Aluminium‐Mediated Carbon Dioxide Reduction by an Isolated Monoalumoxane Anion

The deoxygenative conversion of carbon dioxide to carbon monoxide is promoted by the aluminyl anion [Al(NON^Ar)]^? (NON^Ar=[O(SiMe₂NAr)₂]^2?, Ar=2,6‐iPr₂C₆H₃). The reaction proceeds via the isolable monoalumoxane anion [Al(NON^Ar)(O)]^?, containing a terminal aluminum‐oxygen bond. This species reacts with a second equivalent of carbon dioxide to afford the carbonate [Al(NON^Ar)(CO₃)]^?, and with nitrous oxide to generate the hyponitrite anion, [Al(NON^Ar)(κ²O,O′‐N₂O₂)]^?.     

Reduction vs. Addition: The Reaction of an Aluminyl Anion with 1,3,5,7‐Cyclooctatetraene

The potassium aluminyl complex K[Al(NON^Ar)] (NON=NON^Ar=[O(SiMe₂NAr)₂]^2?, Ar=2,6‐iPr₂C₆H₃) reacts with 1,3,5,7‐cyclooctatetraene (COT) to give K[Al(NON^Ar)(COT)]. The COT‐ligand is present in the asymmetric unit as a planar μ₂‐η²:η⁸‐bridge between Al and K, with additional K???π‐aryl interactions to neighboring molecules that generate a helical chain. DFT calculations indicate significant aromatic character, consistent with reduction to [COT]^2?. Addition of 18‐crown‐6 causes a rearrangement of the C₈‐carbocycle to form the isomeric 9‐aluminabicyclo[4.2.1]nona‐2,4,7‐triene anion.     

Isoelectronic Aluminium Analogues of Carbonyl and Dioxirane Moieties

We report the anion [Al(NON^Ar)(Se)]^? (NON^Ar=[O(SiMe₂NAr)₂]^2?, Ar=2,6‐iPr₂C₆H₃), which is an isoelectronic Group 13 metal analogue of the carbonyl group containing an aluminium–selenium multiple bond. It was synthesized in a single step from the reaction of the aluminyl anion [Al(NON^Ar)]^? with elemental selenium. Spectroscopic, crystallographic, and computational analysis confirmed multiple bonding between aluminium and selenium. Addition of a second equivalent of selenium afforded the diselenirane, [Al(NON^Ar)(κ²‐Se₂)]^?, which is an isoelectronic analogue of the dioxirane group.     

Bi−P Bond Homolysis as a Route to Reduced Bismuth Compounds and Reversible Activation of P4

Bismuth diphenylphosphanides Bi(NON^R)(PPh₂) (NON^R=[O(SiMe₂NR)₂], R=tBu, 2,6‐iPr₂C₆H₃, Aryl) undergo facile decomposition via single‐electron processes to form reduced Bi and P species. The corresponding derivatives Bi(NON^R)(PCy₂) are stable. Reaction of the isolated Bi^II radical ^.Bi(NON^Ar) with white phosphorus (P₄) proceeds with the reversible and selective activation of a single P?P bond to afford the bimetallic μ,η^1:1‐bicyclo[1.1.0]tetraphosphabutane compound.     

Reactivity of Liquid Ammonia Solutions of the Zintl Phase K12Sn17 towards Mesitylcopper(I) and Phosphinegold(I) Chloride

