Carbodicarbene Bismaalkene Cations: Unravelling the Complexities of Carbene versus Carbone in Heavy Pnictogen Chemistry

Metal-Mediated Synthesis of a Mixed Arduengo-Fischer Carbodicarbene Ligand

Carbodicarbenes are strong C-donor ligands, which have found numerous applications in organometallic and main group element chemistry. Herein, we report a structurally distinct carbodicarbene ligand, which is formed by dinitrogenative coupling of a Fischer carbene complex with an N-heterocyclic diazoolefin. The resulting carbonyl complex serves as a stable source for the mixed Arduengo-Fischer carbodicarbene ligand. Facile ligand transfer reactions were demonstrated to occur with gold(I), copper(I), palladium(II), and rhodium(I) complexes.

InnTl4-nH+ (n = 0∼4): Tetracoordinate Hydrogen in a Planar Fashion?

The recent report of planar tetracoordinate hydrogen (ptH) in In4H+ is very intriguing in planar hypercoordinate chemistry. Our high-level CCSD(T) calculations revealed that the proposed D4h-symmetric ptH In4H+ is a first-order saddle point with an imaginary frequency in the out-of-plane mode of the hydrogen atom. In fact, at the CCSD(T)/aug-cc-pV5Z/aug-cc-pV5Z-PP level, the C4v isomer, with the H atom located 0.70 Å above the In4 plane, is 0.5 kcal/mol more stable than the D4h isomer. However, given the small perturbation from planarity and essentially barrierless C4v ↔ D4h ↔ C4v transition, the vibrationally averaged structure can still be considered as a planar. Extending our exploration to the InnTl4-nH+ (n = 0-3) systems, we found all these ptH structures, except for In2Tl2H+, to be the putative global minimum. The single σ-delocalized interaction between the central hydrogen atom and InnTl4-n ligand rings proves pivotal in establishing planarity and aromaticity and conferring substantial stability upon these rule-breaking ptH species.

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.

The Chlorido-Bismuth Dication: A Potent Lewis Acid Captured in a Hepta-Coordinate Species with a Stereochemically Active Lone Pair

The stabilization of simple, highly reactive cationic species in molecular complexes represents an important strategy to isolate and characterize compounds with uncommon or even unprecedented structural motifs and properties. Here we report the synthesis, isolation, and full characterization of chlorido-bismuth dications, stabilized only by monodentate dimethylsulfoxide (dmso) ligands: [BiCl(dmso)6][BF4]2 (1) and [BiCl(μ2-dmso)(dmso)4]2[BF4]4 (2). These compounds show unusual distorted pentagonal bipyramidal coordination geometries along with high Lewis acidities and have been analyzed by multinuclear NMR spectroscopy, elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, and density functional theory calculations. Attempts to generate the bromido- and iodido-analogs gave dmso-stabilized tricationic bismuth species.

Ligand Exchange at Carbon: Synthetic Entry to Elusive Species and Versatile Reagents

How different is carbon compared to other elements in the periodic table? Can carbon compounds be regarded as coordination complexes with carbon as the central element undergoing a facile exchange of its ligands? Although carbon clearly plays a special role among the elements of the periodic table, recent studies have drawn parallels between the bonding situation and the reactivity of carbon compounds to transition metal complexes. This Perspective summarizes recent reports about ylidic and zwitterionic compounds that were shown to exhibit ambiguous bonding situations that can be interpreted as donor-acceptor interactions similar to the bond between a metal and a neutral ligand. Based on this conception, ligand exchange reactions prototypical of transition metal complexes were realized at carbon atoms, enabling new synthetic strategies for the synthesis of reactive species and building blocks. In particular, the exchange of N2, CO, and phosphine ligands led to the development of a mild method for accessing new compounds and reagents with unusual properties, such as vinylidene ketenes or stable ketenyl anions, that open up a diverse but still poorly explored follow-up chemistry.

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.

