Activation and Catalytic Degradation of SF6 and PhSF5 at a Bismuth Center

In this work, we report the catalytic degradation of SF6 and PhSF5 using N,C,N pincer bismuthinidene complexes (1 and 5). Exposure of SF6 and PhSF5 to 1 results in the reduction of the S(VI) substrates and concomitant formation of Bi(III) and Bi(II) compounds, which were isolated and characterized. The oxidized bismuth-based products were demonstrated to undergo reduction with PMe3, recovering the starting complex 1. Having established a synthetic redox cycle, the catalytic degradation of SF6 and PhSF5 was developed through ligand optimization to 5, leading to a 528 TON for SF6 and the first reported TON for PhSF5 (3.2).

Bismuth in Radical Chemistry and Catalysis

Whereas indications of radical reactivity in bismuth compounds can be traced back to the 19th century, the preparation and characterization of both transient and persistent bismuth-radical species has only been established in recent decades. These advancements led to the emergence of the field of bismuth radical chemistry, mirroring the progress seen for other main-group elements. The seminal and fundamental studies in this area have ultimately paved the way for the development of catalytic methodologies involving bismuth-radical intermediates, a promising approach that remains largely untapped in the broad landscape of synthetic organic chemistry. In this review, we delve into the milestones that eventually led to the present state-of-the-art in the field of radical bismuth chemistry. Our focus aims at outlining the intrinsic discoveries in fundamental inorganic/organometallic chemistry and contextualizing their practical applications in organic synthesis and catalysis.

Xenobiotic Bi3+ Coordination by Cysteine-Rich Metallothionein-3 Reveals a Cooperatively Formed Thiolate-Sharing Bi2S5 Cluster

The field of designing artificial metalloproteins has yet to effectively tackle the incorporation of multimetal clusters, which is a key component of natural metalloproteins, such as metallothioneins (MTs) and calmodulin. MT is a physiological, essential, cysteine-rich metalloprotein that binds to a variety of metals but is only known to form metal-thiolate clusters with Cd2+, Zn2+, and Cu+. Bismuth is a xenobiotic metal and a component of metallodrugs used to treat gastric ulcers and cancer, as well as an emerging metal used in industrial practices. Electrospray ionization mass spectrometry, UV-visible spectroscopy, and extended X-ray absorption fine structure spectroscopy were used to probe the Bi3+ binding site structures in apo-MT3 (brain-located MT) at pH 7.4 and 2 and provide the complete set of binding affinities. We discovered the highly cooperative formation of a novel Bi3+ species, Bi2MT3, under physiological conditions, where each Bi3+ ion is coordinated by three cysteinyl thiolates, with one of the thiolates bridging between the two Bi3+ ions. This cluster structure was associated with a strong visible region absorption band, which was disrupted by the addition of Zn2+ and reversibly disrupted by acidification and increased temperature. This is the first reported presence of bridging cysteines for a xenobiotic metal in MT3 and the Bi2MT structure is the first Bi cluster found in a metalloprotein.

Organopnictogen(III) bis(arylthiolates) containing NCN-aryl pincer ligands: from synthesis and characterization to reactivity

Salt elimination reactions between organopnictogen(III) dichlorides, RPnCl₂ [R¹ = 2,6-(Me₂NCH₂)₂C₆H₃, Pn = Sb (1), Bi (2); R² = 2,6-{MeN(CH₂CH₂)₂NCH₂}₂C₆H₃, Pn = Sb (3), Bi (4); R³ = 2,6-{O(CH₂CH₂)₂NCH₂}₂C₆H₃, Pn = Sb (5), Bi (6)] and 2 equivalents of KSC₆H₃Me₂-2,6 afforded the isolation of a series of new NCN-chelated monoorganopnictogen(III) bis(arylthiolates), RPn(SC₆H₃Me₂-2,6)₂ [R¹, Pn = Sb (7), Bi (8); R², Pn = Sb (9), Bi (10); R³, Pn = Sb (11), Bi (12)]. Compounds 7 and 8 are unstable upon exposure to a dry O₂ atmosphere and their aerobic decomposition yields the monoorganopnictogen(III) oxides, cyclo-[2,6-(Me₂NCH₂)₂C₆H₃Pn(μ-O)]₂ [Pn = Sb (13), Bi (14)] with concomitant formation of the corresponding disulfide, ArS-SAr (Ar = C₆H₃Me₂-2,6). The oxidative addition of elemental sulfur or selenium to 7 undergoes a similar reaction path and gives stable heterocyclic species cyclo-[2,6-(Me₂NCH₂)₂C₆H₃Sb(μ-E)]₂ [E = S (15), Se (16)]. The reaction of 12 with I₂ (1 : 1 molar ratio) gives the diiodide [2,6-{O(CH₂CH₂)₂NCH₂}₂C₆H₃]BiI₂ (17), along with the S-S oxidative coupling by-product, ArS-SAr. The use of an excess of iodine affords the crystallization of a 2 : 1 iodine adduct of 17 (17·0.5I₂), built through halogen bonding. All new compounds were characterized by multinuclear NMR spectroscopy and ESI-MS as well as single crystal X-ray diffraction (except compounds 9 and 10).

