Analysis (NPA) shows fragment charges: (DIPePBDI*)Mg +0.27/BeCp* -0.27. The very low NPA charge on Be (+0.62) compared to Mg (+1.21) and the strongly upfield 9Be NMR signal at -23.7 ppm are in line with considerable electron density on Be and the formal oxidation state assignment of MgII-Be0. Despite this Mgδ+-Beδ- polarity, 1 is extremely thermally stable and unreactive towards H2, CO, N2, cyclohexene and carbodiimide. It reacted with benzophenone, azobenzene, phenyl acetylene, CO2 and CS2. Reaction with 1-adamantyl azide led to reductive coupling and formation of an N6-chain. The azide reagent also inserted in the Cp*-Be bond. The inertness of 1 is likely due to bulky ligands protecting the Mg-Be unit.

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 SMe2 as a solvent gave homoleptic Be(OTf)2. Various beryllium triflate complexes with N- and O-donor ligands as well as the complex anions [Be(OTf)4]2- and [Be2(OTf)6]2- were synthesized to evaluate the reactivity and solution properties of beryllium triflate. This showed that OTf- is not a weakly coordinating anion for Be2+ cations and that it exhibits good bridging properties.

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.

Plasmachemical Syntheses of RuF6, RhF6, and PtF6.

Starting from the respective metal M, we have synthesized the hexafluorides MF6 of M = Ru, Rh, and Pt by the use of a laser-based heating system and a remote fluorine plasma source using a mixture of Ar and NF3 as the feed gas. The formation of the hexafluorides was confirmed by several different spectroscopic methods, including IR, Raman, UV/vis, and NMR spectroscopy. In addition, we present first experimental hints that RuF6 is more reactive than PtF6, because RuF6 is able to oxidize lower fluorides of platinum to PtF6.

Gauging ambiphilicity of pseudo-halides via 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-, N3-, 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 combination with quantum chemical calculations within the DFT framework enabled an in-depth understanding of the bonding modes and preferences of the investigated pseudo-halido ligands.

Reactivity of free N-heterocyclic carbenes in dichloromethane.

The reactivity of free 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (MeIPr) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IDipp) in dichloromethane was investigated. MeIPr reacts relatively slowly and selectively with the solvent under the formation of imidazolium salt [MeIPrH]Cl, which was characterised through NMR and IR spectroscopy as well as single crystal X-ray diffraction. Through deuterium labelling experiments the reaction rate was determined. In contrast IDipp reacts unselectively to various imidazolium salts. Due to the slow decomposition rates of MeIPr and IDipp in CH2Cl2, reactions of the free carbenes with BeBr2 to [(MeIPr)BeBr2], [(MeIPr)2BeBr2] and [(IDipp)BeBr2] can be performed.

Beryllium-Mediated Halide and Aryl Transfer onto Silicon.

The reactivity of hexamethylcyclotrisiloxane (D3 ) towards BeCl2 , BeBr2 , BeI2 and [Be3 Ph6 ]3 was investigated. While BeCl2 only showed unselective reactivity, BeBr2 , BeI2 and [Be3 Ph6 ] cleanly react to the trinuclear complexes [Be3 Br2 (OSiMe2 Br)4 ], [Be3 I2 (OSiMe2 I)4 ] and [Be3 Ph2 (OSiMe2 Ph)4 ]. These unprecedented bromide, iodide and phenyl transfer reactions from a group II metal onto silicon offer a versatile access to previously unknown diorgano bromo and iodo silanolates.

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)1-2 BePhX]1-2 (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.

Bismuth in Dynamic Covalent Chemistry: Access to a Bowl-Type Macrocycle and a Barrel-Type Heptanuclear Complex Cation.

Dynamic covalent chemistry (DCvC) is a powerful and widely applied tool in modern synthetic chemistry, which is based on the reversible cleavage and formation of covalent bonds. One of the inherent strengths of this approach is the perspective to reversibly generate in an operationally simple approach novel structural motifs that are difficult or impossible to access with more traditional methods and require multiple bond cleaving and bond forming steps. To date, these fundamentally important synthetic and conceptual challenges in the context of DCvC have predominantly been tackled by exploiting compounds of lighter p-block elements, even though heavier p-block elements show low bond dissociation energies and appear to be ideally suited for this approach. Here we show that a dinuclear organometallic bismuth compound, containing BiMe2 groups that are connected by a thioxanthene linker, readily undergoes selective and reversible cleavage of its Bi-C bonds upon exposure to external stimuli. The exploitation of DCvC in the field of organometallic heavy p-block chemistry grants access to unprecedented macrocyclic and barrel-type oligonuclear compounds.

Ligand exchange at tetra-coordinated beryllium centres.

Mono and dinuclear phosphine complexes of beryllium halides [(PMe3)2BeX2], [(PMe3)BeX2]2 and [(PCy3)BeX2]2 (X = Cl, Br, I) were synthesised and characterised via 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 PMe3 dissociation energy is smallest in [(PMe3)2BeCl2], while PMe3 exchange is similar in energy in all mononuclear [(PMe3)2BeX2] complexes and follows an interchange mechanism. While [(PMe3)BeX2]2 dissociates homolytically, [(PCy3)BeX2]2 cleaves one phosphine ligand. These distinctive dissociation processes account for the different chemical behaviour of these complexes.

