Disilicon-Mediated Carbon Monoxide Activation: From a 1,2,3-Trisila- to 1,3-Disilacyclopentadienes with Hypercoordinate λ4Si-λ3C Double Bonds

The facile reaction of the SiPh2-bridged bis-silylene (LSi:)2SiPh2 (L=PhC(NBut)2) with diphenylacetylene affords the unprecedented 1,2,3-trisilacyclopentadiene (LSi)2(PhC)2SiPh2 1 with a hypercoordinate λ4Si-λ3Si double bond. Compound 1 is very oxophilic and consumes three molar equivalents of inert N2O to form the bicyclic oxygenation product 2 through O-atom insertion in the Si=Si and Si-Si bonds. Strikingly, 1 can completely split the C≡O bonds of carbon monoxide under ambient conditions (1 atm, room temperature), yielding the 1,3-disilacyclopentadiene 3, representing the first hypercoordinate example of a cyclosilene with a λ4Si-λ3C double bond. Likewise, reaction of Xyl-NC (Xyl=2,6-dimethylphenyl), an isocyanide isoelectronic with CO, with 1 furnishes the related 1,3-disilacyclopentadiene 4 but with an amidinato silylene pendent attached to the Si=C carbon ring atom.

Trapping an Elusive Phosphanyl-Phosphaalumene

We describe our efforts to access a compound with an Al=P double bond by reaction of Al(Nacnac) towards [H2CN(Dipp)]2P(PCO) (Nacnac=HC[C(Me)N(Dipp)]2; Dipp=2,6-iPr2C6H3). Our observations are consistent with the formation of a transient phosphanyl-phosphaalumene at low temperatures (-70 °C), however this species was found to readily undergo intramolecular C-H activation of the β-diketiminato ligand upon warming to room temperature. The reactivity of the transient complex toward small molecules including dihydrogen, carbon dioxide, phosphaketenes, amines and silanes could be explored at low temperatures, showcasing that the target compound can react as both a frustrated Lewis pair (via the pendant phosphanyl moiety) or in hydroelementation reactions of the Al=P bond. The elusive target molecule could be trapped by addition of a Lewis base (tetrahydrofuran) affording an isolable molecular species that reacts in an analogous fashion to the base-free compound.

Reductive Coupling of a Diazoalkane Derivative Promoted by a Potassium Aluminyl and Elimination of Dinitrogen to Generate a Reactive Aluminium Ketimide

The reaction of 9-diazo-9H-fluorene (fluN2 ) with the potassium aluminyl K[Al(NON)] ([NON]2- =[O(SiMe2 NDipp)2 ]2- , Dipp=2,6-iPr2 C6 H3 ) affords K[Al(NON)(κN1 ,N3 -{(fluN2 )2 })] (1). Structural analysis shows a near planar 1,4-di(9H-fluoren-9-ylidene)tetraazadiide ligand that chelates to the aluminium. The thermally induced elimination of dinitrogen from 1 affords the neutral aluminium ketimide complex, Al(NON)(N=flu)(THF) (2) and the 1,2-di(9H-fluoren-9-yl)diazene dianion as the potassium salt, [K2 (THF)3 ][fluN=Nflu] (3). The reaction of 2 with N,N'-diisopropylcarbodiimide (iPrN=C=NiPr) affords the aluminium guanidinate complex, Al(NON){N(iPr)C(N=CMe2 )N(CHflu)} (4), showing a rare example of reactivity at a metal ketimide ligand. Density functional theory (DFT) calculations have been used to examine the bonding in the newly formed [(fluN2 )2 ]2- ligand in 1 and the ketimide bonding in 2. The mechanism leading to the formation of 4 has also been studied using this technique.

