Synthesis and catalytic application of a donor-free bismuthenium cation

Herein, we report the synthesis and catalytic application of a new N,N'-dineopentyl-1,2-phenylenediamine-based bismuthenium cation (3). 3 has been synthesized via the treatment of chlorobismuthane LBiCl [L = 1,2-C6H4{N(CH2tBu)}2] (2) with AgSbF6, and was further used as a robust catalyst for the cyanosilylation of ketones under mild reaction conditions. Experimental studies and DFT calculations were performed to understand the mechanistic pathway.

Utilizing bis(imino)dihydroacridanide pincer ligands in p-block chemistry: synthesis and catalysis of an antimony monocation salt

We present the synthesis and characterization of an Sb(III) monocation salt stabilized by a bulky bis(imino)dihydroacridanide pincer ligand. The Lewis acidity of the Sb cation is quantified using the Guttmann-Beckett method and confirmed by its reaction with 4-dimethylaminopyridine, which forms a Lewis acid-base adduct. This Sb cation exhibits catalytic activity in the cyanosilylation of arylketones. The electronic structure of the Sb cation as well as the mechanism of the catalytic transformation are explored by density functional theory computations.

Binding, Sensing, And Transporting Anions with Pnictogen Bonds: The Case of Organoantimony Lewis Acids

Motivated by the discovery of main group Lewis acids that could compete or possibly outperform the ubiquitous organoboranes, several groups, including ours, have engaged in the chemistry of Lewis acidic organoantimony compounds as new platforms for anion capture, sensing, and transport. Principal to this approach are the intrinsically elevated Lewis acidic properties of antimony, which greatly favor the addition of halide anions to this group 15 element. The introduction of organic substituents to the antimony center and its oxidation from the + III to the + V state provide for tunable Lewis acidity and a breadth of applications in supramolecular chemistry and catalysis. The performances of these antimony-based Lewis acids in the domain of anion sensing in aqueous media illustrate the favorable attributes of antimony as a central element. At the same time, recent advances in anion binding catalysis and anion transport across phospholipid membranes speak to the numerous opportunities that lie ahead in the chemistry of these unique main group compounds.

Cationic Triarylchlorostibonium Lewis Acids

Organopnictogen cations show promise as powerful, tunable main-group Lewis acid catalysts. The synthesis, solid-state structures, and reactivity of a series of weakly coordinated triarylchlorostibonium salts [Ar₃SbCl][B(C₆F₅)₄] (Ar = Ph, 3-FC₆H₄, 4-FC₆H₄, 3,5-F₂C₆H₃, 2,4,6-F₃C₆H₂) are reported. The cation in each adopts a tetrahedral coordination environment of antimony, with near complete separation from the anion. Structural, computational, and reactivity studies reveal that the Lewis acidity of [Ar₃SbCl]⁺ generally increases with increased fluorination of the Ar substituents, with a secondary quenching effect from para fluorination. [Ar₃SbCl]⁺ is reduced to Ar₃Sb in the presence of Et₃SiH, and the mechanism of this reaction has been modeled computationally. Preliminary studies demonstrate that they are useful catalysts for the dimerization of 1,1-diphenylethylene and the Friedel-Crafts alkylation of benzene.

Closed Aromatic Tubes-Capsularenes

In this study, we describe a synthetic method for incorporating arenes into closed tubes that we name capsularenes. First, we prepared vase-shaped molecular baskets 4-7. The baskets comprise a benzene base fused to three bicycle[2.2.1]heptane rings that extend into phthalimide (4), naphthalimide (6), and anthraceneimide sides (7), each carrying a dimethoxyethane acetal group. In the presence of catalytic trifluoroacetic acid (TFA), the acetals at top of 4, 6 and 7 change into aliphatic aldehydes followed by their intramolecular cyclization into 1,3,5-trioxane (¹ H NMR spectroscopy). Such ring closure is nearly a quantitative process that furnishes differently sized capsularenes 1 (0.7×0.9 nm), 8 (0.7×1.1 nm;) and 9 (0.7×1.4 nm;) characterized by X-Ray crystallography, microcrystal electron diffraction, UV/Vis, fluorescence, cyclic voltammetry, and thermogravimetry. With exceptional rigidity, unique topology, great thermal stability, and perhaps tuneable optoelectronic characteristics, capsularenes hold promise for the construction of novel organic electronic devices.

