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Organoberyllium is a Group 2 Alkali Earth Metal compound that is attached to an organic compound. Be is best known to be a +2 oxidation state and one of the smallest element and understudied in the periodic table. It is known to be highly reactive and extremely toxic and can cause berylliosis.[1][2] The Be 2+ cation is characterized by the highest known charge density (Z/r = 6.45), making it one of the hardest cations and a very strong Lewis acid.[3] It is most commonly used to coordinate other elements and can portray many types of compound through different ligands attachment. Coordination in Beryllium can range from two to four coordination compounds [4]Most common ligands attached to Beryllium are halides, hydride, methyl, aryl, alkyl in order to proceed to react with known organic compounds such as Beryllium borohydride in a 3 center 2 electron bond when forming and can cause a dimer, phosphine, N-hetereocyclic carbene (NHC), cyclic alkyl amino carbene (CAAC), and . It can best be prepared as a transmetallation or alkylation of Beryllium chloride[5].

Characteristic edit

Organoberyllium is comprised of a of Be with an organic compound attached. Be has a +2 oxidation state and can be is one of smallest element and understudied in the periodic table. There are very few reported case of a Be +1 and Be 0 oxidation state [6][7][8]. It has a higher charge density than any Group 2 element. Organoberyllium chemistry is limited to academic research due to the cost and toxicity of beryllium. Organometallic beryllium compounds are known to be highly reactive and strong acid. Beryllium have a high electronegativity compare to other Group 2 element thus resulting C-M bonds are less highly polarized and ionic-like [9]. The lighter organoberyllium compounds are often considered covalent, but with some ionic bond characteristics owning to the attached carbon bearing a negative dipole moment. This higher ionic character and bond polarization tends to produce high coordination numbers and many compounds (particularly dialklys) are polymeric in solid or liquid states with highly complex structures in solution, though in the gaseous state they are often monomeric.

Beryllium Compound edit

Organoberyllium can be form with a variety of compounds that can be used with ring structure, alkyl, alkynyls[10], hydride [11][12], methyl[13], halide, phosphine, and carbene. These compounds transform beryllium chemistry into many research avenue with coordination.

Ring Structures edit

Organoberyllium structures can consist of an aryl[14], dineopentylberyllium[14], beryllocene[15][16][17], phenyl[18], terphenyl[19]. These structure can be good coordination into other main group element and even possible metal centers.

Halide edit

Beryllium halide are formed by a combination of halogen with a beryllium atom. Beryllium are mostly covalent in nature except for flourine which is more ionic. They are known to form a four electron two center bond and can be use as a Lewis acid catalyst. Of most relevance to the current study are neutral Lewis base donor–acceptor adducts of beryllium dihalides. Preparation for these compound varies by the halogen. Organoberyllium Halide is one of the most common way to start a reaction to form any type of ligand[5][20]. Halides such as chloride, iodide, bromide are not limited to form with the Beryllium. Halide are able to donate 2 electrons into the Beryllium center with a charge of -1.

 
A Be complex with R not limited to Cl, I, Br, F
 

Phosphine edit

 
Phosphine type coordination with a Be Halide Complex [21]

Organoberyllium phosphine are another possible compound that is use in synthesis [21]. Phosphine donates 2 electrons and no charge into the Beryllium center. Phosphines are L-type ligands. Unlike most metal ammine complexes, metal phosphine complexes tend to be lipophilic, displaying good solubility in organic solvents. Phosphine ligands are also π-acceptors. Their π-acidity arises from overlap of P-C σ* anti-bonding orbitals with filled metal orbitals. Be can coordinate with a phosphine due to their good π-acceptors ability and is use extensively in Beryllium chemistry literature.

Carbene edit

Organoberyllium carbene consist of a carbene attached with a Be and can coordinate due to a two electron donation from a carbene compound to the Be. Carbene are able to donate 2 electron with a charge of no charge into the Beryllium center.

N-Hetereocyclic Carbene (NHC) edit

A Netereocyclic carbene Organoberyllium can proper coordinate with a N hetereocyclic Carbene (NHC) [22][23][24]. NHCs are defined as heterocyclic species containing a carbene carbon and at least one nitrogen atom within the ring structure [25] NHCs have found numerous applications in some of the most important catalytic transformations in the chemical industry, but their reactivity in coordinating with main group elements especially with Beryllium has potential as organocatalysts reactivity has opened up new areas of research.[25]

 
Coordination with a NHC ligand to a Be Complex with R not limited to halogen, hydride, phosphine, aryl, alkyl etc.

Cyclic Alkyl Amino Carbenes (CAAC) edit

Beryllium can coordinate with a Cyclic alkyl amino carbene (CAAC) ligand and can form a beryllium radical which can be present with a Beryllium complex (BR2) . A CAAC ligand contains a 2 electron -1 charge into the Beryllium center. [26] CAAC has an "amino" substituent and an "alkyl" sp3 carbon atom. CAACs are very good σ donors (higher HOMO) and π acceptors (lower LUMO) compared to NHCs. In addition, the lower heteroatom stability of the carbene center in CAAC compared to NHC results in a lower ΔE.