Low-Coordinate Magnesium Sulfide and Selenide Complexes

The reactions of [{(iPrDipNacNac)Mg}2] 1 (iPrDipnacnac = HC(iPrCNDip)2) with Ph3P═O at 100 °C afforded the phosphinate complex [(iPrDipNacNac)Mg(OPPh3)(OPPh2)] 3. Reactions of 1 with Ph3P═E (E = S, Se) proceeded rapidly at room temperature to low-coordinate chalcogenide complexes [{(iPrDipNacNac)Mg}2(μ-S)] 4 and [{(iPrDipNacNac)Mg}2(μ-Se)] 5, respectively. Similarly, reactions of RNHC═S ((MeCNR)2C═S with R = Me, Et, or iPr) with 1 afforded NHC adducts of magnesium sulfide complexes, [{(iPrDipNacNac)Mg(RNHC)}(μ-S){Mg(iPrDipNacNac)}] 6, that could alternatively be obtained by adding the appropriate RNHC to sulfide complex 4. Complex 4 reacted with 1-adamantylazide (AdN3) to give [{(iPrDipNacNac)Mg}2(μ-SN3Ad)] 7 and can form various simple donor adducts in solution, of which [(iPrDipNacNac)Mg(OAd)}2(μ-S)] 8a (OAd = 2-adamantanone) was structurally characterized. The nature of the ionic Mg-E-Mg unit is described by solution and solid-state studies of the complexes and by DFT computational investigations.

Anions featuring an aluminium-silicon core with alumanyl silanide and aluminata-silene characteristics

Molecular species containing multiple bonds to aluminium have long been challenging synthetic targets. Despite recent landmark discoveries in this area, heterodinuclear Al-E multiple bonds (where E is a group-14 element) have remained rare and limited to highly polarized π-interactions (Al=E ↔ +Al-E-). Here we report the isolation of three alumanyl silanide anions that feature an Al-Si core stabilized by bulky substituents and a Si-Na interaction. Single-crystal X-ray diffraction studies, spectroscopic analysis and density functional theory calculations show that the Al-Si interaction possesses partial double bond character. Preliminary reactivity studies support this description of the compounds through two resonance structures: one that displays a predominant nucleophilic character of the sodium-coordinated silicon centre in the Al-Si core, as shown by silanide-like reactivity towards halosilane electrophiles and the CH-insertion of phenylacetylene. Moreover, we report an alumanyl silanide with a sequestered sodium cation. Cleavage of the Si-Na bond by [2.2.2]cryptand increases the double bond character of the Al-Si core to produce an anion with high aluminata-silene (-Al=Si) character.

Crystalline Neutral Aluminum Selenide/Telluride: Isoelectronic Aluminum Analogues of Carbonyls

Neutral aluminum chalcogenides (R-Al(L)═Ch; L = ligand, Ch = chalcogen), stabilized by a Lewis base ligand, represent isoelectronic counterparts to carbonyl compounds and have long been pursued for isolation. Herein, we present the synthesis of an aluminum selenide, [N]-Al(ⁱPr₂-bimy)═Se, and an aluminum telluride, [N]-Al(ⁱPr₂-bimy)═Te, under ambient conditions ([N] = 1,8-bis(3,5-di-tert-butylphenyl)-3,6-di-tert-butylcarbazolyl; ⁱPr₂-bimy = 1,3-diisoproplylbenzimidazole-2-ylidene). These compounds arise from the oxidation reaction of [N]-Al(ⁱPr₂-bimy) with Se and (ⁿBu)₃P═Te, respectively. One notable characteristic of the Al and Ch interaction is the presence of an Al-Ch σ bond, strengthened by the electrostatic attraction between the Al⁺ and Ch^- centers as well as the donation of lone pairs from Ch into vacant orbitals at Al. This results in an Al-Ch multiple bond with an ambiphilic nature. Preliminary investigations into their reactivity unveil their remarkable propensity for facile (cyclo)addition reactions with diverse substrates, including PhCCH, PhCN, AdN₃, MeI, PhSiH₃, and C₆F₆, leading to the formation of unprecedented main group heterocycles and alumachalcogenides.

Three-Membered Aluminacycles

Three-membered-ring scaffolds of carbocycles, namely, cyclopropanes and cyclopropenes, are ubiquitous in natural products and pharmaceutical molecules. These molecules exhibit a peculiar reactivity, and their applications as synthetic intermediates and versatile building blocks in organic synthesis have been extensively studied over the past century. The incorporation of heteroatoms into three-membered cyclic structures has attracted significant attention, reflecting fundamental differences in their electronic/geometric structures and reactivities compared to their carbon congeners and their associated potential for exploitation in applications. Recently, the chemistry of low-valent aluminum species, alumylenes, dialumenes, and aluminyl anions, has dramatically developed, which has allowed access to hitherto unprecedented aluminacycles. This Perspective focuses upon advances in the chemistry of three-membered aluminacycles, including their synthetic protocols, spectroscopic and structural properties, and reactivity toward various substrates and small molecules.