Air- and photo-stable luminescent carbodicarbene-azaboraacenium ions

Substitution of a C=C bond by an isoelectronic B-N bond is a well-established strategy to alter the electronic structure and stability of acenes. BN-substituted acenes that possess narrow energy gaps have attractive optoelectronic properties. However, they are susceptible to air and/or light. Here we present the design, synthesis and molecular structures of fully π-conjugated cationic BN-doped acenes stabilized by carbodicarbene ligands. They are luminescent in the solution and solid states and show high air and moisture stability. Compared with their neutral BN-substituted counterparts as well as the parent all-carbon acenes, these species display improved quantum yields and small optical gaps. The electronic structures of the azabora-anthracene and azabora-tetracene cations resemble higher-order acenes while possessing high photo-oxidative resistance. Investigations using density functional theory suggest that the stability and photo-physics of these conjugated systems may be ascribed to their cationic nature and the electronic properties of the carbodicarbene.

Geminal bimetallic coordination of a carbone to main-group and transition metals

The non-bonding carbone lone pair in geometrically-constrained antimony and bismuth carbodiphosphorane complexes readily complexed AuCl to afford rare examples of geminal bimetallic carbone coordination featuring a main-group metal.

Synthesis and Reactivity of an Anionic Diazoolefin

Bent (hetero)allenes such as carbodicarbenes and carbodiphosphoranes can act as neutral C-donor ligands, and diverse applications in coordination chemistry have been reported. N-Heterocyclic diazoolefins are heterocumulenes, which can function in a similar fashion as L-type ligands. Herein, we describe the synthesis and the reactivity of an anionic diazoolefin. This compound displays distinct reactivity compared to neutral diazoolefins, as evidenced by the preparation of diazo compounds via protonation, alkylation, or silylation. The anionic diazoolefin can be employed as an ambidentate, X-type ligand in salt metathesis reactions with metal halide complexes. Extrusion of dinitrogen was observed in a reaction with PCl(NiPr2 )2 , resulting in a stable phosphinocarbene.

Binuclear Macrocyclic Silver(I) Complex of a Bis(carbone) Pincer Ligand: Synthesis and Application as a Carbone-Transfer Agent

A facile synthesis of a binuclear AgI complex 2 of a bis(carbone) ligand L and its application as a carbone-transfer agent for the generation of other transition-metal complexes of AuI (3), NiII (4), and PdII (5) is presented. Complex 2 was synthesized through multiple synthetic routes under mild reaction conditions using the tetracationic [LH4][OTf·Cl]2 precursor salt, the dicationic [LH2][OTf]2 ylide salt, and the free ligand L. The first two synthesis routes require no prior isolation of the air-, moisture-, and temperature-sensitive free ligand L, thus affording complex 2 with high yield and purity. Multinuclear NMR techniques, high-resolution mass spectrometry, and single-crystal X-ray diffraction analysis confirmed the identity of complex 2 as a binuclear AgI complex of L with a molecular formula of [L2Ag2][OTf]2 and a 16-membered-ring metallomacrocyclic structure. During the transmetalation reaction with AuI, the binuclear nature of complex 2 remains intact to give analogous complex 3 ([L2Au2][OTf]2). However, the dimeric structure was disrupted upon the carbone-transfer reaction with NiII and PdII, yielding mononuclear C-N-C pincer-type complexes 4 ([LNiCl][OTf]) and 5 ([LPdCl][OTf]), respectively. These results demonstrated the versatile use of complex 2 as a carbone-transfer agent to other transition metals regardless of the type or size of the metals or the geometry they prefer.

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.

Counterintuitive Chemistry: Carbene Stabilization of Zero-Oxidation State Main Group Species

Carbenes have evolved from transient laboratory curiosities to a robust, diverse, and surprisingly impactful ligand class. A variety of different carbenes have significantly contributed to the development of low-oxidation state main group chemistry. This Perspective focuses upon advances in the chemistry of carbene complexes containing main group element cores in the formal oxidation state of zero, including their diverse synthetic strategies, unusual bonding and structural motifs, and utility in transition metal coordination chemistry and activation of small molecules.

