Site-Selective CO2 Reduction over Highly Dispersed Ru-SnOx Sites Derived from a [Ru@Sn9]6– Zintl Cluster

Converting CO2 Into Natural Gas Within the Autoclave: A Kinetic Study on Hydrogenation of Carbonates in Aqueous Solution

Catalytic conversion of carbon dioxide (CO2) into value-added chemicals is of pivotal importance, well the cost of capturing CO2 from dilute atmosphere is super challenge. One promising strategy is combining the adsorption and transformation at one step, such as applying alkali solution that could selectively reduce carbonate (CO3 2-) as consequences of CO2 adsorption. Due to complexity of this system, the mechanistic details on controlling the hydrogenation have not been investigated in depth. Herein, Ru/TiO2 catalyst was applied as a probe to elucidate the mechanism of CO3 2- activation, in which with thermodynamic and kinetic investigations, a compact Langmuir-Hinshelwood reaction model was established which suggests that the overall rate of CO3 2- hydrogenation was controlled by a specific C-O bond rupture elementary step within HCOO- and the Ru surface was mainly covered by CO3 2- or HCOO- at independent conditions. This assumption was further supported by negligible kinetic isotope effects (kH/kD≈1), similarity on reaction barriers of CO3 2- and HCOO- hydrogenation (ΔH≠ hydr,Na2CO3 and ΔH≠ hydr,HCOONa) and a non-variation of entropy (ΔS≠ hydr≈0). More interestingly, the alkalinity of the solution is certainly like a two sides in a sword and could facilitate the adsorption of CO2 while hold back catalysis during CO3 2- hydrogenation.

Transforming carbon dioxide into a methanol surrogate using modular transition metal-free Zintl ions

Although not the only greenhouse gas, CO2 is the poster child. Unsurprisingly, therefore, there is global interest across industrial and academic research in its removal and subsequent valorisation, including to methanol and its surrogates. Although difficult to study, the heterogenous pnictogens represent one important category of catalytic materials for these conversions; their high crustal abundance and low cost offers advantages in terms of sustainability. Here, Zintl clusters based on these elements are studied as homogenous atom-precise models in CO2 reduction. A family of group 13 functionalized pnictogen clusters with the general formula [(R2E)Pn7]2- (E = B, Al, In; Pn = P, As) is synthesized and their catalytic competency in the reduction of CO2 probed. Trends in both turnover numbers and frequencies are compared across this series, and [(iBu2Al)P7]2- found to be very high-performing and recyclable. Electronic structures across the series are compared using density functional theory to provide mechanistic insights.

Zintl Clusters as a Platform for Lewis Acid Catalysis

Clusters of the main group elements phosphorus and arsenic, commonly categorized as Zintl clusters, have been known for over a century. And, only now is the application of these systems as catalysts for organic synthesis being investigated. In this work, boranes are tethered via an aliphatic linker to Zintl-based clusters and their Lewis acidity is examined experimentally, by the Gutmann-Beckett test and competency in the hydroborative reduction of six organic substrates, as well as computationally, by fluoride ion affinity and hydride ion affinity methods. The effects of tuning the aliphatic linker length, substituents at the boron, and changing the cluster from a seven-atom phosphorus system to a seven-atom arsenic system on reactivity are studied.

Reactivity of Tetrel-Functionalized Heptaphosphane Clusters toward Azides

In this work, the reactivity of tetrel-functionalized phosphorus clusters toward organoazides is probed. Clusters (Me3Si)3P7 (1) and (Me3Ge)3P7 (2) were reacted with benzyl azide, phenyl azide, and 4-bromophenyl azide, and it was found that the [RN] (R = benzyl, phenyl, and 4-bromophenyl) unit from the azide inserted into the phosphorus-tetrel bonds on the cluster, accompanied by N2 elimination. Through control of the azide stoichiometry, the mono-, bis-, and tris-inserted products could be observed, consistent with these insertions proceeding in a stepwise manner. The bonding between the amine moieties and clusters was further investigated by computational chemistry, and the findings were consistent with the phosphorus cluster having undergone a formal oxidation. These insertion reactions are a convenient means of accessing Zintl clusters functionalized with exo-nitrogen-bonded moieties, which, to the best of our knowledge, were previously unknown.