Bismuth Redox Catalysis: An Emerging Main-Group Platform for Organic Synthesis

Bismuth has recently been shown to be able to maneuver between different oxidation states, enabling access to unique redox cycles that can be harnessed in the context of organic synthesis. Indeed, various catalytic Bi redox platforms have been discovered and revealed emerging opportunities in the field of main group redox catalysis. The goal of this perspective is to provide an overview of the synthetic methodologies that have been developed to date, which capitalize on the Bi redox cycling. Recent catalytic methods via low-valent Bi(II)/Bi(III), Bi(I)/Bi(III), and high-valent Bi(III)/Bi(V) redox couples are covered as well as their underlying mechanisms and key intermediates. In addition, we illustrate different design strategies stabilizing low-valent and high-valent bismuth species, and highlight the characteristic reactivity of bismuth complexes, compared to the lighter p-block and d-block elements. Although it is not redox catalysis in nature, we also discuss a recent example of non-Lewis acid, redox-neutral Bi(III) catalysis proceeding through catalytic organometallic steps. We close by discussing opportunities and future directions in this emerging field of catalysis. We hope that this Perspective will provide synthetic chemists with guiding principles for the future development of catalytic transformations employing bismuth.

Redox-Neutral Organometallic Elementary Steps at Bismuth: Catalytic Synthesis of Aryl Sulfonyl Fluorides

A Bi-catalyzed synthesis of sulfonyl fluorides from the corresponding (hetero)aryl boronic acids is presented. We demonstrate that the organobismuth(III) catalysts bearing a bis-aryl sulfone ligand backbone revolve through different canonical organometallic steps within the catalytic cycle without modifying the oxidation state. All steps have been validated, including the catalytic insertion of SO₂ into Bi-C bonds, leading to a structurally unique O-bound bismuth sulfinate complex. The catalytic protocol affords excellent yields for a wide range of aryl and heteroaryl boronic acids, displaying a wide functional group tolerance.

Catalytic Activation of N2O at a Low-Valent Bismuth Redox Platform

Herein we present the catalytic activation of N₂O at a Bi^I⇄Bi^III redox platform. The activation of such a kinetically inert molecule was achieved by the use of bismuthinidene catalysts, aided by HBpin as reducing agent. The protocol features remarkably mild conditions (25 °C, 1 bar N₂O), together with high turnover numbers (TON, up to 6700) and turnover frequencies (TOF). Analysis of the elementary steps enabled structural characterization of catalytically relevant intermediates after O-insertion, namely a rare arylbismuth oxo dimer and a unique monomeric arylbismuth hydroxide. This protocol represents a distinctive example of a main-group redox cycling for the catalytic activation of N₂O.

Water-Soluble Bismuth(III) Polynuclear Tyrosinehydroximate Metallamacrocyclic Complex: Structural Parallels to Lanthanide Metallacrowns

Recently there has been a great deal of interest and associated research into aspects of the coordination chemistry of lanthanides and bismuth-elements that show intriguing common features. This work focuses on the synthesis and characterization of a novel bismuth(III) polynuclear metallamacrocyclic complex derived from aminohydroxamic acid, in order to compare the coordination ability of Bi3+ with the similarly sized La3+ ions. A polynuclear tyrosinehydroximate Bi(OH)[15-MCCu(II)Tyrha-5](NO3)2 (1) was obtained according to the synthetic routes previously described for water-soluble Ln(III)-Cu(II) 15-MC-5 metallacrowns. Correlations between structural parameters of Bi(III) and Ln(III) complexes were analyzed. DFT calculations confirmed the similarity between molecular structures of the model bismuth(III) and lanthanum(III) tyrosinehydroximate 15-metallacrowns-5. Analysis of the electronic structures revealed, however, stronger donor-acceptor interactions between the central ion and the metallamacrocycle in the case of the lanthanum analogue. Thermochromic properties of 1 were studied.