Carbodicarbenes and Striking Redox Transitions of their Conjugate Acids: Influence of NHC versus CAAC as Donor Substituents

Herein, a new type of carbodicarbene (CDC) comprising two different classes of carbenes is reported; NHC and CAAC as donor substituents and compare the molecular structure and coordination to Au(I)Cl to those of NHC-only and CAAC-only analogues. The conjugate acids of these three CDCs exhibit notable redox properties. Their reactions with [NO][SbF₆ ] were investigated. The reduction of the conjugate acid of CAAC-only based CDC with KC₈ results in the formation of hydrogen abstracted/eliminated products, which proceed through a neutral radical intermediate, detected by EPR spectroscopy. In contrast, the reduction of conjugate acids of NHC-only and NHC/CAAC based CDCs led to intermolecular reductive (reversible) carbon-carbon sigma bond formation. The resulting relatively elongated carbon-carbon sigma bonds were found to be readily oxidized. They were, thus, demonstrated to be potent reducing agents, underlining their potential utility as organic electron donors and n-dopants in organic semiconductor molecules.

Isolation of an Annulated 1,4-Distibabenzene Diradicaloid

The first 1,4-distibabenzene-1,4-diide compound [(ADC)Sb]₂ (5) based on an anionic dicarbene (ADC) (ADC=PhC{N(Dipp)C}₂ , Dipp=2,6-iPr₂ C₆ H₃ ) is reported as a bordeaux-red solid. Compound 5, featuring a central six-membered C₄ Sb₂ ring with formally Sb^I atoms may be regarded as a base-stabilized cyclic bis-stibinidene in which each of the Sb atoms bears two lone-pairs of electrons. 5 undergoes 2 e-oxidation with Ph₃ C[B(C₆ F₅ )₄ ] to afford [(ADC)Sb]₂ [B(C₆ F₅ )₄ ]₂ (6) as a brick-red solid. Each of the Sb atoms of 6 has an unpaired electron and a lone-pair. The broken-symmetry open-shell singlet diradical solution for (6)²⁺ is calculated to be 2.13 kcal mol^-1 more stable than the closed-shell singlet. The diradical character of (6)²⁺ according to SS-CASSCF (state-specific complete active space self-consistent field) and UHF (unrestricted Hartree-Fock) methods amounts to 36 % and 39 %, respectively. Treatments of 6 with (PhE)₂ yield [(ADC)Sb(EPh)]₂ [B(C₆ F₅ )₄ ]₂ (7-E) (E=S or Se). Reaction of 5 with (cod)Mo(CO)₄ affords [(ADC)Sb]₂ Mo(CO)₄ (8).

Crystallographic evidence for a continuum and reversal of roles in primary-secondary interactions in antimony Lewis acids: applications in carbonyl activation

Primary and secondary interactions form the basis of substrate activation in Lewis-acid mediated catalysis, with most substrate activations occurring at the secondary binding site. We explore two series of antimony cations, [(NMe₂CH₂C₆H₄)(mesityl)Sb]⁺ (A) and [(NMe₂C₆H₄)(mesityl)Sb]⁺ (B), by coordinating ligands with varying nucleophilicity at the position trans to the N-donor. The decreased nucleophilicity of the incoming ligands leads to reversal from a primary bond to a secondary interaction in A, whereas a constrained N-coordination in B diminishes the border between primary and secondary bonding. Investigations on carbonyl olefin metathesis reactions and carbonyl reduction demonstrate increased reactivity of a Lewis acid when the substrate activation occurs at the primary binding site.

Dihalo bismuth cations: unusual coordination properties and inverse solvent effects in Lewis acidity

A series of well-defined cationic hepta-coordinate bismuth halides [BiX₂(py)₅][B(3,5-(CF₃)₂-C₆H₃)₄] (X = Cl, Br, I), stabilized only by substitutionally labile solvent molecules, were synthesized and fully characterized. Their apparent D_5h symmetry with a lone pair at the central atom is unprecedented for main group compounds. The potential of BiX₃ to show unexpectedly high Lewis acidities in moderately polar solvents is likely due to the formation of [BiX₂(solv)₅]⁺ and related ionic species.

A Bis-(carbone) Pincer Ligand and Its Coordinative Behavior toward Multi-Metallic Configurations

Carbones are divalent carbon(0) species that contain two lone pairs of electrons. Herein, we have prepared the first known stable and isolable free bis-(carbone) pincer framework with a well-defined solid-state structure. This bis-(carbone) ligand is an effective scaffold for forming monometallic (Ni and Pd) and trinuclear heterometallic complexes with Au-Pd-Au, Au-Ni-Au, and Cu-Ni-Cu configurations. Sophisticated quantum-theoretical analyses found that the metal-metal interactions are too weak to play a significant role in upholding these multi-metallic configurations; rather, the four lone pairs of electrons within the bis-(carbone) framework are the main contributors to the stability of the complexes.