An Aluminum Telluride with a Terminal Al=Te Bond and its Conversion to an Aluminum Tellurocarbonate by CO2 Reduction

Facile access to dimeric heavier aluminum chalcogenides [(NHC)Al(Tipp)-μ-Ch]₂ (NHC=IiPr (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, IMe₄ (1,3,4,5-tetramethylimidazol-2-ylidene); Tipp=2,4,6-iPr₃ C₆ H₂ ; Ch=Se, Te) by treatment of NHC-stabilized aluminum dihydrides with elemental Se and Te is reported. The higher affinity of IMe₄ in comparison with IiPr toward the Al center in [(NHC)Al(Tipp)-μ-Ch]₂ can be used for ligand exchange. Additionally, the presence of excess IMe₄ allows for cleavage of the dimers to form a rare example of a neutral multiply bonded heavier aluminum chalcogenide in the form of a tetracoordinate aluminum complex, (IMe₄ )₂ (Tipp)Al=Te. This species reacts with three equivalents of CO₂ across two Al-C^NHC and the Al=Te bond affording a pentacoordinate aluminum complex containing a dianionic tellurocarbonate ligand [CO₂ Te]^2- , which is the first example of tellurium analogue of a carbonate [CO₃ ]^2- .

The emerging chemistry of the aluminyl anion

The chemistry of low valent p-block metal complexes continues to elicit interest in the research community, demonstrating reactivity that replicates and in some cases exceeds that of their more widely studied d-block metal counterparts. The introduction of the first aluminyl anion, a complex containing a formally anionic Al(I) centre charge balanced by an alkali metal (AM) cation, has established a platform for a new area of chemical research. The chemistry displayed by aluminyl compounds is expanding rapidly, with examples of reactivity towards a diverse range of small molecules and functional groups now reported in the literature. Herein we present an account of the structure and reactivity of the growing family of aluminyl compounds. In this context we examine the structural relationships between the aluminyl anion and the AM cations, which now include examples of AM = Li, Na, K, Rb and Cs. We report on the ability of these compounds to engage in bond-breaking and bond-forming reactions, which is leading towards their application as useful reagents in chemical synthesis. Furthermore we discuss the chemistry of bimetallic complexes containing direct Al-M bonds (M = Li, Na, K, Mg, Ca, Cu, Ag, Au, Zn) and compounds with Al-E multiple bonds (E = NR, CR₂, O, S, Se, Te), where both classes of compound are derived directly from aluminyl anions.

Carbon-chalcogen bond formation initiated by [Al(NONDipp)(E)]- anions containing Al-E{16} (E{16} = S, Se) multiple bonds

Multiply-bonded main group metal compounds are of interest as a new class of reactive species able to activate and functionalize a wide range of substrates. The aluminium sulfido compound K[Al(NONDipp)(S)] (NONDipp = [O(SiMe2NDipp)2]2-, Dipp = 2,6-iPr2C6H3), completing the series of [Al(NONDipp)(E)]- anions containing Al-E{16} multiple bonds (E{16} = O, S, Se, Te), was accessed via desulfurisation of K[Al(NONDipp)(S4)] using triphenylphosphane. The crystal structure showed a tetrameric aggregate joined by multiple K⋯S and K⋯π(arene) interactions that were disrupted by the addition of 2.2.2-cryptand to form the separated ion pair, [K(2.2.2-crypt)][Al(NONDipp)(S)]. Analysis of the anion using density functional theory (DFT) confirmed multiple-bond character in the Al-S group. The reaction of the sulfido and selenido anions K[Al(NONDipp)(E)] (E = S, Se) with CO2 afforded K[Al(NONDipp)(κ2 E,O-EC{O}O)] containing the thio- and seleno-carbonate groups respectively, consistent with a [2 + 2]-cycloaddition reaction and C-E bond formation. An analogous cycloaddition reaction took place with benzophenone affording compounds containing the diphenylsulfido- and diphenylselenido-methanolate ligands, [κ2 E,O-EC{O}Ph2]2-. In contrast, when K[Al(NONDipp)(E)] (E = S, Se) was reacted with benzaldehyde, two equivalents of substrate were incorporated into the product accompanied by formation of a second C-E bond and complete cleavage of the Al-E{16} bonds. The products contained the hitherto unknown κ2 O,O-thio- and κ2 O,O-seleno-bis(phenylmethanolate) ligands, which were exclusively isolated as the cis-stereoisomers. The mechanisms of these cycloaddition reactions were investigated using DFT methods.