To gain more insight into the reactivity of intermetalloid clusters, the reactivity of the Zintl phase K₁₂Sn₁₇, which contains [Sn₄]^4? and [Sn₉]^4? cluster anions, was investigated. The reaction of K₁₂Sn₁₇ with gold(I) phosphine chloride yielded K₇[(η²‐Sn₄)Au(η²‐Sn₄)](NH₃)₁₆ ( 1 ) and K₁₇[(η²‐Sn₄)Au(η²‐Sn₄)]₂(NH₂)₃(NH₃)₅₂ ( 2 ), which both contain the anion [(Sn₄)Au(Sn₄)]^7? ( 1 a ) that consists of two [Sn₄]^4? tetrahedra linked through a central gold atom. Anion 1 a represents the first binary Au?Sn polyanion. From this reaction, the solvate structure [K([2.2.2]crypt)]₃K[Sn₉](NH₃)₁₈ ( 3 ; [2.2.2]crypt=4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) was also obtained. In the analogous reaction of mesitylcopper with K₁₂Sn₁₇ in the presence of [18]crown‐6 in liquid ammonia, crystals of the composition [K([18]crown‐6)]₂[K([18]crown‐6)(MesH)(NH₃)][Cu@Sn₉](thf) ( 4 ) were isolated ([18]crown‐6=1,4,7,10,13,16‐hexaoxacyclooctadiene, MesH=mesitylene, thf=tetrahydrofuran) and featured a [Cu@Sn₉]^3? cluster. A similar reaction with [2.2.2]crypt as a sequestering agent led to the formation of crystals of [K[2.2.2]crypt][MesCuMes] ( 5 ). The cocrystallization of mesitylene in 4 and the presence of [MesCuMes]^? ( 5 a ) in 5 provides strong evidence that the migration of a bare Cu atom into an Sn₉ anion takes place through the release of a Mes^? anion from mesitylcopper, which either migrates to another mesitylcopper to form 5 a or is subsequently protonated to give MesH.     

Carbon–Carbon Bond Forming Reactions Promoted by Aluminyl and Alumoxane Anions: Introducing the Ethenetetraolate Ligand

[K{Al(NON^Dipp)}]₂ (NON^Dipp=[O(SiMe₂NDipp)₂]^2?, Dipp=2,6‐iPr₂C₆H₃) reacts with CS₂ to afford the trithiocarbonate species [K(OEt₂)][Al(NON^Dipp)(CS₃)] 1 or the ethenetetrathiolate complex, [K{Al(NON^Dipp)(S₂C)}]₂ [ 3 ]₂. The dimeric alumoxane [K{Al(NON^Dipp)(O)}]₂ reacts with carbon monoxide to afford the oxygen analogue of 3 , [K{Al(NON^Dipp)(O₂C)}]₂ [ 4 ]₂ containing the hitherto unknown ethenetetraolate ligand, [C₂O₄]^4?.     

Structure and Bonding in [Sb@In8Sb12]3− and [Sb@In8Sb12]5−

We report the characterization of the compound [K([2.2.2]crypt)]₄[In₈Sb₁₃], which proves to contain a 1:1 mixture of [Sb@In₈Sb₁₂]^3? and [Sb@In₈Sb₁₂]^5?. The tri‐anion displays perfect T_h symmetry, the first completely inorganic molecule to do so, and contains eight equivalent In³⁺ centers in a cube. The gas‐phase potential energy surface of the penta‐anion has eight equivalent minima where the extra pair of electrons is localized on one In⁺ center, and these minima are linked by low‐lying transition states where the electron pair is delocalized over two adjacent centers. The best fit to the electron density is obtained from a model where the structure of the 5? cluster lies close to the gas‐phase transition state.     

[Bi4]6– – The Zintl Anion with the Highest Charge per Atom Obtained from Solution

From the dark‐purple solution of the Zintl phase KBi in liquid ammonia dark‐blue crystals of the ammonia solvate K₆[Bi₄](NH₃)₈ were obtained. In contrast to known Bi_n polyanions the chemical bond in the anion [Bi₄]^6– is in accordance with the (8‐N) rule featuring solely Bi–Bi single bonds. [Bi₄]^6– is a butane‐analog valence compound, and with 6 negative charges per 4 atoms it is the anion with the highest known charge per atom obtained from solution. The planarity of the trans‐[Bi₄]^6– unit hints at π orbital contributions of the bismuth atoms. The corresponding reactions of the phases K₅Bi₄ and K₃Bi₂ in liquid ammonia in the presence of [2.2.2]crypt(4, 7, 13, 16, 21, 24‐hexaoxa‐1, 10‐diazabicyclo‐[8.8.8]hexacosane) lead to the salt [K([2.2.2]crypt)]₂[Bi₂](NH₃)₄ with the known electron‐deficient [Bi₂]^2– polyanion and a Bi=Bi double bond.     