 
Coordination of a CAAC Ligand to a Be Complex with R not limited to halogen, hydride, methyl group, aryl and alkyl for coordination with Be


β-Diketiminate (NacNac) edit

NacNac is a class of anionic bidentate ligands. 1,3-Diketimines are often referred to as "HNacNac", a modification of the abbreviation Hacac used for 1,3-diketones. These species can exist as a mixture of tautomers. β-Diketiminates (BDI, also known as Nacnac), are a commonly-used class of supporting ligands that have been successfully adopted to stabilize an extensive range of metal ions from the s, p, d and f-blocks in multiple oxidation states. [27] The popularity of these monoanionic N-donor ligands can be mainly explained by their relatively convenient access and high stereoelectronic coordination. This enables the separation of highly reactive coordinatively unsaturated complexes. Moreover, recent studies have demonstrated the utility of this class of ligands for designing active catalysts for various transformations.

Synthesis edit

Synthesis for Beryllium is limited but literature have shown that Beryllium can be form when it is form as a halide, alkyl, alloxide and form with other organic compounds. Alkylation of Beryllium Halide is one of the most widely use method in Beryllium chemistry [28]

Transmetallation edit

A transmetallation involves a ligand transfer to one another such as this:

M'R2 + Be → BeR2 + M'


M is not limited to any main group and/or transition metal

R can be limited to almost any phosphine, aryl, alkyl, halogen, hydride and/or carbene.

In this case Organoberyllium can form such reaction such as:

Alkylation edit

Alkylation of Beryllium Halide is another common method to react to make an Organoberyllium compound such as this:

 
Structure of a Beryllocene with a Alkylation of a Beryllium Chloride

2MR1 + BeR2 → BeR1 + MR2

M is not limited to any main group and/or transition metal

R1 is not limited to Phenyl, Methyl, Methyl Oxide, carbene etc.

R2 can be any halide such as F, Br, I, Cl

An example of such reaction can be a Bis(cyclopentadienyl)beryllium (Cp2Be) or beryllocene reaction with BeCl2 such that:

2K[Cp]+BeCl2→(Cp)2Be + 2KCl


Be(I) and Be (0) Complex edit

While Be (II) is considered to be one of the more common oxidation states, there is also further research on a Be(I) and Be (0) complex. Low-valent main group compounds have recently become desirable synthetic targets due to their interesting reactivity comparable to transition metal complexes. In this work, stabilized cyclic (alkyl)(amino)carbene ligands were used to isolate and characterize the first neutral compounds containing the zero-valent s-block metal beryllium.[29] This was written in Nature Chemistry by Prof Holger Braunschweig and his group His Be (0) compound was stabilized by a strongly σ-donating and π-accepting cyclic CAAC ligand.

This reaction is shown when a CAAC Ligand is coordinated with a BeCl2 and using KC8 to form a zero oxidation Beryllium Complex.

This work was done by Prof Braunschweig to create the first neutral Be complex the R group includes Me and (CH2)5 and Dipp is otherwise known as 2,6-diisopropylphenyl.


Be(I) is another example of a rare phenomenon and few publications were reported. But one example of a Be(I) was a CAAC ligand already coordinated with Be. Prof Gilliard and his group created a more stable Be radical cation.[30] Because of well-established challenges concerning the reduction of Be (II) to Be(I), they pursued the radical via an oxidation strategy. They have use TEMPO in which in this case is a (2,2,6,6-Tetramethylpiperidin-1-yl) oxyl. This reaction resulted in a Be (I) compound just by stabilizing the Be radical.

Reaction shown is radical cation reaction from a Be (II) CAAC compound to a Be (I) CAAC compound.






See Also edit

Group 2 organometallic chemistry

Beryllium

Reference edit

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  21. ^ a b Buchner, Magnus R.; Müller, Matthias; Rudel, Stefan S. (2017-01-19). "Beryllium Phosphine Complexes: Synthesis, Properties, and Reactivity of (PMe 3 ) 2 BeCl 2 and (Ph 2 PC 3 H 6 PPh 2 )BeCl 2". Angewandte Chemie International Edition. 56 (4): 1130–1134. doi:10.1002/anie.201610956.
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  29. ^ Arrowsmith, Merle; Braunschweig, Holger; Celik, Mehmet Ali; Dellermann, Theresa; Dewhurst, Rian D.; Ewing, William C.; Hammond, Kai; Kramer, Thomas; Krummenacher, Ivo; Mies, Jan; Radacki, Krzysztof; Schuster, Julia K. (2016-09). "Neutral zero-valent s-block complexes with strong multiple bonding". Nature Chemistry. 8 (9): 890–894. doi:10.1038/nchem.2542. ISSN 1755-4349. {{cite journal}}: Check date values in: |date= (help)
  30. ^ Wang, Guocang; Walley, Jacob E.; Dickie, Diane A.; Pan, Sudip; Frenking, Gernot; Gilliard, Robert J. (2020-03-11). "A Stable, Crystalline Beryllium Radical Cation". Journal of the American Chemical Society. 142 (10): 4560–4564. doi:10.1021/jacs.9b13777. ISSN 0002-7863.
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