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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.

Reactivity of Diphenylberyllium as a Brønsted Base and Its Synthetic Application

Diphenylberyllium [Be₃Ph₆] 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.

Be3 Ru: Polar Multiatomic Bonding in the Closest Packing of Atoms

The new phase Be3 Ru crystallizes with TiCu3 -type structure (space group Pmmn (59), a=3.7062(1) Å, b=4.5353(1) Å, c=4.4170(1) Å), a coloring variant of the hexagonal closest packing (hcp) of spheres. The electronic structure revealed that Be3 Ru has a pseudo-gap close to the Fermi level. A strong charge transfer from Be to Ru was observed from the analysis of electron density within the Quantum Theory of Atoms in Molecules (QTAIM) framework and polar three- and four-atomic Be-Ru bonds were observed from the ELI-D (electron localizability indicator) analysis. This situation is very similar to the recently investigated Be5 Pt and Be21 Pt5 compounds. The unusual crystal chemical feature of Be3 Ru is that different charged species belong to the same closest packing, contrary to typical inorganic compounds, where the cationic components are located in the voids of the closest packing formed by anions. Be3 Ru is a diamagnet displaying metallic electrical resistivity.

Di(indenyl)beryllium

The bonding in beryllocene, [BeCp₂ ], took decades to establish, owing to its unexpected mixed hapticity structure (i.e., [Be(η⁵ -Cp)(η¹ -Cp)]). Beryllium complexes containing the indenyl ligand, which is a close relative of the cyclopentadienyl anion, but which is also known to exhibit its own bonding peculiarities (e.g., facile η⁵ ⇄ η³ shifts), have remained unknown. Standard metathetical approaches to their synthesis (e.g., with K[Ind'] + BeX₂ in an ether solvent) give rise to intractable oils from which nothing identifiable can be isolated. In contrast, mechanochemical preparation, involving the solvent-free grinding of BeBr₂ and potassium indenides, leads to the production of discrete (indenyl)beryllium complexes, including [Be(C₉ H₇ )₂ ] (1) and [Be{1,3-(SiMe₃ )₂ C₉ H₅ }Br] (2). The former displays η⁵ /η¹ -coordinated ligands in the solid state, but DFT calculations indicate that an η⁵ /η⁵ -conformation is less than 5 kcal mol^-1 higher in energy.

A Neutral Beryllium(I) Radical

The reduction of a cyclic alkyl(amino)carbene (CAAC)-stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, and UV/Vis spectroscopy, X-ray crystallography, and DFT calculations.

Formation and Characterization of BeFe(CO)4 - Anion with Beryllium-Iron Bonding

Heteronuclear BeFe(CO)₄ ^- anion complex is generated in the gas phase, which is detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The complex is characterized to have a Be-Fe bonded Be-Fe(CO)₄ ^- structure with C_3v symmetry and all of the four carbonyl ligands bonded on the iron center. Quantum chemical studies indicate that the complex has a quite short Be-Fe bond. Besides one electron-sharing σ bond, there are two additional, albeit weak, Be ← Fe(CO)₄ ^- dative π bonding interactions. The findings imply that metal-metal bonding between s-block and transition metals is viable under suitable coordination environment.

Diphenylberyllium Reinvestigated: Structure, Properties, and Reactivity of BePh2 , [(12-crown-4)BePh]+ , and [BePh3 ]. Chemistry 2020;26:9915-9922. [PMID: 31957173 PMCID: PMC7496417 DOI: 10.1002/chem.202000259]

The first synthesis of BePh2 was accomplished almost a century ago. However, its structure has remained unknown so far, while the corresponding aryls of the elements adjacent to beryllium in the periodic table are well investigated. Herein, we present an improved synthesis for diphenylberyllium and show by X-ray diffraction that it forms a trinuclear complex in the solid state. NMR spectroscopy revealed that this structure is also retained in solution but exhibits dynamic behavior. Its stability against heat and coordinating solvents is discussed and the possible obstacles to the synthesis of BePh2 from BeCl2 are examined. In the process of this study two ether adducts, BePh2 ⋅Et2 O and Be2 Ph4 ⋅Et2 O, have been characterized as well as the previously unknown triphenylberyllate anion. From the latter several single-crystal structures were obtained under various conditions, in which [BePh3 ]- is either isolated or acts as a ligand for Li+ . Furthermore, the crown ether induced selfionization of BePh2 is described and the resulting [(12-crown-4)BePh]+ cation was isolated, which shows an unusual 4+1 coordination around the Be atom.