Isolation of Cyclic Aluminium Polysulfides by Stepwise Sulfurization

Despite the notable progress in aluminium chalcogenides, their sulfur congeners have rarely been isolated under mild conditions owing to limited synthetic precursors and methods. Herein, facile isolation of diverse molecular aluminium sulfides is achievable, by the reaction of N‐heterocyclic carbene‐stabilized terphenyl dihydridoaluminium (1) with various thiation reagents. Different to the known dihydridoaluminium 1^Tipp, 1 features balanced stability and reactivity at the Al center. It is this balance that enables the first monomeric aluminium hydride hydrogensulfide 2, the six‐membered cyclic aluminium polysulfide 4 and the five‐membered cyclic aluminium polysulfide 6 to be isolated, by reaction with various equivalents of elemental sulfur. Moreover, a rare aluminium heterocyclic sulfide with Al−S−P five‐membered ring (7) was obtained in a controlled manner. All new compounds were fully characterized by multinuclear NMR spectroscopy and elemental analysis. Their structures were confirmed by single‐crystal X‐ray diffraction studies.

Strained and Reactive Donor/Acceptor-Supported Metallasilanone

A novel stable donor/acceptor-supported Mn^I -metallasilanone 3 was synthesized. The intramolecular silanone-Mn^I interaction induces a highly strained three-membered cyclic structure, leading to an exceptionally high reactivity of 3 as a donor/acceptor complex of silanone. Indeed, metallasilanone 3 readily reacts with various small molecules such as H₂ or ethylene gas in mild conditions.

Mechanistic Insights into Activation of Carbon Monoxide, Carbon Dioxide, and Nitrous Oxide by Acyclic Silylene

Owing to an empty p orbital and a lone pair of electrons on the Si center, silylene exhibits reactivity similar to a transition-metal system capable of activating H₂/C-H bonds and small molecules. In this work, with the aid of density functional theory calculations, we systematically investigated the reactions of an acyclic silylene with CO, CO₂, and N₂O. The detailed mechanisms obtained lead to an in-depth understanding of the silylene single-site ambiphilic reactivity.

Acid-Base Free Main Group Carbonyl Analogues

Main group carbonyl analogues (R2 E=O) derived from p-block elements (E=groups 13 to 15) have long been considered as elusive species. Previously, employment of chemical tricks such as acid- and base-stabilization protocols granted access to these transient species in their masked forms. However, electronic and steric effects inevitably perturb their chemical reactivity and distinguish them from classical carbonyl compounds. A new era was marked by the recent isolation of acid-base free main group carbonyl analogues, ranging from a lighter boracarbonyl to the heavier silacarbonyls, phosphacarbonyls and a germacarbonyl. Most importantly, their unperturbed nature elicits exciting new chemistry, spanning the vista from classical organic carbonyl-type reactions to transition metal-like oxide ion transfer chemistry. In this Review, we survey the strategies used for the isolation of such systems and document their emerging reactivity profiles, with a view to providing fundamental comparisons both with carbon and transition metal oxo species. This highlights the emerging opportunities for exciting "crossover" reactivity offered by these derivatives of the p-block elements.

Main Group Multiple Bonds for Bond Activations and Catalysis

Since the discovery that the so-called "double-bond" rule could be broken, the field of molecular main group multiple bonds has expanded rapidly. With the majority of homodiatomic double and triple bonds realised within the p-block, along with many heterodiatomic combinations, this Minireview examines the reactivity of these compounds with a particular emphasis on small molecule activation. Furthermore, whilst their ability to act as transition metal mimics has been explored, their catalytic behaviour is somewhat limited. This Minireview aims to highlight the potential of these complexes towards catalytic application and their role as synthons in further functionalisations making them a versatile tool for the modern synthetic chemist.

Double insertion of CO2 into an Al–Te multiple bond

Two equivalents of CO₂ react with a terminal Al–Te bond to form the tellurodicarbonate ligand.

A BH Borenium-Derived Thioxoborane, Its Persulfide, and Their Li+-Induced Reactions with Alkynes and with Carbon Dioxide

Insertion of sulfur into the B-H bond of the BH borenium salt [IMes(C₆F₅)BH]⁺ followed by deprotonation gave the thioxoborane IMes(C₆F₅)B═S. Subsequent treatment with additional sulfur gave the corresponding boron persulfide, a NHC-stabilized boradithiirane. The B═S compound reacted with carbon dioxide in the presence of the lithium salt Li[B(C₆F₅)₄] by formal [2+2] cycloaddition to give a boron thiocarbonate-type product. The boron persulfide formally inserted phenyl acetylene into the B-S bond in the presence of Li[B(C₆F₅)₄] to give the respective five-membered heterocycle.

