Low-Coordinate Bismuth Cations

Catalyst-controlled regiodivergence and stereodivergence in formal cross-[4+2] cycloadditions: The unique effect of bismuth(III)

The [4+2] cycloaddition is crucial for constructing six-membered rings in pharmaceuticals and natural products. Cross-[4+2] cycloadditions offer greater product diversity than traditional diene-dienophile reactions due to multiple possible pathways. However, precise control over regio- and stereoselectivity for various isomers remains a great challenge. This study reports catalyst-controlled regiodivergent formal cross-cycloadditions of acyclic dienes and enones, significantly enhancing access to diverse pyrazole-fused spirooxindoles. Chiral phosphoric acid (CPA) catalysis enables endoselective [4+2] cycloadditions, while Bi(III) with a CPA ligand yields [2+4] products with high regio- and stereoselectivity. A Claisen rearrangement of the [2+4] adduct produces the exo-selective [4+2] product, further increasing stereochemical diversity and enabling the synthesis of six regio- and stereo-isomers from a single substrate set. DFT calculations reveal that Bi(III) reverses regioselectivity by repositioning reactants in the CPA pocket and stabilizing the enone oxygen's negative charge. In addition, product 3as demonstrates therapeutic potential against triple-negative breast cancer, with an IC50 of 8.5 μM in MDA-MB-453 cells.

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.

Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements

Carbenes (R2C:), compounds with a divalent carbon atom containing only six valence shell electrons, have evolved into a broader class with the replacement of the carbene carbon or the RC moiety with main group elements, leading to the creation of main group carbene analogues. These analogues, mirroring the electronic structure of carbenes (a lone pair of electrons and an empty orbital), demonstrate unique reactivity. Over the last three decades, this area has seen substantial advancements, paralleling the innovations in carbene chemistry. Recent studies have revealed a spectrum of unique carbene analogues, such as monocoordinate aluminylenes, nitrenes, and bismuthinidenes, notable for their extraordinary properties and diverse reactivity, offering promising applications in small molecule activation. This review delves into the isolable main group carbene analogues that are in the forefront from 2010 and beyond, spanning elements from group 13 (B, Al, Ga, In, and Tl), group 14 (Si, Ge, Sn, and Pb) and group 15 (N, P, As, Sb, and Bi). Specifically, this review focuses on the potential amphiphilic species that possess both lone pairs of electrons and vacant orbitals. We detail their comprehensive synthesis and stabilization strategies, outlining the reactivity arising from their distinct structural characteristics.

Isolation and characterization of bis(silylene)-stabilized antimony(I) and bismuth(I) cations

Monovalent group 15 cations L₂Pn + (L = σ-donor ligands, Pn = N, P, As, Sb, Bi) have attracted significant experimental and theoretical interest because of their unusual electronic structures and growing synthetic potential. Herein, we describe the synthesis of a family of antimony(I) and bismuth(I) cations supported by a bis(silylene) ligand [(TBDSi₂)Pn][BAr^F₄] (TBD = 1, 8, 10, 9-triazaboradecalin; Ar^F = 3,5-CF₃-C₆H₃; Pn = Sb, (2); Bi, (3)). The structures of 2 and 3 have been unambiguously characterized spectroscopically and by X-ray diffraction analysis and DFT calculations. They feature bis-coordinated Sb and Bi atoms which exhibit two lone pairs of electrons. The reactions of 2 and 3 with methyl trifluoromethane sulfonate provide a approach for the preparation of dicationic antimony(III) and bismuth(III) methyl complexes. Compounds 2 and 3 serve as 2e donors to group 6 metals (Cr, Mo), giving rise to ionic antimony and bismuth metal carbonyl complexes 6-9.