Binuclear Triphenylantimony(V) Catecholates through N-Donor Linkers: Structural Features and Redox Properties

A series of binuclear triphenylantimony(V) bis-catecholato complexes 1–11 of the type (Cat)Ph₃Sb-linker-SbPh₃(Cat) was prepared by a reaction of the corresponding mononuclear catecholates (Cat)SbPh₃ with a neutral bidentate donor linker ligands pyrazine (Pyr), 4,4′-dipyridyl (Bipy), bis-(pyridine-4-yl)-disulfide (PySSPy), and diazobicyclo[2,2,2]octane (DABCO) in a dry toluene: Cat = 3,6-di-tert-butyl-catecholate (3,6-DBCat), linker = Pyr (1); PySSPy (2); Bipy (3); DABCO (4); Cat = 3,5-di-tert-butyl-catecholate (3,5-DBCat), linker = Bipy (5); DABCO (9); Cat = 4,5-(piperazine-1,4-diyl)-3,6-di-tert-butylcatecholate (pip-3,6-DBCat), linker = Bipy (6); DABCO (10); Cat = 4,5-dichloro-3,6-di-tert-butylcatecholate (4,5-Cl₂-3,6-DBCat), linker = Bipy (7); DABCO (11); and Cat = 4,5-dimethoxy-3,6-di-tert-butylcatecholate (4,5-(MeO)₂-3,6-DBCat), linker = Bipy (8). The same reaction of (4,5-Cl₂-3,6-DBCat)SbPh₃ with DABCO in an open atmosphere results in a formation of 1D coordination polymer {[(4,5-Cl₂-3,6-DBCat)SbPh₃·H₂O]·DABCO}_n (12). Bis-catecholate complex Ph₃Sb(Cat-Spiro-Cat)SbPh₃ reacts with Bipy as 1:1 yielding a rare macrocyclic tetranuclear compound {Ph₃Sb(Cat-Spiro-Cat)SbPh₃∙(Bipy)}₂ (13). The molecular structures of 1, 3, 4, 5, 8, 10, 12, and 13 in crystal state were established by single-crystal X-ray analysis. Complexes demonstrate different types of relative spatial positions of mononuclear moieties. The nature of chemical bonds, charges distribution, and the energy of Sb...N interaction were investigated in the example of complex 5. The electrochemical behavior of the complexes depends on the coordinated N-donor ligand. The coordination of pyrazine, Bipy, and PySSPy at the antimony atom changes their mechanism of electrooxidation: instead of two successive redox stages Cat/SQ and SQ/Cat, one multielectron stage was observed. The coordination of the DABCO ligand is accompanied by a significant shift in the oxidation potentials of the catecholate ligand to the cathodic region (by 0.4 V), compared to the initial complex.

Definition of the Pnictogen Bond: A Perspective

This article proposes a definition for the term “pnictogen bond” and lists its donors, acceptors, and characteristic features. These may be invoked to identify this specific subset of the inter- and intramolecular interactions formed by elements of Group 15 which possess an electrophilic site in a molecular entity.