Side-On Bonded Beryllium Dinitrogen Complexes

The preparation and spectroscopic identification of the complexes NNBe(η2 -N2 ) and (NN)2 Be(η2 -N2 ) and the energetically higher lying isomers Be(NN)2 and Be(NN)3 are reported. NNBe(η2 -N2 ) and (NN)2 Be(η2 -N2 ) are the first examples of covalently side-on bonded N2 adducts of a main-group element. The analysis of the electronic structure using modern methods of quantum chemistry suggests that NNBe(η2 -N2 ) and (NN)2 Be(η2 -N2 ) should be classified as π complexes rather than metalladiazirines.

Formation and Characterization of a BeOBeC Multiple Radical Featuring a Quartet Carbyne Moiety

Through reaction of beryllium dimers with carbon monoxide, a carbonyl complex BeBeCO is formed in solid neon. Upon visible light excitation, the BeBeCO complex rearranges to a BeCOBe isomer, which further isomerizes to a low-energy BeOBeC species under UV-visible light excitation. These species are identified on the basis of infrared absorption spectroscopy with isotopic substitutions and quantum chemical studies. The BeOBeC molecule is characterized to be a multiple radical species having an electronic quintet ground state featuring an unusual quartet carbyne unit with three unpaired electrons on the carbon center. Bonding analysis indicates that the strong Pauli repulsion between carbon 2s lone pair electrons and the σ electrons of the BeOBe fragment significantly weakens the Be-C bonding and destabilizes the triplet state of the BeOBeC radical with a doublet carbyne unit. The three-center π-bonding of BeOBe is also found to play a role in stabilizing the quartet carbyne.

Understanding the Localization of Berylliosis: Interaction of Be2+ with Carbohydrates and Related Biomimetic Ligands

The interplay of metal ions with polysaccharides is important for the immune recognition in the lung. Due to the localization of beryllium associated diseases to the lung, it is likely that beryllium carbohydrate complexes play a vital role for the development of berylliosis. Herein, we present a detailed study on the interaction of Be2+ ions with fructose and glucose as well as simpler biomimetic ligands, which emulate binding motives of saccharides. Through NMR and IR spectroscopy as well as single-crystal X-ray diffraction, complemented by competition reactions we were able to determine a distinctive trend in the binding affinity of these ligands. This suggests that under physiological conditions beryllium ions are only bound irreversibly in glycoproteins or polysaccharides if a quasi ideal tetrahedral environment and κ4 -coordination is provided by the respective biomolecule. Furthermore, Lewis acid induced conversions of the ligands and an extreme increase in the Brønstedt acidity of the present OH-groups imply that upon enclosure of Be2+ , alterations may be induced by the metal ion in glycoproteins or polysaccharides. In addition the frequent formation of Be-O-heterocycles indicates that multinuclear beryllium compounds might be the actual trigger of berylliosis. This investigation on beryllium coordination chemistry was supplemented by binding studies of selected biomimetic ligands with Al3+ , Zn2+ , Mg2+ , and Li+ , which revealed that none of these beryllium related ions was tetrahedrally coordinated under the give conditions. Therefore, studies on the metabolization of beryllium compounds cannot be performed with other hard cations as a substitute for the hazardous Be2+ .

Beryllium-Induced Conversion of Aldehydes

Aldehydes play a key role in the human metabolism. Therefore, it is essential to know their reactivity with beryllium compounds in order to assess its effects in the body. The reactivity of simple aldehydes towards beryllium halides (F, Cl, Br, I) was studied through solution and solid‐state techniques and revealed distinctively different reactivities of the beryllium halides, with BeF₂ being the least and BeI₂ the most reactive. Rearrangement and aldol condensation reactions were observed and monitored by in situ NMR spectroscopy. Crystal structures of various compounds obtained by Be²⁺‐catalyzed cyclization, rearrangement, and aldol addition reactions or ligation of beryllium halides have been determined, including unprecedented one‐dimensional BeCl₂ chains and the first structurally characterized example of an 1‐iodo‐alkoxide. Long‐term studies showed that only aldehydes without a β‐H can form stable beryllium complexes, whereas other aldehydes are oligo‐ and polymerized or decomposed by beryllium halides.