Inducing Nucleophilic Reactivity at Beryllium with an Aluminyl Ligand.

The reactions of anionic aluminium or gallium nucleophiles {K[E(NON)]}2 (E = Al, 1; Ga, 2; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-ditert-butyl-9,9-dimethylxanthene) with beryllocene (BeCp2) led to the displacement of one cyclopentadienyl ligand at beryllium and the formation of compounds containing Be-Al or Be-Ga bonds (NON)EBeCp (E = Al, 3; Ga, 4). The Be-Al bond in the beryllium-aluminyl complex [2.310(4) Å] is much shorter than that found in the small number of previous examples [2.368(2) to 2.432(6) Å], and quantum chemical calculations suggest the existence of a non-nuclear attractor (NNA) for the Be-Al interaction. This represents the first example of a NNA for a heteroatomic interaction in an isolated molecular complex. As a result of this unusual electronic structure and the similarity in the Pauling electronegativities of beryllium and aluminium, the charge at the beryllium center (+1.39) in 3 is calculated to be less positive than that of the aluminium center (+1.88). This calculated charge distribution suggests the possibility for nucleophilic behavior at beryllium and correlates with the observed reactivity of the beryllium-aluminyl complex with N,N'-diisopropylcarbodiimide─the electrophilic carbon center of the carbodiimide undergoes nucleophilic attack by beryllium, thereby yielding a beryllium-diaminocarbene complex.

Bonding situations in tricoordinated beryllium phenyl complexes.

The bonding situation in the tricoordinated beryllium phenyl complexes [BePh3 ]- , [(pyridine)BePh2 ] and [(trimethylsilyl-N-heterocyclic imine)BePh2 ] is investigated experimentally and computationally. Comparison of the NMR spectroscopic properties of these complexes and of their structural parameters, which were determined by single crystal X-ray diffraction experiments, indicates the presence of π-interactions. Topology analysis of the electron density reveals elliptical electron density distributions at the bond critical points and the double bond character of the beryllium-element bonds is verified by energy decomposition analysis with the combination of natural orbital for chemical valence. The present beryllium-element bonds are highly polarized and the ligands around the central atom have a strong influence on the degree of π-delocalization. These results are compared to related triarylboranes.

Small compound - big colors: synthesis and structural investigation of brightly colored alkaline earth metal 1,3-dimethylviolurates.

A series of brightly colored alkaline earth metal 1,3-dimethylviolurates M(Me2Vio)2 have been prepared and fully characterized. The title compounds AE(Me2Vio)2·nH2O (AE = Mg, n = 6 (3); AE = Ca, n = 8 (4), AE = Sr, n = 6 (5); AE = Ba, n = 4 (6)) were obtained by neutralizing 1,3-dimethylvioluric acid monohydrate (=H(Me2Vio)·H2O; 2) with 0.5 equiv. of the corresponding metal dihydroxides AE(OH)2. The hair-like appearance of the Sr derivative 5 prevented the growth of single-crystals. This problem could be solved by crystallizing the crown ether derivative Sr(Me2Vio)2(18-crown-6) (5a). The isolated salts exhibit intense colors ranging from red to purple. Various attempts to prepare the beryllium derivative Be(Me2Vio)2 failed. Instead, work-up of the reaction mixtures provided pink crystals of a new modification of 2 formulated as [H3O][Me2Vio] (2b) as shown by an X-ray diffraction study. An unexpected oxidation reaction of the barium salt Ba(Me2Vio)2 led to formation of the novel mixed-anion salt Ba(Me2Vio)(Me2NO2Barb)·2H2O (8, Me2NO2Barb- = 1,3-dimethyl-5-nitrobarbiturate anion). Compound 8 could also be synthesized deliberately by treatment of Ba(OH)2 with a 1 : 1 mixture of 2 and 1,3-dimethyl-5-nitrobarbituric acid (7, =H(Me2NO2Barb)·H2O). All new compounds were fully characterized by their IR, Raman, NMR (1H, 13C{1H}) and UV-vis spectra as well as elemental analyses. Single-crystal X-ray diffraction studies revealed that the solid-state structures of compounds 3, 4, 5a and 6 are governed by the typical coordination behavior of the alkaline-earth metals, i.e. increasing coordination numbers and a decreasing degree of hydration when going from Mg to Ba. The dimensions of the structures range from hydrogen-bonded ions (3) over monomeric, neutral complex molecules (4, 5a), to polymeric networks (6). The successful isolation of the mixed-anion barium salt 8 adds a new facet to the coordination chemistry of violurate and related ligands.

Surprises in the Solvent-Induced Self-Ionization in the Uranium Tetrahalide UX4 (X = Cl, Br, I)/Ethyl Acetate System.