The First Naked Bismuth-Chalcogen Metal Carbonyl Clusters: Extraordinary Nucleophilicity of the Bi Atom and Semiconducting Characteristics

Mixed bismuth-chalcogen-iron clusters [{EFe₃(CO)₉}Bi]^- [E = Te (1a) or Se (1b)] were produced via the reduction of BiCl₃ with [EFe₃(CO)₉]^2- under mild conditions. X-ray analysis showed that both clusters 1a and 1b had a square-pyramidal geometry, where the naked Bi and chalcogen both adopted a distorted trigonal-pyramidal configuration with a stereoactive lone pair. Complexes 1a and 1b can be further functionalized by methylation and metalation, which permits the nucleophilicity of the 6s/5s and 6s/4s lone pairs to be compared. In the metalation, the 6s pair of the Bi atom in 1a and 1b had an extraordinary nucleophilicity toward the unsaturated Cr(CO)₅ fragment, even in the presence of the more chemically active 5s or 4s pair, whereas in the case of methylation, only the 4s pair of Se could be selectively alkylated. Upon oxidation of 1a and 1b with suitable oxidizing agents, NaBiO₃ or K₂SeO₃, Bi-E bonded tetrahedral complexes [{EFe₂(CO)₆}Bi]^- [E = Te (4a) or Se (4b)] were formed by the elimination of one Fe(CO)₃ vertex. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and density functional theory (DFT) calculations showed that all of the Bi atoms in these complexes had oxidation states close to +1. Due to the electropositive character of the Bi atom, pronounced induced Bi···E inter- and intramolecular interactions were evident in 1a (1b), 4a (4b), and the metalated 3a (3b), where their linear-like ···Bi···E··· or zigzag-like ···Bi-E··· (E = Te or Se) chain or the Bi···E···E···Bi (E = Te or Se) dimeric chain can further expand into the two-dimensional network via nonclassical C-H···O(carbonyl) interactions, supported by noncovalent interaction index and DFT calculations. These positively charged Bi-induced Bi···E (E = Te or Se) and carbonyl-aided weak interactions can facilitate efficient electron transport within these ternary Bi-E-Fe or quaternary Bi-E-Fe-Cr cluster-based frameworks, resulting in semiconducting behavior with surprising ultranarrow energy gaps of 1.01-1.21 eV.

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.

Crystal structure of bis{5H-dibenzo[c,f][1,5]oxabismocin-12(7H)-yl} carbonate, C29H24O5Bi2

C29H24O5Bi2, orthorhombic, Pbca (no. 61), a = 14.8835(6) Å, b = 14.5551(6) Å, c = 23.6000(9) Å, V = 5112.5(4) Å3, Z = 8, R gt(F) = 0.0293, wR(F 2) = 0.0579, T = 296(2) K.

Dispersion interactions between neighboring Bi atoms in (BiH3 )2 and Te(BiR2 )2

Triggered by the observation of a short Bi⋯Bi distance and a BiTeBi bond angle of only 86.6° in the crystal structure of bis(diethylbismuthanyl)tellurane quantum chemical computations on interactions between neighboring Bi atoms in Te(BiR₂ )₂ molecules (R = H, Me, Et) and in (BiH₃ )₂ were undertaken. Bi⋯Bi distances atoms were found to significantly shorten upon inclusion of the d shells of the heavy metal atoms into the electron correlation treatment, and it was confirmed that interaction energies from spin component-scaled second-order Møller-Plesset theory (SCS-MP2) agree well with coupled-cluster singles and doubles theory including perturbative triples (CCSD(T)). Density functional theory-based symmetry-adapted perturbation theory (DFT-SAPT) was used to study the anisotropy of the interplay of dispersion attraction and steric repulsion between the Bi atoms. Finally, geometries and relative stabilities of syn-syn and syn-anti conformers of Te(BiR₂ )₂ (R = H, Me, Et) and interconversion barriers between them were computed. © 2018 Wiley Periodicals, Inc.

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.

Mixed triorganobismuthines RAr2Bi [Ar = C6F5, 2,4,6-(C6F5)3C6H2] and hypervalent racemic Bi-chiral diorganobismuth(iii) bromides RArBiBr (Ar = C6F5, Mes, Ph) with the ligand R = 2-(Me2NCH2)C6H4. Influences of the organic substituent

RAr₂Bi and chiral RArBiBr were structurally characterized; N–Bi bond distances in RArBiBr appear to be similar regardless of the electronic properties of the Ar ligand.