Synthesis of a "Masked" Terminal Zinc Sulfide and Its Reactivity with Brønsted and Lewis Acids

The "masked" terminal Zn sulfide, [K(2.2.2-cryptand)][^Me LZn(S)] (2) (^Me L={(2,6-ⁱ Pr₂ C₆ H₃ )NC(Me)}₂ CH), was isolated via reaction of [^Me LZnSCPh₃ ] (1) with 2.3 equivalents of KC₈ in THF, in the presence of 2.2.2-cryptand, at -78 °C. Complex 2 reacts readily with PhCCH and N₂ O to form [K(2.2.2-cryptand)][^Me LZn(SH)(CCPh)] (4) and [K(2.2.2-cryptand)][^Me LZn(SNNO)] (5), respectively, displaying both Brønsted and Lewis basicity. In addition, the electronic structure of 2 was examined computationally and compared with the previously reported Ni congener, [K(2.2.2-cryptand)][^tBu LNi(S)] (^tBu L={(2,6-ⁱ Pr₂ C₆ H₃ )NC(^t Bu)}₂ CH).

CO scission and reductive coupling of organic carbonyls by a redox-active diboraanthracene

A gold-stabilized diboraanthracene mediates reductive transformations of carbonyls, including C–O and C–C bond formation, and deoxygenation of acetone to propene and hydroxide.

Synthesis and reactivity of a terminal aluminium–imide bond

The Al–N_imide bond in a new anionic aluminium imide complex reacts via a [2+2] cycloaddition with CO₂ to afford the dianionic carbamate ligand.

Bifurcated Hydrogen-Bond-Stabilized Boron Analogues of Carboxylic Acids

The reactivity of a bulky m-terphenylboronic acid, DmpB(OH)₂ [1; Dmp = 2,6-bis(2,4,6-trimethylphenyl)phenyl], toward three different N-heterocyclic carbenes has been examined. The reaction of 1 with 1 equiv of bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) leads to the formation of a hydrogen-bonded carbene boronic acid adduct, 2, featuring strong O-H···C contacts. In contrast, more basic 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (IPr₂Me₂) and 1,3-di-tert-butylimidazol-2-ylidene (I^tBu) deprotonate 1 smoothly to afford the rare anionic boranuidacarboxylic acids 3 and 4, respectively. Structural determination reveals that 3 and 4 bear unprecedented bifurcated hydrogen bonds with a BO^- unit as a double hydrogen-bond acceptor, which contribute significantly to stabilization of the highly reactive B═O double bond. Quantum-mechanical calculations were conducted to disclose the unique electronic properties of the multiple bonds, as well as the important hydrogen bonds in these compounds.

Heterodiatomic Multiple Bonding in Group 13: A Complex with a Boron-Aluminum π Bond Reduces CO2

Heterodiatomic multiple bonds have never been observed within Group 13. Herein, we disclose a method that generates [(CAAC)PhB=AlCp^3t ] (1), a complex featuring π bonding between boron and aluminum through the association of singlet fragments. We present the properties of this multiple bond as well as the reactivity of the complex with carbon dioxide, which yields a boron CO complex via an unusual metathesis reaction.

An Acid-Free Anionic Oxoborane Isoelectronic with Carbonyl: Facile Access and Transfer of a Terminal B═O Double Bond

We disclose the synthesis and structural characterization of the first acid-free anionic oxoborane, [K(2.2.2-crypt)][(HCDippN)₂BO] (1) (Dipp = 2,6- ⁱPr₂C₆H₃), which is isoelectronic with classical carbonyl compounds. 1 can readily be accessed from its borinic acid by a simple deprotonation/sequestration sequence. Crystallographic and density functional theory (DFT) analyses support the presence of a polarized terminal B═O double bond. Subsequent π bond metathesis converts the B═O bond to a heavier B═S containing system, affording the first anionic thioxoborane [K(2.2.2-crypt)][(HCDippN)₂BS] (2), isoelectronic with thiocarbonyls. Facile B═O bond cleavage can also be achieved to access B-H and B-Cl bonds and, via a remarkable oxide (O^2-) ion abstraction, to generate a borenium cation [(HCDippN)₂B(NC₅H₅)][OTf] (4). By extension, 1 can act as an oxide transfer agent to organic substrates, a synthetic role traditionally associated with transition-metal compounds. Hence we show that B-O linkages, which are often considered to be thermodynamic sinks, can be activated under mild conditions toward bond cleavage and transfer, by exploiting the higher reactivity inherent in the B═O double bond.