Ligand Effects on the Electronic Structure of Heteroleptic Antimony‐Centered Radicals

We report on the structures of three unprecedented heteroleptic Sb‐centered radicals [L(Cl)Ga](R)Sb^. ( 2‐R , R=B[N(Dip)CH]₂ 2‐B , 2,6‐Mes₂C₆H₃ 2‐C , N(SiMe₃)Dip 2‐N ) stabilized by one electropositive metal fragment [L(Cl)Ga] (L=HC[C(Me)N(Dip)]₂, Dip=2,6‐i‐Pr₂C₆H₃) and one bulky B‐ ( 2‐B ), C‐ ( 2‐C ), or N‐based ( 2‐N ) substituent. Compounds 2‐R are predominantly metal‐centered radicals. Their electronic properties are largely influenced by the electronic nature of the ligands R, and significant delocalization of unpaired‐spin density onto the ligands was observed in 2‐B and 2‐N . Cyclic voltammetry (CV) studies showed that 2‐B undergoes a quasi‐reversible one‐electron reduction, which was confirmed by the synthesis of [K([2.2.2]crypt)][L(Cl)GaSbB[N(Dip)CH]₂] ([K([2.2.2]crypt)][ 2‐B ]) containing the stibanyl anion [ 2‐B ]^?, which was shown to possess significant Sb?B multiple‐bonding character.     

Carbon–Carbon Bond Forming Reactions Promoted by Aluminyl and Alumoxane Anions: Introducing the Ethenetetraolate Ligand

[K{Al(NON^Dipp)}]₂ (NON^Dipp=[O(SiMe₂NDipp)₂]²⁻, Dipp=2,6-iPr₂C₆H₃) reacts with CS₂ to afford the trithiocarbonate species [K(OEt₂)][Al(NON^Dipp)(CS₃)] 1 or the ethenetetrathiolate complex, [K{Al(NON^Dipp)(S₂C)}]₂ [ 3 ]₂. The dimeric alumoxane [K{Al(NON^Dipp)(O)}]₂ reacts with carbon monoxide to afford the oxygen analogue of 3 , [K{Al(NON^Dipp)(O₂C)}]₂ [ 4 ]₂ containing the hitherto unknown ethenetetraolate ligand, [C₂O₄]⁴⁻.     

On the Formation of Intermetalloid Clusters: Titanocene(III)diammin as a Versatile Reactant Toward Nonastannide Zintl Clusters

The reactivity of TiCp₂Cl₂ (d⁰) towards Zintl clusters was studied in liquid ammonia (Cp=cyclopentadienyl). Reduction of Ti^IVCp₂Cl₂ and ligand exchange led to the formation of [Ti^IIICp₂(NH₃)₂]⁺, also obtainable by recrystallization of [CpTi^IIICl]₂. Upon reaction with [K₄Sn₉], ligand exchange leads to [TiCp₂(η¹‐Sn₉)(NH₃)]^3?. A small variation of the stoichiometry led to the formation of [Ti(η⁴‐Sn₈)Cp]^3?, which cocrystallizes with [TiCp₂(NH₃)₂]⁺ and [TiCp₂(η¹‐Sn₉)(NH₃)]^3?. Finally, the large intermetalloid cluster anion [Ti₄Sn₁₅Cp₅]^n? (n=4 or 5) was obtained from the reaction of K₁₂Sn₁₇ and TiCp₂Cl₂ in liquid ammonia. The isolation of three side products, [K([18]crown‐6)]Cp, [K([18]crown‐6)]Cp(NH₃), and [K([2.2]crypt)]Cp, suggests a stepwise elimination of the Cl^? and Cp^? ligands from TiCp₂Cl₂ and thus gives a hint to the mechanism of the product formation in which [Ti(η⁴⁺²‐Sn₈)Cp]^3? has a key role.     