A general route to monoorganopnicogen(III) (M = Sb, Bi) compounds with a pincer (N,C,N) group and oxo ligands

The reaction of RMCl2 [R = 2,6-[MeN(CH2CH2)2NCH2]2C6H3; M = Sb (1), Bi (2)] with KOH affords the isolation of the oxides cyclo-R2M2O2 [M = Sb (3), Bi (4)]. Treatment of 3 with trifluoroacetic acid produced an ionic species (5) with a dinuclear cation that contains organic ligands protonated partially at one of the pendant arms. The cyclic oxides 3 and 4 are able to trap gaseous CO2 to give “RMCO3” [M = Sb (6), Bi (7)], the degree of these organometallic carbonates’ oligomerization being under investigation. The reactivity of the dinuclear oxide 3 was also investigated towards oxalic acid or dopamine hydrochloride and pure mononuclear compounds could be isolated, i.e. RSb[O(O)CC(O)O] (8) and RSb[O2-1,2-C6H3-3-(CH2)2NH3]Cl (9). The reaction of the dichlorides 1 and 2 with ethylene glycol, pinacol or catechol, in the presence of KOH, led to 2-organo-1,3,2-dioxastibolanes or -bismolanes RM(OCH2)2 [M = Sb (10), Bi (11)], RM(OCMe2)2 [M = Sb (12), Bi (13)] and 2-organo-1,3,2-dioxastibole or -bismole RM(O2-1,2-C6H4) [M = Sb (14), Bi (15)], respectively. The compounds were investigated by NMR spectroscopy, including variable temperature experiments, providing evidence for the presence of the intramolecular N→M interactions in solution. Single crystal X-ray diffraction studies were performed for most compounds and revealed an organic group R acting as a pincer ligand resulting in a distorted square pyramidal (N,C,N)MO2 core with cis intramolecular N→M interactions placed trans to M–O bonds. This is in contrast to the N→M interactions trans to each other as found in the RMCl2 used as starting materials. The crystals of the oxides 3 and 4·4H2O contain different geometric isomers with anti and syn orientation of the M–C bonds, respectively, with respect to the planar M2O2 ring. In the supramolecular polymeric architecture established in the crystal of 4·4H2O an important finding is the experimental observation of water hexamer units with a [tetramer + 2] structure (water molecules connected to opposite corners of a square water tetramer) fixed between 1D-chains of the type (syn-R2Bi2O2·H2O)n through additional hydrogen bonds to oxygen atoms of the dinuclear organobismuth(III) moieties. Theoretical calculations were carried out on 2–6 and 8–15 in order to gain insight into the stabilization energy produced by intramolecular coordination of the pendant arms, association degrees and formation energies of the organopnicogen compounds with chelating ligands.

Organomercury(II) and tellurium(II) compounds with the "pincer" ligand 2,6-[O(CH2CH2)2NCH2]2C6H3--stabilization of an unusual organotellurium(II) cationic species

The reaction of RH (1) with Hg(OAc)(2), in EtOH, gave the acetate RHgOAc (2) [R = 2,6-[O(CH(2)CH(2))(2)NCH(2)](2)C(6)H(3)]. The corresponding RHgCl (3) was obtained from 2 and LiCl. The reaction of 3 with TeCl(4) (1:1 molar ratio), in anhydrous 1,4-dioxane, resulted in the transfer of the organic ligand from mercury to tellurium and the isolation of the unexpected ionic compounds [RTe](2)[Hg(2)Cl(6)] (4) and [RH(3)][HgCl(4)] (5). The molecular structures of 1-4 and 5·H(2)O were established by single-crystal X-ray diffraction. The acetate 2 and the chloride 3 are monomeric in solid state. In both mercury and tellurium organometallic compounds the organic group acts as an (N,C,N) "pincer" ligand. This coordination pattern provided stability for the rare [RTe](+) cation. Weak cation-anion interactions [Te···Cl 3.869(3) Å] are present between [RTe](+) and the dinuclear anion [Hg(2)Cl(6)](2-) in the crystal of 4. Theoretical calculations with DFT methods were performed for models of 3 and 4. The results show that in the cation of 4 the coordination of the nitrogen atoms play an important role for the stabilization of the structure found in the crystal whereas in 3 the coordination of the nitrogen atoms to the metal centre stabilizes to a less extent the structure found in solid state.