Electroreductive CO coupling of benzaldehyde over SACs Au-NiMn2O4 spinel synergetic composites

Electroreductive CO coupling provides a prospective strategy for biomass derivative upgrading via reducing the number of oxygen-containing functional groups and increasing their molecular weight. However, exploring superior electrocatalysts with effective reactivity and high selectivity for target products are still a challenge. In this work, single atom Au surface derived NiMn₂O₄ (SACs Au-NiMn₂O₄) spinel synergetic composites were fabricated by a versatile adsorption-deposition method and applied in electroreductive self-coupling of benzaldehyde to dibenzyl ether. The SACs Au-NiMn₂O₄ spinel synergetic composites enhanced electroreductive coupling of benzaldehyde, significantly improved the yield and selectivity of dibenzyl ether. Systematic characterizations and density functional theory calculation revealed that atomically dispersed Au occupied surface Ni²⁺ vacancies, which played a dominated role in CO coupling of benzaldehyde. Detailed calculation results showed that benzaldehyde preferred to adsorb on Ni octa-hedral sites of NiMn₂O₄ spinel synergetic structure, single atom Au surficial derivation over NiMn₂O₄ further reduced the adsorption energy (E_ads) of benzaldehyde on SACs Au-NiMn₂O₄, thus the CO coupling of benzaldehyde to dibenzyl ether was promoted. Moreover, single atom Au surficial derivation lowered the energy barrier of rate-determining step, facilitated the formation of dibenzyl ether species. Our work also paves an avenue for rational design single atom materials using spinel as support.

Silver(i)-catalyzed oxidative coupling of hydrosilanes with DMF to symmetrical and unsymmetrical disiloxanes

An alternative route to symmetrical and unsymmetrical disiloxanes, utilizing a 0.5% AgNTf2 catalyst to enable oxidative coupling of hydrosilanes with DMF as an oxygen source, is reported.

Comparing London Dispersion Pnictogen-π Interactions in Naphthyl-substituted Dipnictanes

Using a combination of NMR, X-ray diffraction and quantum chemistry, the structure-directing role of London Dispersion (LD) is demonstrated for dibismuthane Bi2Naph2 (1). 1 shows intermolecular Bi···π contacts in the...

Fluoride anion complexation and transport using a stibonium cation stabilized by an intramolecular PO → Sb pnictogen bond

We describe the synthesis of [o-Ph₂P(O)(C₆H₄)SbPh₃]⁺ ([2]⁺), an intramolecularly base-stabilized stibonium Lewis acid which was obtained by reaction of [o-Ph₂P(C₆H₄)SbPh₃]⁺ with NOBF₄. This cation reacts with fluoride anions to afford the corresponding fluorostiborane o-Ph₂P(O)(C₆H₄)SbFPh₃, the structure of which indicates a strengthening of the PO → Sb interaction. When deployed in fluoride-containing POPC unilamellar vesicles, [2]⁺ behaves as a potent fluoride anion transporter whose activity greatly exceeds that of [Ph₄Sb]⁺.

Catalytic Reductive Alcohol Etherifications with Carbonyl-Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives

Ether derivatives have myriad applications in several areas of chemical industry and academia. Hence, the development of more effective and sustainable protocols for their production is highly desired. Among the different methodologies reported for ether synthesis, catalytic reductive alcohol etherifications with carbonyl-based moieties (aldehydes/ketones and carboxylic acid derivatives) have emerged in the last years as a potential tool. These processes constitute appealing routes for the selective production of both symmetrical and asymmetrical ethers (including O-heterocycles) with an increased molecular complexity. Likewise, ester-to-ether catalytic reductions and hydrogenative alcohol etherifications with CO2 to dialkoxymethanes and other acetals, albeit in less extent, have undergone important advances, too. In this Review, an update of the recent progresses in the area of catalytic reductive alcohol etherifications using carbonyl-based compounds and CO2 have been described with a special focus on organic synthetic applications and catalyst design. Complementarily, recent progress made in catalytic acetal/ketal-to-ether or ester-to-ether reductions and other related transformations have been also summarized.

Diverse structure and reactivity of pentamethylcyclopentadienyl antimony(iii) cations

Rare examples of Sb(iii) cations which are not supported by coordinative bonds demonstrate Lewis acidic reactivity.