Effect of La3+ on the Formation of Endohedral Zintl Clusters Featuring In/Bi Shells

Investigating the interactions of f-block metal ions with p-block polyanions in multinary cluster compounds is becoming increasingly attractive but remains a challenge in terms of both the synthetic approach and the control of the structures that are formed during the syntheses. So far, two types of reactions were dominant for the formation of corresponding clusters: the reaction of binary anions of p-block elements in 1,2-diamino-ethane (en) solutions or the reaction of organobismuth compounds with corresponding f-block metal complexes in THF. Herein, we report the synthesis of [La@In2Bi11]4- (1) and its doubly μ-Bi-bridged analogue in the doubly [K(crypt-222)]+-coordinated {[K(crypt-222)]2[La@In2Bi11](μ-Bi)2[La@In2Bi11]}4- (2) as their [K(crypt-222)]+ salts [K(crypt-222)]41 and [K(crypt-222)]42, respectively, achieved by reactions of [InMes3] and [La(C5Me4H)3] (Mes = mesityl, C5Me4H = tetramethylcyclopentadienyl) with K10Ga3Bi6.65/crypt-222 (crypt-222 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) in en. In the absence of [La(C5Me4H)3], the otherwise unchanged reactions afford the anions [Bi6(InMes)(InMes2)]3- (3) and [Mes3In-InMes3]2- (4) instead, which can be isolated as their [K(crypt-222)]+ salts [K(crypt-222)]33 and [K(crypt-222)]24·tol (tol = toluene), respectively. The {Bi6} fragment observed in anion 3 is assumed to be one of the key intermediates not only toward the formation of 1 and 2 but also on the way to more general bismuth rich compounds.

Zintl Ions and Phases Promote the Catalytic Hydrophosphination of Alkynes, Alkenes, and Imines

Although Zintl ions and phases have been known for more than a century, their application as tools to build organic molecules is underdeveloped. Here, a range of Zintl ions and phases were surveyed in the hydrophosphination of alkynes, alkenes, and imines with diphenylphosphine to afford useful organophosphine products. Further investigations with diphenylphosphine in the absence of the unsaturated organic substrates revealed the formation of the diphenylphosphide anion, allowing for the conclusion that the role of the Zintl species is as an initiator in these transformations.

A robust Zintl cluster for the catalytic reduction of pyridines, imines and nitriles

Despite p-block clusters being known for over a century, their application as catalysts to mediate organic transformations is underexplored. Here, the boron functionalized [P7] cluster [(BBN)P7]2- ([1]2-; BBN = 9-borabicyclo[3.3.1]nonane) is applied in the dearomatized reduction of pyridines, as well as the hydroboration of imines and nitriles. These transformations afford amine products, which are important precursors to pharmaceuticals, agrochemicals, and polymers. Catalyst [1]2- has high stability in these reductions: recycling nine times in quinoline hydroboration led to virtually no loss in catalyst performance. The catalyst can also be recycled between two different organic transformations, again with no loss in catalyst competency. The mechanism for pyridine reduction was probed experimentally using variable time normalization analysis, and computationally using density functional theory. This work demonstrates that Zintl clusters can mediate the reduction of nitrogen containing substrates in a transition metal-free manner.

Insight into the formation of bismuth-tungsten carbonyl clusters

Multimetallic clusters play a key role as models to doped metals, as candidates to new types of superatomic catalysts and as precursors to new multimetallic solids. Understanding formation pathways is an essential and necessary step forward in the development of cluster synthesis and research, yet remains considerably lacking owing to difficulty in identification of intermediates and the ill-defined nature of common starting materials. Here we show progress in this regard by investigating the reactivity of an intermetallic solid of nominal composition 'K₅Ga₂Bi₄' with [W(cod)(CO)₄] upon extraction with ethane-1,2-diamine (en) and 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (crypt-222). Several polybismuthide intermediates and by-products were identified along the reaction pathway, ultimately forming the new polybismuthide salt [K(crypt-222)]₃[µ:η³-Bi₃{W(CO)₃}₂]∙en∙tol. DFT calculations revealed plausible reaction schemes for the transformations taking place in the reaction mixture providing insight into the complex reactivity of 'K₅Ga₂Bi₄' on the basis of in situ generation of Bi₂^2-.

A Zintl Cluster for Transition Metal-Free Catalysis: C═O Bond Reductions

The first fully characterized boron-functionalized heptaphosphide Zintl cluster, [(BBN)P7]2- ([1]2-), is synthesized by dehydrocoupling [HP7]2-. Dehydrocoupling is a previously unprecedented reaction pathway to functionalize Zintl clusters. [Na(18-c-6)]2[1] was employed as a transition metal-free catalyst for the hydroboration of aldehydes and ketones. Moreover, the greenhouse gas carbon dioxide (CO2) was efficiently and selectively reduced to methoxyborane. This work represents the first examples of Zintl catalysis where the transformation is transition metal-free and where the cluster is noninnocent.