An N-Heterocyclic Boryloxy Ligand Isoelectronic with N-Heterocyclic Imines: Access to an Acyclic Dioxysilylene and its Heavier Congeners

Introduced here is a new type of strongly donating N-heterocyclic boryloxy (NHBO) ligand, [(HCDippN)₂ BO]^- (Dipp=2,6-diisopropylphenyl), which is isoelectronic with the well-known N-heterocyclic iminato (NHI) donor class. This 1,3,2-diazaborole functionalized oxy ligand has been used to stabilize the first acyclic two-coordinate dioxysilylene and its Ge, Sn, and Pb congeners, thereby presenting the first complete series of heavier group 14 dioxycarbene analogues. All four compounds have been characterized by X-ray crystallography and density-functional theory, enabling analysis of periodic trends: the potential for the [(HCDippN)₂ BO]^- ligand to subtly vary its electronic-donor capabilities is revealed by snapshots showing the gradual evolution of arene π coordination on going from Si to Pb.

BeBe triple bond in Be2X4Y2 clusters (X = Li, Na and Y = Li, Na, K) and a perfect classical BeBe triple bond presented in Be2Na4K2

The trans-bent Be₂X₄Y₂ structures are explained through ESP of Be₂X₄ and a perfect BeBe triple bond is confirmed in D_4h-Be₂Na₄K₂.

Cationic Complexes of Boron and Aluminum: An Early 21st Century Viewpoint

Boron and aluminum are lighter Group 13 elements, found in daily life commodities, and considered environmentally benign. Nevertheless, they markedly differ in their elemental properties (e.g., metal character, atomic radius). The use of Lewis acidic complexes of boron and aluminum for methods of bond activation and catalysis (e.g., hydrogenation of unsaturated substrates, polymerization of olefins and epoxides) is quickly expanding. The introduction of cationic charge may boost the metalloid-centered Lewis acidity and allow for its fine-tuning particularly with regard to preference for "hard" or "soft" Lewis bases (i.e., substrates). Especially the isolation of low-coordinate cations (number of ligand atoms smaller than four) demands elaborate techniques of thermodynamic and kinetic stabilization (i.e., electronic saturation and steric shielding) by a ligand system. Furthermore, the properties of the solvent and the counteranion must be considered with care. Here, selected examples of boron and aluminum cations are described.

M-S Multiple Bond in HMSH, H2MS, and HMS Molecules (M = B, Al, Ga): Matrix Infrared Spectra and Theoretical Calculations

Reaction products of B, Al, and Ga atoms with H₂S have been identified in solid argon using matrix isolation infrared absorption spectroscopy. The results show that the ground state B atom reaction with H₂S gives the H₂BS molecule while for the Al atom the HAlSH molecule forms first, which then further isomerizes to H₂AlS upon >500 nm irradiation. The reaction of the Ga atom with H₂S only takes place upon photolysis to produce HGaSH in the matrix. The assignments of the major modes for these products were confirmed by appropriate ¹⁰B, ¹¹B, D₂S, and H₂³⁴S isotopic shifts and theoretical frequency calculations. Topological analysis of the electron density suggests that both HBSH and H₂BS molecules possess covalent B-S bond with significant double bond character, while the M-S bond in the heavier group 13 homologues (Al, Ga) was characterized as a polar covalent strong interaction.

NHCs in Main Group Chemistry

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

Recurrent supramolecular motifs in discrete complexes and coordination polymers based on mercury halides: prevalence of chelate ring stacking and substituent effects

We report the synthesis, X-ray characterization and DFT study of five Hg(ii) complexes with Schiff bases containing a nicotinohydrazide core to explore the formation of chelate-ring π-stacking interactions.

Synthesis of a cyclopentadienyl(imino)stannylene and its direct conversion into halo(imino)stannylenes

We report the synthesis and structure of a dimeric Cp-substituted iminostannylene as well as its unusual reactivity towards haloalkanes, resulting in the formation of halogen-substituted iminostannylenes.