Effects of Hypervalent Bismuth on Electronic Properties of the Azobenzene Tridentate Ligand and Roles of Lewis Acidity in Controlling Optical Properties

Organobismuth compounds have been studied in various fields, including electronic states, pnictogen bonds, and catalysis. Among them, one of the unique electronic states of the element is the hypervalent state. So far, many issues regarding the electronic structures of bismuth in hypervalent states have been revealed; meanwhile, the influence of hypervalent bismuth on the electronic properties of π-conjugated scaffolds is still vailed. Here, we synthesized the hypervalent bismuth compound, BiAz, by introducing hypervalent bismuth into the azobenzene tridentate ligand as a π-conjugated scaffold. The influence of hypervalent bismuth on the electronic properties of the ligand was evaluated from optical measurements and quantum chemical calculations. The introduction of hypervalent bismuth revealed three significant electronic effects: first, hypervalent bismuth shows position-dependent electron-donating and electron-accepting effects. Second, BiAz can have a larger effective Lewis acidity than the hypervalent tin compound derivatives reported in our previous research. Finally, the coordination of dimethyl sulfoxide transformed the electronic properties of BiAz, similar to the hypervalent tin compounds. The data from quantum chemical calculations showed that the optical properties of the π-conjugated scaffold were able to be changed by introducing hypervalent bismuth. To the best of our knowledge, we first demonstrate that the introduction of hypervalent bismuth should be a new methodology for controlling the electronic properties of π-conjugated molecules and developing sensing materials.

Kinetically Stabilized Diarylpnictogenium Ions

The newly prepared and fully characterized stibenium and bismuthenium ions [R_ind MesE]⁺ (E=Sb, Bi; R_ind =dispiro[fluorene-9,3'-(1',1',7',7'-tetramethyl-s-hydrindacen-4'-yl)-5',9''-fluorene) were rigorously compared to the previously communicated phosphenium and arsenium ions (E=P, As) as well as the bis(m-terphenyl) pnictogenium ions [(2,6-Mes₂ C₆ H₃ )₂ E]⁺ (E=Sb, Bi). It is demonstrated that the choice of the aryl substituents dramatically effects the molecular structures (e. g. the primary E-C bond lengths) and the electronic structures (e. g. the energy of the LUMOs).

Binary interpnictogen compounds bearing diaryl bismuth fragments bound to all lighter pnictogens

Multiple interpnictogen compounds with covalent single bonds between a diarylbismuth fragment and all lighter pnictogens were prepared from the corresponding diarylhalido bismuthanes. The aminobismuthanes Ph₂BiNMe₂ (1) and Mes₂BiNMe₂ (2) (Mes = 2,4,6-trimethylphenyl-) have been obtained via a salt metathesis reaction and compound 2 was successfully reacted with tBuNH₂ in a condensation reaction to yield Mes₂BiNHtBu (3). The bismuthanyl phosphanes Ar₂BiPtBu₂ (Ar = Ph: 4 and Ar = Mes: 5) and arsanes Ar₂BiAstBu₂ (Ar = Ph: 8 and Ar = Mes: 9) were also obtained via salt metathesis. Through a trimethylsilyl halide abstraction reaction of the diaryl halido bismuthanes and EtBu(SiMe₃)₂ (E = P and As), the bismuthanyl phosphanes Ar₂BiPtBu(SiMe₃) (Ar = Ph: 6; Ar = Mes: 7) and the arsanes Ar₂BiAstBu(SiMe₃) (Ar = Ph: 10; Ar = Mes: 11) have been prepared. Bismuthanyl stibanes were accessed via a condensation reaction of Mes₂SbH with 1 or 2, respectively. The compound Ph₂BiSbMes₂ (12), which has different substituents at the bismuth and antimony atoms, was isolated and fully characterised. In contrast, the isolation of Mes₂BiSbMes₂ (13) was not possible due to a dynamic equilibrium with Mes₄Bi₂ and Mes₄Sb₂ which was investigated via low-temperature ¹H-NMR spectroscopy in solution. The isolated compounds with a single bond between bismuth and the heavy pnictogens arsenic and antimony are rare examples of their kind. All isolated compounds (1-12) were characterised by NMR and IR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction.

