Neutral zero-valent s-block complexes with strong multiple bonding

Base-stabilized formally zero-valent mono and diatomic molecular main-group compounds

Various compounds are known for transition metals in their formal zero-oxidation state, while similar compounds of main-group elements are recently realized and limited to only a few examples. Lewis-base-stabilized mono and diatomic molecular species (B₂, C, C₂, Si, Si₂, Ge, Ge₂, Sn, P₂, As₂, Sb₂) represent groundbreaking examples of main-group compounds with formally zero-oxidation state. In recent years, the isolation of low-valent main-group compounds has attracted increasing attention of both experimental and theoretical chemists. This is not only due to their fascinating electronic structures and exceptional reactivities, but also their use as valuable precursors for the synthesis of exotic yet important chemical species. This has led to a better understanding of the intricate balance of the donor-acceptor properties of the ligand(s) used to stabilize elements in a formally zero-oxidation state. Owing to the unusual oxidation state of the central element, many compounds containing formally zero-valent elements can efficiently activate otherwise inert small molecules. This review describes the synthesis, characterization, and reactivity of reported mono and diatomic formal zero-oxidation state main-group compounds. This review also emphasizes the comparative description of systems where different ligands are used to stabilize an element in its formal zero-oxidation state.

Three-center two-electron bonds from the quantum interference perspective

The nature of the three-center two-electron (3c2e) chemical bond is investigated by the Interference Energy Analysis (IEA) method and using of a SC(2, 3) (spin coupled wave function with two...

Impact of the coordination of multiple Lewis acid functions on the electronic structure and vn configuration of a metal center

The covalent bond classification (CBC) method represents a molecule as ML_lX_xZ_z by evaluating the total number of L, X and Z functions interacting with M. The CBC method is a simplistic approach that is based on the notion that the bonding of a ligating atom (or group of atoms) can be expressed in terms of the number of electrons it contributes to a 2-electron bond. In many cases, the bonding in a molecule of interest can be described in terms of a 2-center 2-electron bonding model and the ML_lX_xZ_z classification can be derived straightforwardly by considering each ligand independently. However, the bonding within a molecule cannot always be described satisfactorily by using a 2-center 2-electron model and, in such situations, the ML_lX_xZ_z classification requires a more detailed consideration than one in which each ligand is treated in an independent manner. The purpose of this article is to provide examples of how the ML_lX_xZ_z classification is obtained in the presence of multicenter bonding interactions. Specific emphasis is given to the treatment of multiple π-acceptor ligands and the impact on the vⁿ configuration, i.e. the number of formally nonbonding electrons on an element of interest.

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.

Be-Be π bonding and predicted superconductivity in MBe2 (M=Zr, Hf)

Beryllium, an s-block element, forms an aromatic network of delocalized Be-Be π bonds in alloys ZrBe2 and HfBe2. This gives rise to a structure that fits description as stacked [Be2]4- layers with tetravalent cations in between. The [Be2]4- sublattice is isoelectronic and isostructural to graphite, as well as the [B]-2 sublattice in MgB2, and it bears identical manifestations of π bonding in its electronic band structure. These come in the form of degeneracies at K and H in the Brillouin zone, separated in energy as the result of interlayer orbital interactions. Zr and Hf use their valence d orbitals to form bonds with the layers, leading to nearly identical band structures. Like MgB2, ZrBe2 and HfBe2 are computed to be phonon-mediated superconductors at ambient pressures, with respective critical temperatures of 11.4 K and 8.8 K. The coupling strength between phonons and free electrons is very similar, so that the difference in critical temperatures is controlled by the mass of constituent interlayer ions.

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.