Ionic‐Radius‐Driven Selection of the Main‐Group‐Metal Cage for Intermetalloid Clusters [Ln@PbxBi14−x]q− and [Ln@PbyBi13−y]q− (x/q=7/4, 6/3; y/q=4/4, 3/3)

Reactions of the binary, pseudo‐homoatomic Zintl anion (Pb₂Bi₂)^2? with Ln(C₅Me₄H)₃ (Ln=La, Ce, Nd, Gd, Sm, Tb) in the presence of [2.2.2]crypt in ethane‐1,2‐diamine/toluene yielded ten [K([2.2.2]crypt)]⁺ salts of lanthanide‐doped semimetal clusters with 13 or 14 surface atoms. Single‐crystal X‐ray diffraction and energy‐dispersive X‐ray spectroscopy indicated the presence of the anions [Ln@Pb₆Bi₈]^3?, [Ln@Pb₃Bi₁₀]^3?, [Ln@Pb₇Bi₇]^4?, or [Ln@Pb₄Bi₉]^4? in single or double salts; the latter showed various ratios of the components in the solid state. The anions are the first ternary intermetalloid clusters comprising only elements of the sixth period of the periodic table, namely, Pb, Bi and lanthanides. This study, which was complemented by ESI mass spectrometry and ¹³⁹La NMR spectroscopy in solution, rationalizes a continuous development of the ratio of 13:14‐atom cages with the ionic radius of the embedded Ln³⁺ ion, which seems to select the most suitable cage type. Quantum chemical investigations helped to analyze this situation in more detail and to explain the observed subtle influence of the atomic radii. Magnetic measurements confirmed that the embedded Ln³⁺ ions keep their expected paramagnetic or diamagnetic nature.     

Extraction of Ternary Alloys: Synthesis and Crystal Structure of [K([2.2.2]crypt)]Cs7[Sn9]2(en)3

The compound [K([2.2.2]crypt)]Cs₇[Sn₉]₂(en)₃ ( 1 ) was synthesized from an alloy of formal composition KCs₂Sn₉ by dissolving in ethylenediamine (en) followed by the addition of [2.2.2]crypt and toluene. 1 crystallizes in the orthorhombic space group Pcca with a = 45.38(2), b = 9.092(4), c = 18.459(8) Å, and Z = 4. The structure consists of Cs₇[Sn₉]₂ layers which contain [Sn₉]^4– anions and Cs⁺ cations. The layers are separated by [K([2.2.2]crypt)]⁺ units. In the intermetallic slab (Cs₇[Sn₉]₂)^– compares the arrangement of pairs of symmetry‐related [Sn₉]^4– anions with the dimer ([Ge₉]–[Ge₉])^6– in [K([2.2.2]crypt)]₂Cs₄([Ge₉]–[Ge₉]), in which the clusters are linked by a cluster‐exo bond. The shortest distance between atoms of such two clusters in 1 is 4.762 Å, e. g. there are no exo Sn‐Sn bonds. The [Sn₉]^4– anion has almost perfect C_4v‐symmetry.     

The Neat Ternary Solid K5−xCo1−xSn9 with Endohedral [Co@Sn9]5− Cluster Units: A Precursor for Soluble Intermetalloid [Co2@Sn17]5− Clusters