Triple-Pnictogen Bonding as a Tool for Supramolecular Assembly

Supramolecular assembly utilizing simultaneous formation of three pnictogen bonds around a single antimony vertex was explored via X-ray crystallography, solution NMR, and computational chemistry. An arylethynyl (AE) ligand was designed to complement the three electrophilic regions around the Sb compound. Though solution studies reveal large binding constants for individual pyridyl units with the Sb donor, the rigidity and prearrangement of the AE acceptor proved necessary to achieve simultaneous binding of three acceptors to the Sb-centered pnictogen-bond donor. Calculations and X-ray structures suggest that negative cooperativity upon sequential binding of three acceptors to a Sb center limits the utility of triple-pnictogen bonding pyridyl acceptors. These limitations can be negated, however, when positive cooperativity is designed into a complementary acceptor ligand.

Carbon monoxide insertion at a heavy p-block element: unprecedented formation of a cationic bismuth carbamoyl

The first insertion reaction of CO with a molecular complex of the heavy p-block elements is reported (principal quantum number > 4).

Major advances in the chemistry of 5th and 6th row heavy p-block element compounds have recently uncovered intriguing reactivity patterns towards small molecules such as H₂, CO₂, and ethylene. However, well-defined, homogeneous insertion reactions with carbon monoxide, one of the benchmark substrates in this field, have not been reported to date. We demonstrate here, that a cationic bismuth amide undergoes facile insertion of CO into the Bi–N bond under mild conditions. This approach grants direct access to the first cationic bismuth carbamoyl species. Its characterization by NMR, IR, and UV/vis spectroscopy, elemental analysis, single-crystal X-ray analysis, cyclic voltammetry, and DFT calculations revealed intriguing properties, such as a reversible electron transfer at the bismuth center and an absorption feature at 353 nm ascribed to a transition involving σ- and π-type orbitals of the bismuth-carbamoyl functionality. A combined experimental and theoretical approach provided insight into the mechanism of CO insertion. The substrate scope could be extended to isonitriles.

Phosphonium–stibonium and bis-stibonium cations as pnictogen-bonding catalysts for the transfer hydrogenation of quinolines

Bifunctional group 15 dications are effective transfer hydrogenation catalysts, the activity of which culminates in the case of the bis-stibonium dication [o-C₆H₄(SbMePh₂)₂]²⁺.

Digging the Sigma-Hole of Organoantimony Lewis Acids by Oxidation

The development of group 15 Lewis acids is an area of active investigation that has led to numerous advances in anion sensing and catalysis. While phosphorus has drawn considerable attention, emerging research shows that organoantimony(III) reagents may also act as potent Lewis acids. Comparison of the properties of SbPh₃ , Sb(C₆ F₅ )₃ , and SbAr^F ₃ with those of their tetrachlorocatecholate analogues SbPh₃ Cat, Sb(C₆ F₅ )₃ Cat, and SbAr^F ₃ Cat (Cat=o-O₂ C₆ Cl₄ , Ar^F =3,5-(CF₃ )₂ C₆ H₃ ) demonstrates that the Lewis acidity of electron deficient organoantimony(III) reagents can be readily enhanced by oxidation to the +V state-as verified by binding studies, organic reaction catalysis, and computational studies. The results are rationalized by explaining that oxidation of the antimony center leads to a lowering of the accepting σ* orbital and a deeper carving of the associated σ-hole.

Influence of the catalyst structure in the cycloaddition of isocyanates to oxiranes promoted by tetraarylstibonium cations

In the context of our work on electron deficient group 15 cations as Lewis acid catalysts, we have synthesized the triflate salts of a series of tetraarylstibonium cations of general formula [ArSbPh3]+ with Ar = Mes (4+), o-(dimethylamino)phenyl (5+), and o-((dimethylamino)methyl)phenyl (6+). These new cationic antimony derivatives, along with the known [Ph4Sb]+ (1+), 1-naphthyltriphenylstibonium (2+), and [(Ant)SbPh3]+ (3+), have been evaluated as catalysts for the cycloaddition of oxiranes and isocyanates under mild conditions. While all stibonium cations favor the 3,4-oxazolidinone products, the reactivities of 5+ and 6+ are hindered by the ancillary amino donor which quenches the Lewis acidity of the antimony center. A comparison of the other stibonium cations shows that 4+ is the most selective catalyst.