New horizons in low oxidation state group 2 metal chemistry

Since the seminal report on Mg in the +I oxidation state in 2007, low-valent complexes featuring a Mg^I-Mg^I bond developed from trophy molecules to state-of-the-art reducing agents. Despite increasing interest in low-valency of the other group 2 metals, this area was restricted for a long time to a rare example of a Ca^I(arene)Ca^I inverse sandwich. This feature article focuses on the most recent developments in the field, highlighting recent breakthroughs for Be, Mg and Ca. The more exotic metal Be was the first to be isolated as a zero-valent complex which could be oxidized to a Be^I species. There also has been interest in breaking the Mg^I-Mg^I bond with superbulky β-diketiminate ligands (BDI) that suppress (BDI)Mg-Mg(BDI) bond formation. This led to Mg-Mg bond elongation or Mg-N bond cleavage. Several reports on attempts to isolate (BDI)Mg˙ radicals by combinations of ligand bulk, addition of neutral ligands or UV(vis) irradiation led to reduction of the aromatic solvents, underscoring the high reactivity of these open shell species. Only recently, zero-valent complexes of Mg were introduced. Double reduction of a (BDI)MgI complex with Na gave [(BDI)Mg^-]Na⁺. This Mg⁰ complex crystallized as a dimer in which the Na⁺ cations bridge the two (BDI)Mg^- anions which react as Mg nucleophiles. Thermal decomposition led to spontaneous formation of Na⁰ and a trinuclear (BDI)MgMgMg(BDI) complex. This mixed-valence Mg₃-complex is a prime example of the fleeting multinuclear Mg_n intermediates discussed on the way from Mg metal to Grignard reagent. Attempts to prepare low-valent Ca^I compounds by reduction of (BDI)CaI led to dearomatization of the arene solvents: (BDI)Ca(arene)Ca(BDI). Reduction in alkanes prevented this decomposition pathway but led to N₂ reduction and isolation of (BDI)Ca(N₂)Ca(BDI), representing the first example of molecular nitrogen fixation with an early main group metal. As the N₂^2- anion reacts in most cases as a very strong two-electron reductant, LCa(N₂)CaL could be seen as a synthon for hitherto elusive Ca^I-Ca^I complexes. Theoretical calculations suggest that participation of Ca d-orbitals is relevant for N₂ activation. These most recent developments in low-valent group 2 metal chemistry will revive this area and undoubtly lead to new reactivities and applications.

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.

Recent advances in the chemistry and applications of N-heterocyclic carbenes

N-Heterocyclic carbenes, despite being isolated and characterized three decades ago, still capture scientists' interest as versatile, modular and strongly coordinating moieties. In the last decade, driven by the increasingly refined fundamental understanding of their behaviour, the emergence of new carbene frameworks and cogent sustainability issues, N-heterocyclic carbenes have experienced a tremendous increase in utilization across several disparate fields. In this Review, a concise overview of N-heterocyclic carbenes encompassing their history, properties and applications in transition metal catalysis, on-surface chemistry, main group chemistry and organocatalysis is provided. Emphasis is placed on developments emerging in the last seven years and on envisaging future directions.

Taming the Antiferromagnetic Beast: Computational Design of Ultrashort Mn-Mn Bonds Stabilized by N-Heterocyclic Carbenes

The development of complexes featuring low-valent, multiply bonded metal centers is an exciting field with several potential applications. In this work, we describe the design principles and extensive computational investigation of new organometallic platforms featuring the elusive manganese-manganese bond stabilized by experimentally realized N-heterocyclic carbenes (NHCs). By using DFT computations benchmarked against multireference calculations, as well as MO- and VB-based bonding analyses, we could disentangle the various electronic and structural effects contributing to the thermodynamic and kinetic stability, as well as the experimental feasibility, of the systems. In particular, we explored the nature of the metal-carbene interaction and the role of the ancillary η6 coordination to the generation of Mn2 systems featuring ultrashort metal-metal bonds, closed-shell singlet multiplicities, and positive adiabatic singlet-triplet gaps. Our analysis identifies two distinct classes of viable synthetic targets, whose electrostructural properties are thoroughly investigated.