Missing Link in the Growth of Lead-Based Zintl Clusters: Isolation of the Dimeric Plumbaspherene [Cu4Pb22]4

We report here the structure of an endohedral plumbaspherene, [Cu₄Pb₂₂]^4–, the gold analogue of which was previously postulated to be a “missing link” in the growth of larger clusters containing three and four icosahedral subunits. The cluster contains two [Cu₂Pb₁₁]^2– subunits linked through a Cu₂Pb₄ trigonal antiprism. Density functional theory reveals that the striking ability of mixed Pb/coinage metal Zintl clusters to oligomerize and, in the case of Au, to act as a site of nucleation for additional metal atoms, is a direct consequence of their nd¹⁰(n + 1)s⁰ configuration, which generates both a low-lying (n + 1)s-based LUMO and also a high-lying Pb-centered HOMO. Cluster growth and nucleation is then driven by this amphoteric character, allowing the clusters to form donor–acceptor interactions between adjacent icosahedral units or to additional metal atoms.

Filled trivacant icosahedra as building fragments in 17-atom endohedral germanides [TM2@Ge17]n- (TM = Co, Ni)

The syntheses and the characterization of two 17-atom endohedral Ge clusters, [Co₂@Ge₁₇]^6- (1a) and [Ni₂@Ge₁₇]^4- (2a), are reported. The anions 1a and 2a, which close the gap between the known 16- and 18-atom Ge clusters, are investigated by single crystal X-ray diffraction and by quantum chemical calculations. The structures mark a new example on the pathway for cluster growth towards larger clusters with icosahedral symmetry. Furthermore, the [Co@Ge₁₀]^3- anion (3a) is obtained from liquid ammonia.

Solution-Based Group 14 Zintl Anions: New Frontiers and Discoveries

ConspectusGroup 14 Zintl anions [E_x]^q- (E = Si-Pb, x = 4, 5, 9, 10) are synthetically accessible, and their diverse chemical reactivity makes them valuable synthons in the construction of larger nanoclusters with remarkable structures, intriguing patterns of chemical bonding, and tunable physical and chemical properties. A plethora of novel cluster anions have now been isolated from the reactions of polyanionic [E_x]^q- precursors with low-valent d-/f-block metal complexes, main-group organometallics, or organics in polar aprotic solvents. The range of products includes intermetalloid clusters with transition metal atom(s) embedded in main-group element cages, organometallic Zintl anions in which [E_x]^q- acts as a ligand, intermetallic Zintl anions where [E_x]^q- is bridged by ligand-free transition metal atom(s), organo-Zintl anions where [E_x]^q- is functionalized with organic-group(s), and oligomers formed through oxidative coupling reactions. The synthesis and characterization of these unconventional complexes, where important contributions to stability come from ionic, covalent, and metal-metal bonds as well as weaker aurophilic and van der Waals interactions, extend the boundaries of coordination chemistry and solid-state chemistry. Substantial progress has been made in this field over the past two decades, but there are still many mysteries to unravel related to the cluster growth mechanism and the controllable synthesis of targeted clusters, along with the remarkable and diverse patterns of chemical bonding that present a substantial challenge to theory. In this Account, we hope to shed some light on the relationship between structure, electronic properties, and cluster growth by highlighting selected examples from our recent work on homoatomic deltahedral [E_x]^q- anions, including (1) germanium-based Zintl clusters, such as the supertetrahedral intermetallic clusters [M₆Ge₁₆]^4- (M = Zn, Cd) and the sandwich cluster {(Ge₉)₂[η⁶-Ge(PdPPh₃)₃]}^4- with a heterometallic Ge@Pd₃ interlayer; (2) tin-based intermetalloid clusters [M_x@Sn_y]^q- and the application of [Co@Sn9]^4- in bottom-up synthesis; and (3) lead clusters with precious metal cores, including the largest Zintl anion [Au₁₂Pb₄₄]^8-. In addition to their intrinsic appeal from a structural and electronic perspective, these new cluster anions also show promise as precursors for the development of new materials with applications in heterogeneous catalysis, where we have recently reported the selective reduction of CO₂.

A Neutral Heteroatomic Zintl Cluster for the Catalytic Hydrogenation of Cyclic Alkenes

We report on the synthesis of an alkane-soluble Zintl cluster, [η4-Ge9(Hyp)3]Rh(COD), that can catalytically hydrogenate cyclic alkenes such as 1,5-cyclooctadiene and cis-cyclooctene. This is the first example of a well-defined Zintl-cluster-based homogeneous catalyst.