The Dimethylbismuth Cation: Entry Into Dative Bi-Bi Bonding and Unconventional Methyl Exchange

The isolation of simple, fundamentally important, and highly reactive organometallic compounds remains among the most challenging tasks in synthetic chemistry. The detailed characterization of such compounds is key to the discovery of novel bonding scenarios and reactivity. The dimethylbismuth cation, [BiMe2 (SbF6 )] (1), has been isolated and characterized. Its reaction with BiMe3 gives access to an unprecedented dative bond, a Bi→Bi donor-acceptor interaction. The exchange of methyl groups (arguably the simplest hydrocarbon moiety) between different metal atoms is among the most principal types of reactions in organometallic chemistry. The reaction of 1 with BiMe3 enables an SE 2(back)-type methyl exchange, which is, for the first time, investigated in detail for isolable, (pseudo-)homoleptic main-group compounds.

Indirect Access to Carbene Adducts of Bismuth- and Antimony-Substituted Phosphaketene and Their Unusual Thermal Transformation to Dipnictines and [(NHC)2OCP][OCP]

The synthesis and thermal redox chemistry of the first antimony (Sb)– and bismuth (Bi)–phosphaketene adducts are described. When diphenylpnictogen chloride [Ph₂PnCl (Pn = Sb or Bi)] is reacted with sodium 2-phosphaethynolate [Na[OCP]·(dioxane)_x], tetraphenyldipnictogen (Ph₂Pn–PnPh₂) compounds are produced, and an insoluble precipitate forms from solution. In contrast, when the N-heterocyclic carbene adduct (NHC)–PnPh₂Cl is combined with [Na[OCP]·(dioxane)_x], Sb– and Bi–phosphaketene complexes are isolated. Thus, NHC serves as an essential mediator for the reaction. Immediately after the formation of an intermediary pnictogen–phosphaketene NHC adduct [NHC–PnPh₂(PCO)], the NHC ligand transfers from the Pn center to the phosphaketene carbon atom, forming NHC–C(O)P-PnPh₂ [Pn = Sb (3) or Bi (4)]. In the solid state, 3 and 4 are dimeric with short intermolecular Pn–Pn interactions. When compounds 3 and 4 are heated in THF at 90 and 70 °C, respectively, the pnictogen center Pn^III is thermally reduced to Pn^II to form tetraphenyldipnictines (Ph₂Pn–PnPh₂) and an unusual bis-carbene-supported OCP salt, [(NHC)₂OCP][OCP] (5). The formation of compound 5 and Ph₂Pn–PnPh₂ from 3 or 4 is unique in comparison to the known thermal reactivity for group 14 carbene–phosphaketene complexes, further highlighting the diverse reactivity of [OCP]⁻ with main-group elements. All new compounds have been fully characterized by single-crystal X-ray diffraction, multinuclear NMR spectroscopy (¹H, ¹³C, and ³¹P), infrared spectroscopy, and elemental analysis (1, 2, and 5). The electronic structure of 5 and the mechanism of formation were investigated using density functional theory (DFT).

An N-heterocyclic carbene (NHC) was used to support the otherwise unstable Ph₂Sb—P=C=O and Ph₂Bi—P=C=O moieties. Exploration of the thermal chemistry of these NHC−phosphaketene adducts reveals the formation of the salt [NHC₂OCP][OCP]. This present work demonstrates the thermal chemistry of the 2-phospaethynolate anion with heavier pnictogens (Sb and Bi).

Molecular bismuth(iii) monocations: structure, bonding, reactivity, and catalysis

Structurally defined, molecular bismuth(iii) cations show remarkable properties in coordination chemistry, Lewis acidity, and redox chemistry, allowing for unique applications in synthetic chemistry.

Squeezing Bi: PNP and P2N3 pincer complexes of bismuth

We report the first application of a rigid P2N3 pincer ligand in p-block chemistry by preparing its bismuth complex. We also report the first example of bismuth complexes featuring a flexible PNP pincer ligand, which shows phase-dependent structural dynamics. Highly electrophilic, albeit thermally unstable, Bi(iii) complexes of the PNP ligand were also prepared.