Transition-Metal Chemistry of the Heavier Alkaline Earth Atoms Ca, Sr, and Ba

ConspectusAlkaline earth elements beryllium, magnesium, calcium, strontium, and barium with an ns² valence-shell configuration are usually classified as main-group elements that belong to the s-block atoms. For a long time, the elements were considered to be rather chemically uninteresting atomic species due to preconceived ideas about bonding, structure, and reactivity. They typically use the two ns valence electrons in forming ionic salt compounds with the metal in a formal oxidation state of +2. For the heavier alkaline earth atoms, calcium, strontium, and barium, their (n - 1)d atomic orbitals (AOs) are empty but lie close in energy to the valence np orbitals. Earlier theoretical investigations have already suggested that these elements can employ the (n - 1)d AOs to some extent to form polar bonds in divalent species in which the alkaline earth metal centers are sufficiently positively charged. The d orbital involvement increases from Ca to Sr and markedly in Ba. Thus, barium has been termed an honorary transition metal.Recently, molecular complexes of Ca, Sr, and Ba were prepared in the gas phase and in a low-temperature solid neon matrix and were detected by infrared spectroscopy. An analysis of the electronic structures of [Ba(CO)]⁺, [Ba(CO)]^-, saturated coordinated octacarbonyls [M(CO)₈] and [M(CO)₈]⁺, isoelectronic dinitrogen complexes [M(N₂)₈] and [M(N₂)₈]⁺, and the tribenzene complexes [M(Bz)₃] (M = Ca, Sr, Ba) revealed that the metal-ligand bonding can be straightforwardly discussed using the traditional Dewar-Chatt-Duncanson (DCD) model as in classical transition-metal complexes. The metal-ligand bonds can be explained with metal → ligand π back donation from occupied metal (n - 1)d AOs to vacant antibonding π molecular orbitals of the ligands with concomitant σ donation from occupied MOs of the ligands to vacant metal d orbitals of the alkaline earth atoms. In addition, heteronuclear Ca-Fe carbonyl cation complexes were also produced in the gas phase. Bonding analysis of the coordination saturated [CaFe(CO)₁₀]⁺ complex implies that it can be described by the bonding interactions between a [Ca(CO)₆]²⁺ fragment and an [Fe(CO)₄]^- anion fragment in forming a Fe → Ca d-d dative bond. The nature of metal-ligand and metal-metal bonding was quantitatively elucidated by the energy decomposition analysis in conjunction with the natural orbitals for the chemical valence (EDA-NOCV) method, which indicate that the (n - 1)d AOs of the alkaline earth metals are the dominant orbitals participating in the covalent interactions, just as typical transition metals. The results indicate that the heavier alkaline earth elements have a much richer covalent chemistry than previously thought. These findings, along with earlier studies, suggest that the heavier alkaline earth atoms Ca, Sr, and Ba should be classified as transition metals rather than main group atoms in the periodic table of the elements. This interesting structural chemistry, together with some recently reported examples of spectacular reactivity, establishes these elements as exciting and promising research targets in current research.

Highly Coordinated Heteronuclear Calcium-Iron Carbonyl Cation Complexes [CaFe(CO)n ]+ (n=5-12) with d-d Bonding

Heteronuclear calcium-iron carbonyl cation complexes in the form of [CaFe(CO)n ]+ (n=5-12) are produced in the gas phase. Infrared photodissociation spectroscopy in conjunction with quantum chemical calculations confirm that the n=10 complex is the coordination saturated ion where a Fe(CO)4 fragment is bonded with a Ca(CO)6 fragment through two side-on bridging carbonyl ligands. Bonding analysis indicates that it is best described by the bonding interactions between a [Ca(CO)6 ]2+ dication and an [Fe(CO)4 ]- anion forming a Fe→Ca d-d dative bond in the [(CO)6 Ca-Fe(CO)4 ]+ structure, which enriches the pool of experimentally observed complexes of calcium that mimic transition metal compounds. The molecule is the first example of a heteronuclear carbonyl complex featuring a d-d bond between calcium and a transition metal.

N-Heterocyclic carbene, carbodiphosphorane and diphosphine adducts of beryllium dihalides: synthesis, characterisation and reduction studies

Reaction of several N-heterocyclic carbenes, a carbodiphosphorane, and bis(diphenylphosphino)ethane (DPPE) with [BeX2(OEt2)2] (X = Br or I) have yielded a variety of beryllium dihalide adduct complexes, all of which were crystallographically characterised. Attempts to reduce the compounds to low oxidation state beryllium complexes using a variety of reducing agents have been carried out, but were of limited success. However, reaction of [(IPr)BeBr2] (IPr = :C{(DipNCH)2}; Dip = 2,6-diisopropylphenyl) with the aluminium(i) heterocycle, [:Al(DipNacnac)] (DipNacnac = [HC(MeCNDip)2]-) afforded the adduct complex, [{(IPr)(Br)Be(μ-H)}2], while reduction of [(IPr)BeBr2] with potassium naphthalenide gave the beryllium naphthalenediyl complex, [(IPr)Be(C10H8)]. Furthermore, reaction of [{(DPPE)BeI2}∞], with [:Al(DipNacnac)] led to insertion of the Al centre of the heterocycle into a Be-I bond, and formation of a rare example of an Al-Be bonded complex, [(DPPE)(i)Be-Al(i)(DipNacnac)].