The reaction of the uranium(IV) halides UCl4, UBr4, or UI4 with ethyl acetate (EtOAc) leads to the formation of the complexes [UX3(EtOAc)4][UX5(EtOAc)] (X = Cl, Br) or [UI4(EtOAc)3]. Thus, both UCl4 and UBr4 show self-ionization in ethyl acetate to a distorted pentagonal bipyramidal [UX3(EtOAc)4]+ cation and a distorted octahedral [UX5(EtOAc)]- anion. Surprisingly, the chloride and bromide compounds are not isotypic. While [UCl3(EtOAc)4][UCl5(EtOAc)] crystallizes in the orthorhombic crystal system, space group P212121 at 250 K, the bromide compound crystallizes in the monoclinic crystal system, P121/n1 at 100 K. Unexpectedly, UI4 does not show self-ionization but forms [UI4(EtOAc)3] molecules, which crystallize in the monoclinic crystal system, P21/c, at 100 K. The compounds were characterized by single-crystal X-ray diffraction, IR, Raman, and NMR spectroscopy, as well as molecular quantum chemical calculations using solvent models.

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

Diphenylberyllium [Be3 Ph6 ] 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, HNPh2 and HPPh2 , 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 [Be3 (OtBu)6 ] and [Be(µ-NPh2 )Ph]2 have finally been verified and shown to be static in solution. Additionally [Be(µ-PPh2 )(HPPh2 )Ph]2 was generated, which is only the second beryllium-phospanide to be prepared; the stark differences between its behaviour and that of the analogous amide were also examined. The first crystalline example of a beryllium Grignard reagent with a non-bulky aryl group has also been prepared; it is stabilised with an N-heterocyclic carbene.

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)BeBr2] (1) and [(iPr)2BeBr2] (2) (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. The unusual bonding situation is understood from the results of energy decomposition analysis in combination with natural orbital for chemical valence and quantum theory of atoms-in-molecules analysis. The obtained findings shed light on the unusually high Be-C bond strength in carbene adducts to beryllium compounds and rationalize their geometry and reactivity.

s-Block chemistry in weakly coordinating solvents.

Alkaline earth metal catalysis has been a growing field in recent years. To enhance reactivity and to understand the metal-substrate interactions in more detail, reactions are increasingly carried out in weakly coordinating solvents. This article gives an overview over the two main approaches to facilitate this, which are either through the employment of highly dipolar haloaryls as solvents, or by increasing the solubility of the ligand systems. The resulting coordination modes and reactivities are presented together with the synthetic strategies. Additionally, the latest results of group 1 complex chemistry in aliphatic solvents are illustrated and future challenges are highlighted.

Quinolino[7,8-h]quinoline: a 'just right' ligand for beryllium(II) coordination.

We report the synthesis and crystal structure of the first quinolino[7,8-h]quinoline beryllium(II) complex of the general formula [BeL2(MeCN)Br]Br·MeCN, containing the ligand 4,9-dihydroxyquinolino[7,8-h]quinoline (L2). The Be(II) cation is a great size match for the dinitrogen binding pocket of the quinolino[7,8-h]quinoline ligand as indicated by minimal out-of-plane displacement and ligand distortion parameters.

Ligand Influence on Structural and Spectroscopic Properties of Beryllium Oxocarboxylates.

Aluminum-based adjuvants for vaccines and beryllium ions interact with the same immune receptor. The Be4O core, which is also found in beryllium oxocarboxylates, has been proposed to be the binding species in the latter case. However, this is not proven due to a lack of suitable probes for the Be4O moiety. Therefore, a versatile synthetic route to beryllium oxocarboxylates has been developed to investigate the steric and electronic influence of the ligands onto their molecular and spectroscopic properties. The oxocarboxylates exhibit extremely narrow line widths in 9Be NMR spectroscopy, and the chemical shift is only influenced by the sterics of the ligands. The mean variation of the atomic distances in the central Be4O building block is extremely small over all investigated compounds, and even the C-C distances are only little perturbed by the properties of the ligands. Vibrational spectroscopy showed Be-O bands; however, further distinctions could not be drawn.

Ethylenediamine complexes of the beryllium halides and pseudo-halides.

The suitability of ethylenediamine (en) as an alternative solvent to liquid ammonia in beryllium chemistry was evaluated. Therefore, BeF2, BeCl2, BeBr2, BeI2, [Be(NH3)4](N3)2, [Be(NH3)4](CN)2 and [Be(NH3)4](SCN)2 were reacted with ethylenediamine and analysed via NMR and IR spectroscopy. Additionally single crystal structures of [BeF2(en)]n, [Be(en)3]Cl2, [Be(en)3]Br2, [Be(en)2]I2·en, [Be(en)2](N3)2·en, [Be(en)2]4(SCN)7Cl and [Be3(OH)3(en)3][C2H9N2](SCN)4 were obtained. The anions were found to have a distinct influence on the solubility as well as on the species present in solution and the solid state, while ethylenediamine can act as mono- and bidentate ligand or as a crystal solvent.