Air-Stable Thermoluminescent Carbodicarbene-Borafluorenium Ions

Borenium ions, originally synthesized as fundamentally important laboratory curiosities, have attracted significant attention due to their applications in catalysis and frustrated Lewis pair chemistry. However, investigations of the materials properties of these types of compounds are exceptionally rare. Herein, we report the synthesis, molecular structures, and optical properties of a new class of air-stable borenium ions, stabilized by the strongly donating carbodicarbene (CDC) ligand (2, 3, 6). Notably, CDC-borafluorenium ions exhibit thermoluminescence in solution, a result of a twisted intramolecular charge transfer process. The temperature responsiveness, which is observable by the naked eye, is assessed over a 20 to -60 °C range. Significantly, compound 2 emits white light at lower temperatures. In the solid state, these borocations exhibit increased quantum yields due to aggregation-induced emission. CDC-borafluorenium ions with two different counteranions (Br^-, BPh₄^-) were investigated to evaluate the effect of anion size on the solution and solid-state optical properties. In addition, CDCs containing both symmetrical and unsymmetrical N-heterocycles (bis(1-isopropyl-3-methylbenzimidazol-2-ylidene)methane and bis(1,3-dimethyl-1,3-dihydro-2H-benzo[d]imidazol-2-ylidene)methane) were tested to understand the implications of free rotation about the CDC ligand carbon-carbon bonds. The experimental work is complemented by a comprehensive theoretical analysis of the excited-state dynamics.

Unveiling the Electronic Structure of the Bi(+1)/Bi(+3) Redox Couple on NCN and NNN Pincer Complexes

Low-valent group 15 compounds stabilized by pincer ligands have gained particular interest, given their direct access to fine-tune their reactivity by the coordination pattern. Recently, bismuth has been employed in a variety of catalytic transformations by taking advantage of the (+1/+3) redox couple. In this work, we present a detailed quantum–chemical study on the electronic structure of bismuth pincer complexes from two different families, namely, bis(ketimine)phenyl (NCN) and triamide bismuthinidene (NNN). The use of the so-called effective oxidation state analysis allows the unambiguous assignation of the bismuth oxidation state. In contrast to previous studies, our calculations suggest a Bi(+1) assignation for NCN pincer ligands, while Bi(+3) character is found for NNN pincer complexes. Notably, regardless of its oxidation state, the central bismuth atom disposes of up to two lone pairs for coordinating Lewis acids, as indicated by very high first and second proton affinity values. Besides, the Bi–NNN systems can also accommodate two Lewis base ligands, indicating also ambiphilic behavior. The effective fragment orbital analysis of Bi and the ligand allows monitoring of the intricate electron flow of these processes, revealing the noninnocent nature of the NNN ligand, in contrast with the NCN one. By the dissection of the electron density into effective fragment orbitals, we are able to quantify and rationalize the Lewis base/acid character.

Effective oxidation state analysis sheds light on the electronic structure of chemical systems. The oxidation state of bismuthinidene pincer complexes can be assigned as Bi(+1) or Bi(+3) depending on the nature of the ligands. Despite this assignation, the reactivity pattern as Lewis base or acid is similar. The occupation of the effective fragment orbitals gives a straightforward method to quantify the reactivity.

Recent Developments in the Chemistry of Pn(I) (Pn=N, P, As, Sb, Bi) Cations

The Group 15 Pn(I) cations (Pn=N, P, As, Sb and Bi), which are isoelectronic with the donor-stabilized carbones, have emerged recently. Despite the presence of two lone pair of electrons, the Pn(I) cations are weakly nucleophilic due to their inherent positive charge. Strongly electron-donating supporting ligands including zwitterionic forms have been used to enhance their Lewis basicity. Furthermore, the chelating effect of cyclic ligand systems proved effective in increasing their nucleophilicity. The strategies involved in successfully isolating the fleeting Sb(I) and Bi(I) cations as the recent most achievements in this field have been discussed. The syntheses, structure, bonding situations and reactivity of the Pn(I) cations are discussed. An outlook on the periodic trends and future applications of these electronically unique electron-rich cationic moieties have been provided.