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.

s-Block Multiple Bonds: Isolation of a Beryllium Imido Complex

A common feature of d- and p-block elements is that they participate in multiple bonding. In contrast, the synthesis of compounds containing homo- or hetero-nuclear multiple bonds involving s-block elements is extremely rare. Herein, we report the synthesis, molecular structure, and computational analysis of a beryllium imido (Be=N) complex (2), which was prepared via oxidation of a molecular Be⁰ precursor (1) with trimethylsilyl azide Me₃ SiN₃ (TMS-N₃ ). Notably, compound 2 features the shortest known Be=N bond (1.464 Å) to date. This represents the first compound with an s-block metal-nitrogen multiple bond. All compounds were characterized experimentally with multi-nuclear NMR spectroscopy (¹ H, ¹³ C, ⁹ Be) and single-crystal X-ray diffraction studies. The bonding situation was analyzed with density functional theory (DFT) calculations, which supports the existence of π-bonding between beryllium and nitrogen.

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.

Strongly reducing magnesium(0) complexes

A complex of a metal in its zero oxidation state can be considered a stabilized, but highly reactive, form of a single metal atom. Such complexes are common for the more noble transition metals. Although rare examples are known for electronegative late-main-group p-block metals or semimetals^1-6, it is a challenge to isolate early-main-group s-block metals in their zero oxidation state^7-11. This is directly related to their very low electronegativity and strong tendency to oxidize. Here we present examples of zero-oxidation-state magnesium (that is, magnesium(0)) complexes that are stabilized by superbulky, monoanionic, β-diketiminate ligands. Whereas the reactivity of an organomagnesium compound is typically defined by the nucleophilicity of its organic groups and the electrophilicity of Mg²⁺ cations, the Mg⁰ complexes reported here feature electron-rich Mg centres that are nucleophilic and strongly reducing. The latter property is exemplified by the ability to reduce Na⁺ to Na⁰. We also present a complex with a linear Mg₃ core that formally could be described as a Mg^I-Mg⁰-Mg^I unit. Such multinuclear mixed-valence Mg_n clusters are discussed as fleeting intermediates during the early stages of Grignard reagent formation. Their remarkably strong reducing power implies a rich reactivity and application as specialized reducing agents.

Twisting versus Delocalization in CAAC- and NHC-Stabilized Boron-Based Biradicals: The Roles of Sterics and Electronics

Twisted boron-based biradicals featuring unsaturated C2 R2 (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C2 R2 -bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.

Isolation and Reactivity of an Antiaromatic s-Block Metal Compound

The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation-state flexibility of the s-block metals has long stood in the way of their participation in sophisticated π-bonding arrangements, and truly antiaromatic systems containing s-block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis-base-coordination chemistry.

Revisiting the Bonding Scenario of Two Donor Ligand Stabilized C2 Species

Quantum chemical calculations using density functional methods were performed for complexes of type L₂C₂ with L = NHC^Me (1), SNHC^Me (2) (S = saturated), cAAC^Me (3), and diamidocarbene (DAC^Me) (4). The equilibrium structures of 1-4 possess almost linear C₄ cores. A high thermochemical stability of the complexes with respect to dissociation, L₂C₂ → C₂ + 2L, is indicated by the large bond dissociation energy following the order 3 > 4 > 2 > 1. The results show that the use of SNHC^Me and DAC^Me as ligands is preferable over NHC^Me. The bonding analysis using charge and energy decomposition methods reveals that (cAAC^Me)₂C₂ and (DAC^Me)₂C₂ possess genuine cumulene C₄ moieties, which results from the electron-sharing bonding between quintet L₂ and quintet C₂ fragments. In contrast, the bonding in (NHC^Me)₂C₂ and (SNHC^Me)₂C₂ comes from a combination of dative and electron-sharing interactions between doublet L₂⁺ and doublet C₂^- fragments.