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

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.

Intramolecular Metal⋅⋅⋅π-Arene Interactions in Neutral and Cationic Main Group Compounds

The role of intramolecular metal⋅⋅⋅π-arene interactions has been investigated in the solid-state structures of a series of main group compounds supported by the bulky amide ligands, [N(^tBu Ar^≠ )(SiR₃ )]^- (^tBu Ar^≠ =2,6-(CHPh₂ )₂ -4-tBuC₆ H₂ , R=Me, Ph). The lithium and potassium amide salts showed different patterns of solvation and demonstrated that the SiPh₃ substituent is able to be involved in stabilizing the electrophilic metal. These group 1 metal compounds served as ligand transfer reagents to access a series of bismuth(III) halides. Chloride extraction from Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl₂ using AlCl₃ afforded the 1:1 salt [Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl][AlCl₄ ]. This was accompanied by a significant rearrangement of the stabilizing π-arene contacts in the solid-state. Attempted preparation of the corresponding tetraphenylborate salt resulted in phenyl-transfer and generation of the neutral Bi(N{^tBu Ar^≠ }{SiPh₃ })(Ph)Cl.

Neutral and cationic bismuth compounds supported by bis(amidodimethyl)disiloxane ligands

Bis(amidodimethyl)disiloxane ligands derived from O{SiMe₂N(H)R}₂ (abbreviated as (NON^R)H₂) are a stable support for neutral and cationic bismuth compounds. Attempts to extend the series Bi(NON^R)Cl (R = Ar = 2,6-iPr₂C₆H₃; R = tBu) to include compounds where R = Ar' = 2,6-Me₂C₆H₃ were complicated by concomitant formation of the bimetallic compound {Bi(NON^Ar')}₂(μ-NON^Ar'). Compounds containing [Bi(NON^R)]⁺ cations were obtained from reactions with group 13 chlorides MCl₃ (M = Al, Ga). X-ray crystallographic analysis showed intermolecular interactions with the [M_nCl_(3n+1)] anion.

Photoluminescence, semiconductive properties and theoretical calculation of a novel bismuth biimidazole compound

A novel bismuth biimidazole compound, [(BiCl₄ )-(μ₂ -Cl)₂ -(BiCl₄ )][(CH₃ )₄ -2,2'-biimidazole]₂ (1) with the (CH₃ )₄ -2,2'-biimidazole moiety generated in situ, was successfully prepared under hydrothermal conditions and structurally characterized using a single-crystal X-ray diffraction technique. Compound 1 is characteristic of an isolated structure, consisting of [(BiCl₄ )-(μ₂ -Cl)₂ -(BiCl₄ )] and (CH₃ )₄ -2,2'-biimidazole moieties. Solid-state photoluminescence measurement reveals that it shows a strong emission in the blue region. Time-dependent density functional theory studies show that this emission is ascribed to metal-to-ligand charge transfer. The solid-state diffuse reflectance spectrum reveals the existence of an optical band gap of 2.09 eV, indicating that it is a semiconductor.

Synthesis of mono-, di-, and triaminobismuthanes and observation of C–C coupling of aromatic systems with bismuth(iii) chloride

Mono-, di- or triaminobismuthanes were synthesized depending on the sterical demand of the organic substituent. In one case, a C–C coupling product was observed as main product in the reaction of BiCl₃ with Mes*(SiMe₃)NLi.

Reactivity of bis(organoamino)phosphanes with magnesium(ii) compounds

The reactivity of bis(organoamino)phosphanes with magnesium(ii) reagents is reported. The outcome of the reactions is influenced by a tautomeric H-shift in ligand backbones.

A neutral low-coordinate heterocyclic bismuth-tin species

The reaction of cyclodistannadiazane with an excess of antimonytrichloride led to the formation of tetrachlorodistibanes, while in the reaction with bismuthtrichloride a carbenoid bismuth species was obtained which can be regarded as a heavy atom analog of NHCs.