A new type of Zintl phase is presented that contains endohedrally filled clusters and that allows for the formation of intermetalloid clusters in solution by a one‐step synthesis. The intermetallic compound K_5?xCo_1?xSn₉ was obtained by the reaction of a preformed Co? Sn alloy with potassium and tin at high temperatures. The diamagnetic saltlike ternary phase contains discrete [Co@Sn₉]^5? clusters that are separated by K⁺ ions. The intermetallic compound K_5?xCo_1?xSn₉ readily and incongruently dissolves in ethylenediamine and in the presence of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (2.2.2‐crypt), thereby leading to the formation of crystalline [K([2.2.2]crypt)]₅[Co₂Sn₁₇]. The novel polyanion [Co₂Sn₁₇]^5? contains two Co‐filled Sn₉ clusters that share one vertex. Both compounds were characterized by single‐crystal X‐ray structure analysis. The diamagnetism of K_5?xCo_1?xSn₉ and the paramagnetism of [K([2.2.2]crypt)]₅[Co₂Sn₁₇] have been confirmed by superconducting quantum interference device (SQUID) and EPR measurements, respectively. Quantum chemical calculations reveal an endohedral Co^1? atom in an [Sn₉]^4? nido cluster for [Co@Sn₉]^5? and confirm the stability of the paramagnetic [Co₂Sn₁₇]^5? unit.     

pH-Dependent Syntheses,Crystal Structures and Properties of Three Low-Dimensional Iodoargentate Hybrids

By simply changing pH value of reaction solution, three low-dimensional iodoargentate hybrids, [HDABCO]₂[(DABCO)₂(Ag₂I₄)] (1), [HDABCO]_0.5[(HDABCO)_0.5(AgI₂)] (2) and [(Me₂NH₂)(H₂DABCO)][AgI₄] (3) (DABCO = 1,4-diazabicyclo-[2.2.2]octane), have been synthesized. Noteworthy, variation in protonated degree and aggregating forms of DABCO at different pH value, the structure of inorganic moieties vary regularly from 0D [(DABCO)₂(Ag₂I₄)]^2? anion for 1 to 1D [(HDABCO)_0.5(AgI₂)]^0.5? chain for 2 and 0D [AgI₄]^3? anion for 3, exhibiting unique structural directing effects. In addition, three compounds display structure-dependent semiconductor natures and thermal stabilities.     

Synthesis and reactivity of neodymium(III) amido-tethered N-heterocyclic carbene complexes

The reaction of the heteroleptic Nd(III) iodide, [Nd(L′)(N″)(μ-I)] with the potassium salts of primary aryl amides [KN(H)Ar′] or [KN(H)Ar^*] affords heteroleptic, structurally characterised, low-coordinate neodymium amides [Nd(L′)(N″)(N(H)Ar′)] and [Nd(L′)(N″)(N(H)Ar^*)] cleanly (L′ = t-BuNCH₂CH₂[C{NC(SiMe₃)CHNt-Bu}], N″ = N(SiMe₃)₂, Ar′ = 2,6-Dipp₂C₆H₃, Dipp = 2,6-Prⁱ₂C₆H₃, Ar^* = 2,6-(2,4,6-Prⁱ₃C₆H₂)₂C₆H₃). The potassium terphenyl primary amide [KN(H)Ar^*] is readily prepared and isolated, and structurally characterised. Treatment of these primary amide-containing compounds with alkali metal alkyl salts results in ligand exchange to give alkali metal primary amides and intractable heteroleptic Nd(III) alkyl compounds of the form [Nd(L′)(N″)(R)] (R = CH₂SiMe₃, Me). Attempted deprotonation of the Nd-bound primary amide in [Nd(L′)(N″)(N(H)Ar^*)] with the less nucleophilic phosphazene superbase Bu^tNP{NP(NMe₂)₃}₃ resulted in indiscriminate deprotonations of peripheral ligand CH groups.     

Isolation and Characterization of a Bismuth(II) Radical

More than 80 years after Paneth’s report of dimethyl bismuth, the first monomeric Bi^II radical that is stable in the solid state has been isolated and characterized. Reduction of the diamidobismuth(III) chloride Bi(NON^Ar)Cl (NON^Ar=[O(SiMe₂NAr)₂]²⁻; Ar=2,6‐iPr₂C₆H₃) with magnesium affords the Bi^II radical ^.Bi(NON^Ar). X‐ray crystallographic measurements are consistent with a two‐coordinate bismuth in the +2 oxidation state with no short intermolecular contacts, and solid‐state SQUID magnetic measurements indicate a paramagnetic compound with a single unpaired electron. EPR and density functional calculations show a metal‐centered radical with >90 % spin density in a p‐type orbital on bismuth.     