Stabilization of the Elusive Antimony(I) Cation and Its Coordination Complexes with Transition Metals

Upon stabilization by 5,6-bis(diisopropylphosphino)acenaphthene to form compound 1, the fugitive antimony (I) cation exhibited nucleophilic behavior towards coinage metals. Compound 1 was strategically synthesized at room temperature from SbCl₃ , the bis(phosphine), and trimethylsilyl trifluoromethanesulfonate taken in a 1:2:3 ratio, whereby the bis(phosphine) plays the dual role of a reductant and a supporting ligand. The generation of 1 involves two-electron oxidation of the ligand to form a P-P bonded diphosphonium dication. Compound 1 was separated from this dication to give both products in pure form in moderate yields. Despite the overall positive charge, the Sb^I site in 1 was found to bind to metal centers, forming complexes with Au^I , Ag^I and Cu^I . Compound 1 reduced Cu^II to Cu^I and formed a coordination complex with the resulting Cu^I species. The effects of the electron-rich bis(phosphine) and the constrained peri geometry in stabilizing and enhancing the nucleophilicity of 1 have been rationalized through computational studies.

Reversing Lewis acidity from bismuth to antimony

Investigations on the boundaries between the neutral and cationic models of (Mesityl)₂EX (E = Sb, Bi and X = Cl^-, OTf^-) have facilitated reversing the Lewis acidity from bismuth to antimony. We use this concept to demonstrate a higher efficiency of (Mesityl)₂SbOTf over (Mesityl)₂BiOTf in the catalytic reduction of phosphine oxides to phosphines. The experiments supported with computations described herein will find use in designing new Lewis acids relevant to catalysis.

Isolation of a Uranium(III)-Carbon Multiple Bond Complex

Low-valent uranium-element multiple bond complexes remain scarce, though there is burgeoning interest regarding to their bonding and reactivity. Herein, isolation of a uranium(III)-carbon double bond complex [(Cp*)2 U(CDP)](BPh4 ) (1) comprising a tridentate carbodiphosphorane (CDP) was reported for the first time. Oxidation of 1 afforded the corresponding U(IV) complex [(Cp*)2 U(CDP)](BPh4 )2 (2). The distance between U and C in 2 is 2.481 Å, indicating the existence of a typical U=C double bond, which is further confirmed by quantum chemical calculations. Bonding analysis suggested that the CDP also serves as both σ- and π-donor in complex 1, though a longer U-C bond (2.666(3) Å) is observed. It implies that 1 is the first isolable mononuclear uranium(III) carbene complex. Moreover, these results suggest that CDPs are promising ligands to establish other low-valent f-block metal-carbon multiple bond complexes.

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).

Carbodicarbene Bismaalkene Cations: Unravelling the Complexities of Carbene versus Carbone in Heavy Pnictogen Chemistry

We report a combined experimental and theoretical study on the first examples of carbodicarbene (CDC)-stabilized bismuth complexes, which feature low-coordinate cationic bismuth centers with C=Bi multiple-bond character. Monocations [(CDC)Bi(Ph)Cl][SbF6 ] (8) and [(CDC)BiBr2 (THF)2 ][SbF6 ] (11), dications [(CDC)Bi(Ph)][SbF6 ]2 (9) and [(CDC)BiBr(THF)3 ][NTf2 ]2 (12), and trication [(CDC)2 Bi][NTf2 ]3 (13) have been synthesized via sequential halide abstractions from (CDC)Bi(Ph)Cl2 (7) and (CDC)BiBr3 (10). Notably, the dications and trication exhibit C ⇉ Bi double dative bonds and thus represent unprecedented bismaalkene cations. The synthesis of these species highlights a unique non-reductive route to C-Bi π-bonding character. The CDC-[Bi] complexes (7-13) were compared with related NHC-[Bi] complexes (1, 3-6) and show substantially different structural properties. Indeed, the CDC ligand has a remarkable influence on the overall stability of the resulting low-coordinate Bi complexes, suggesting that CDC is a superior ligand to NHC in heavy pnictogen chemistry.

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.