Coordination of a stibine oxide to a Lewis acidic stiborane at the upper rim of the biphenylene backbone

The biphenylene backbone is used to support a stibine oxide stabilized intramolecularly by a SbO → Sb(v) donor–acceptor interaction.

Adducts of Donor-Functionalized Ar3P with the Soft Lewis Acid I2: Probing Simultaneous Lewis Acidity and Basicity at Internally Solvated P(III) Centers

The enhancement of donor strength of ortho-functionalized triarylphosphanes is shown to occur via different mechanisms for O- and N-donor substituents, with internal solvation of the phosphorus center observed for N donors. Nevertheless, the steric congestion about the P center is shown to significantly oppose the increase in donor ability, leading to donation weaker than that expected. A series of mono- and bis-aryl-substituted Ar₃PI₂ adducts (Ph_3-n(o-OMe-C₆H₄)_nPI₂, Ph_3-n(o-NMe₂-C₆H₄)_nPI₂, Ph_3-n(o-CH₂NMe₂-C₆H₄)_nPI₂ (n = 1, 2)) have been synthesized via the 1:1 reaction of donor-functionalized phosphanes with diiodine. These soft Lewis acid/base adducts exhibit apparent internal solvation of the donor phosphorus by the pendant donor moieties, giving rise to five- or six-coordinate phosphorus atoms acting as both Lewis base and Lewis acid; the first neutral six-coordinate simultaneous P(III) Lewis acid and Lewis base adduct is reported. Single-crystal X-ray diffraction studies reveal unexpectedly weak donor strength for one of the phosphanes, indicating significant steric hindrance as a consequence of internal solvation. Crystallographic interrogation of the corresponding iodophosphonium salts [Ar₃PI]X (X = I₃, BAr^F) shows that the cationic complexes experience a still greater influence of the steric bulk of the donor moieties than their neutral precursors. The steric and electronic contributions to bonding have been analyzed through computational studies, determining the factors governing the basicity of these donor-functionalized phosphanes, and show that enhancement of P-centered donor strength occurs by conjugation of lone pairs through the arene rings for oxygen substituents and via internal solvation for the nitrogen donors.

Efficient carbon-supported heterogeneous molybdenum-dioxo catalyst for chemoselective reductive carbonyl coupling

Selective carbonyl coupling, high symmetric ether selectivity.

Ni(ii)–N′NN′ pincer complexes catalyzed dehydrogenation of primary alcohols to carboxylic acids and H2accompanied by alcohol etherification

Ni(L)catalyzed acceptorless dehydrogenation of alcohol/alkoxide to carboxylate with H₂liberation.

Activation of an Au-Cl Bond by a Pendent SbIII Lewis Acid: Impact on Structure and Catalytic Activity

With the objective of identifying new coordination modes of ambiphilic ligands, we have investigated the bidentate Sb/P ligands (o-(Ph₂ P)C₆ H₄ )SbCl₂ (L^Cl ) and (o-(Ph₂ P)C₆ H₄ )SbPh₂ (L^Ph ). Reaction of these ligands with (tht)AuCl affords the monoligated species L^Cl AuCl (1) and L^Ph AuCl (2), respectively, in which the antimony centers are only weakly engaged with the coordinated gold atom. Treatment of 1 with PPh₃ induces an intramolecular transfer of a chloride ligand from gold to antimony to form the zwitterionic species o-(Cl₃ Sb)C₆ H₄ (Ph₂ P)Au(PPh₃ ) (3). Natural bond orbital (NBO) calculations show that the antimony and gold centers are involved in weak Sb→Au and Au→Sb interactions, the latter reflecting the Lewis acidity of the pendent antimony group. Finally, we demonstrate that the ability of the antimony center in 1 to abstract a gold-bound chloride in the presence of a Lewis basic substrate may be utilized to activate the gold center for the electrophilic cycloisomerization of propargylic amides.