Formation of [Bi11]3−, A Homoatomic,Polycyclic Bismuth Polyanion,by Pyridine‐Assisted Decomposition of [GaBi3]2−

Until now, polycyclic bismuth polyanions have not been known—thus discriminating bismuth from its lighter congeners. However, the synthesis of [K([2.2.2]crypt)]₃(Bi₁₁)?2 py?tol, allows us to present the first structurally characterized homoatomic, polycyclic bismuth polyanion, which exhibits the [P₁₁]^3? “ufosan” structure. It was obtained upon treatment of [K([2.2.2]crypt)]₂(GaBi₃)?en with the solvent pyridine. The binary Zintl anion [GaBi₃]^2? decomposes under oxidative coupling of pyridine molecules and release of H₂ to form the title compound. The unprecedented reaction, its products and by‐products were investigated by means of spectroscopy, spectrometry, and DFT studies. All findings reveal the specific reaction conditions to be crucial for the formation of the [Bi₁₁]^3? ion—and indicate the possibility of the generation and isolation of further, large bismuth polyanions.     

Synthesis and Characterization of Cationic Low‐Valent Gallium Complexes of Cryptand[2.2.2]

The synthesis and characterization of two bimetallic, cationic low‐valent gallium–cryptand[2.2.2] complexes is reported. The reaction of cryptand[2.2.2] with Ga₂Cl₄ gave two different cations, [Ga₃Cl₄(crypt‐222)]⁺ ( 1 ) or [Ga₂Cl₂(crypt‐222)]²⁺ ( 2 ), depending on whether or not trimethylsilyl triflate (Me₃SiOTf) was added as a co‐reagent. Complexes 1 and 2 are the first examples of bimetallic cryptand[2.2.2] complexes, as well as the first low‐valent gallium–cryptand[2.2.2] complexes. Computational methods were used to evaluate the bonding in the gallium cores.     

Distibanes and Distibenes from Reduction of Sb(NONR)Cl by using MgI Reagents

The bis(amidodimethyl)disiloxane antimony chlorides Sb(NON^R)Cl (NON^R=[O(SiMe₂NR)₂]²⁻; R=tBu, Ph, 2,6-Me₂C₆H₃=Dmp, 2,6-iPr₂C₆H₃=Dipp, 2,6-(CHPh₂)₂-4-tBuC₆H₂=tBu-Bhp) are reduced to Sb^II and Sb^I species by using Mg^I reagents, [Mg(BDI^R′)]₂ (BDI=[HC{C(Me)NR′}₂]⁻; R′=2,4,6-Me₃C₆H₂=Mes, Dipp). Stoichiometric reactions with Sb(NON^R)Cl (R=tBu, Ph) form dimeric Sb^II stibanes [Sb(NON^R)]₂, shown crystallographically to contain Sb−Sb single bonds. The analogous distibane with R=Dmp substituents has an exceptionally long Sb−Sb interaction and exhibits spectroscopic and reactivity properties consistent with radical character in solution. When R=Dipp, reductions with Mg^I reagents directly give distibenes [Sb(μ-NON^Dipp)Mg(BDI^R′)(THF)_n]₂ (R′=Mes, n=1; R′=Dipp, n=0). Crystallographic analysis shows a trans-substitution of the Sb=Sb double bond, with bridging NON^Dipp-ligands between the Sb^I and Mg^II centres. An attempt to access the NON^Ph-analogue using the same protocol afforded the polystibide cluster Sb₈[μ₄,η^2:2:2:2-Mg(BDI^Mes)]₄, which co-crystallized with the ligand transfer product, [Mg(BDI^Mes)]₂(μ-NON^Ph).