Stabilization of Linear C3 by Two Donor Ligands: A Theoretical Study of L-C3 -L (L=PPh3 , NHCMe , cAACMe )*

Quantum chemical studies using density functional theory and ab initio methods have been carried out for the molecules L-C3 -L with L=PPh3 (1), NHCMe (2, NHC=N-heterocyclic carbene), and cAACMe (3, cAAC=cyclic (alkyl)(amino) carbene). The calculations predict that 1 and 2 have equilibrium geometries where the ligands are bonded with rather acute bonding angles at the linear C3 moiety. The phosphine adduct 1 has a synclinal (gauche) conformation whereas 2 exhibits a trans conformation of the ligands. In contrast, the compound 3 possesses a nearly linear arrangement of the carbene ligands at the C3 fragment. The bond dissociation energies of the ligands have the order 1<2<3. The bonding analysis using charge and energy decomposition methods suggests that 3 is best described as a cumulene with electron-sharing double bonds between neutral fragments (cAACMe )2 and C3 in the respective electronic quintet state yielding (cAACMe )=C3 =(cAACMe ). In contrast, 1 and 2 possess electron-sharing and dative bonds between positively charged ligands [(PPh3 )2 ]+ or [(NHCMe )2 ]+ and negatively charged [C3 ]- fragments in the respective doublet state.

The Valence Orbitals of the Alkaline-Earth Atoms

Quantum chemical calculations of the alkaline-earth oxides, imides and dihydrides of the alkaline-earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca6 H9 [N(SiMe3 )2 ]3 (pmdta)3 (pmdta=N,N,N',N'',N''-pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n-1)d orbitals. The alkaline-earth metals Be and Mg build covalent bonds like typical main-group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline-earth metals, but are also very important for understanding and designing experimental studies.

Behavior of beryllium halides and triflate in acetonitrile solutions

The solution behavior of beryllium halides and triflate in acetonitrile was studied by NMR, IR and Raman spectroscopy. Thereby mononuclear units [(MeCN)2BeX 2] (X = Cl, Br, I, OTf) were identified as dominant species in these solutions. The solid state structure of [(MeCN)2Be(OTf)2] has been determined by X-ray diffraction. If only one equivalent of MeCN is used the dinuclear compounds [(MeCN)BeX 2]2 (X = Cl, Br, I) are formed. Partial halide and triflate dissociation into the monomeric complexes as well as the formation of hetero-halide complexes [(MeCN)2BeClBr], [(MeCN)2BeClI] and [(MeCN)2BeBrI] was observed.

Theoretical study of boron, beryllium and lithium clusters (n=2-6), adsorption on graphitic carbon nitride and the study of acceptor-donor orbital of the coordination of a styrene molecule on [cluster/g-C3N4] systems

The adsorption of boron, beryllium and lithium clusters on graphitic carbon nitride g-C₃N₄, and the adsorption of styrene molecule on the B, Be, Li cluster/g-C₃N₄ sheet have been investigated through the density functional theory (DFT) calculations. Our calculations show distortion of the geometry of the clusters when coordinating with the g-C₃N₄ sheet. Boron (n = 5 and 6), beryllium (n = 2-4, 6) and Li₃ cluster on g-C₃N₄ present characteristics to adsorb a styrene molecule. The styrene on Be₄/g-C₃N₄ system exhibits better adsorption, due to the beryllium atoms have strong interactions with the π-orbitals of the aromatic ring of the styrene molecule. The study of natural bond orbitals of styrene-cluster/g-C₃N₄ systems showed the donation process from the styrene molecule and the g-C₃N₄ sheet towards the boron, beryllium and lithium clusters. Only back donation was observed the boron and beryllium clusters.

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.

Hungry for charge – how a beryllium scorpionate complex “eats” a weakly coordinating anion

We present the reaction of a tris(pyrazolyl) beryllium scorpionate (TpBe) complex with a weakly coordinating anion (WCA), which yields the heteroleptic complex TpBeOC(CF3)3 1 (TpBeOR F). The product 1 has been characterized by multinuclear NMR spectroscopy (1H, 9Be, 13C) and single-crystal X-ray diffraction (scXRD). Quantum chemical calculations (DFT, NPA, LOL) were performed to study the bonding nature in 1.

Crystallographic study of a heteroleptic chloroberyllium borohydride carbodicarbene complex

Interest in beryllium, the lightest member of group 2 elements, has grown substantially within the synthetic community. Herein, we report the synthesis and crystal structure of a heteroleptic haloberyllium borohydride bis(1-isopropyl-3-methyl-benzimidazol-2-ylidene)methane ‘carbodicarbene’ (CDC) complex [(CDC)BeCl(BH4)]. Crystallographic data: Triclinic space group P1̅, a = 8.8695(14), b = 12.394(2), c = 16.844(3) Å, α = 102.395(4), β = 96.456(4), γ = 99.164(4)°, wR2 (all data) = 0.2706 for 6720 unique data and 357 refined parameters.

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.