Cyclic Hydrocarbon Frameworks Containing Two Bismuth Atoms: Towards 9,10-Dibismaanthracene

When bismuth atoms are incorporated into cyclic organic systems, this commonly goes along with strained or distorted molecular geometries, which can be exploited to modulate the physical and chemical properties of these compounds. In six-membered heterocycles, bismuth atoms are often accompanied by oxygen, sulfur or nitrogen as a second hetero-element. In this work, we present the first examples of six-membered rings, in which two CH units are replaced by BiX moieties (X=Cl, Br, I), resulting in dihydro-anthracene analogs. Their behavior in chemically reversible reduction reactions is explored, aiming at the generation of dibisma-anthracene (bismanthrene). Heterometallic compounds (Bi/Fe, Bi/Mn) are introduced as potential bismanthrene surrogates, as supported by bismanthrene-transfer to selenium. Analytical techniques used to investigate the reported compounds include NMR spectroscopy, high-resolution mass spectrometry, single-crystal X-ray diffraction analyses, and DFT calculations.

Fusing Triphenylbismuth and PnPh3 (Pn = P-Bi): Synthesis, Isolation, and Characterization of 9-Bisma-10-Pnictatriptycenes

The first series of 9-bisma-10-pnictatriptycenes Bi(C6H4)3Pn (2-Pn, Pn = P-Bi; see graphic) has been synthesized in a two-step procedure via suitable tris(2-bromophenyl)pnictanes 1-Pn and characterized in solution as well as in the solid state. DFT calculations suggest preferential interactions between 2-Pn and soft Lewis acids via the lighter pnictogen donor atom. Experimental studies demonstrate that even the weakest Lewis base in the series of 2-Pn, namely the dibismatriptycene 2-Bi, interacts with Lewis acidic [BiMe2(SbF6)] in solution. Analytical techniques include (VT-)NMR spectroscopy, DOSY NMR spectroscopy, high-resolution mass spectrometry, single-crystal X-ray diffraction analyses, and DFT calculations.

Bismuth in Dynamic Covalent Chemistry: Access to a Bowl-Type Macrocycle and a Barrel-Type Heptanuclear Complex Cation

Dynamic covalent chemistry (DCvC) is a powerful and widely applied tool in modern synthetic chemistry, which is based on the reversible cleavage and formation of covalent bonds. One of the inherent strengths of this approach is the perspective to reversibly generate in an operationally simple approach novel structural motifs that are difficult or impossible to access with more traditional methods and require multiple bond cleaving and bond forming steps. To date, these fundamentally important synthetic and conceptual challenges in the context of DCvC have predominantly been tackled by exploiting compounds of lighter p-block elements, even though heavier p-block elements show low bond dissociation energies and appear to be ideally suited for this approach. Here we show that a dinuclear organometallic bismuth compound, containing BiMe2 groups that are connected by a thioxanthene linker, readily undergoes selective and reversible cleavage of its Bi-C bonds upon exposure to external stimuli. The exploitation of DCvC in the field of organometallic heavy p-block chemistry grants access to unprecedented macrocyclic and barrel-type oligonuclear compounds.

Small molecule activation by well-defined compounds of heavy p-block elements

The creative design and exploration of new bonding motifs and molecular architectures in main group chemistry have pushed the boundaries of reactivity in this field of research. In this context, the activation of small molecules represents a set of benchmark reactions and offers valuable opportunities for the development of innovative synthetic methods. In addition to significant progress by use of transition metal complexes and compounds of lighter p-block elements, compounds based on heavy p-block elements (with the principle quantum number n > 4) have seen major advances in recent years. Fundamental properties originating from their high atomic number (such as the size, energy, and polarizability of atomic orbitals) set them apart from more established species in small molecule activation. Challenges and opportunities arising from this scenario are analyzed and highlighted.

Insertion of CO2 and CS2 into Bi-N bonds enables catalyzed CH-activation and light-induced bismuthinidene transfer

The uptake and release of small molecules continue to be challenging tasks of utmost importance in synthetic chemistry. The combination of such small molecule activation with subsequent transformations to generate unusual reactivity patterns opens up new prospects for this field of research. Here, we report the reaction of CO₂ and CS₂ with cationic bismuth(iii) amides. CO₂-uptake gives isolable, but metastable compounds, which upon release of CO₂ undergo CH activation. These transformations could be transferred to the catalytic regime, which formally corresponds to a CO₂-catalyzed CH activation. The CS₂-insertion products are thermally stable, but undergo a highly selective reductive elimination under photochemical conditions to give benzothiazolethiones. The low-valent inorganic product of this reaction, Bi(i)OTf, could be trapped, showcasing the first example of light-induced bismuthinidene transfer.

Bismuth Cations: Fluoride Ion Abstraction, Isocyanide Coordination, and Impact of Steric Bulk on Lewis Acidity

Invited for the cover of this issue are the groups of Carsten von Hänisch and Crispin Lichtenberg at the Philipps University of Marburg. The image depicts a bismuth kraken, eagerly grabbing Lewis basic substrates, thereby solving scientific puzzles about bismuth-based Lewis acidity. Read the full text of the article at 10.1002/chem.202204012.

Reactivity of a Cationic Bismuth Amide towards Unsymmetric Heterocumulenes

Invited for this month's cover is the Lichtenberg group of the Philipps-University Marburg (Germany). The front cover picture shows "bismuth" dressed in colors reminiscent of those found on the surface of this element. In the graphic, bismuth is craving for soft ice cream. This represents the preference of Lewis acidic bismuth centers for soft donor atoms, as demonstrated in the insertion of heterocumulenes into the Bi-N bond of a cationic bismuth amide. More information can be found in the Research Article by Crispin Lichtenberg and co-workers.

Bonding in Low-Coordinated Organoarsenic and Organoantimony Compounds: A Threshold Photoelectron Spectroscopic Investigation

Methyl and methylene compounds of arsenic and antimony are studied by photoelectron photoion coincidence spectroscopy to investigate their relative stability. While for As both HAs=CH2, As-CH3 and the methylene compound As=CH2 are identified in the spectrum, the only Sb compound observed is Sb-CH3. Thus, there is a step in the main group 15 between As and Sb, regarding the relative stability of the methyl compounds. Ionization energies, vibrational frequencies and spin-orbit splittings are determined for the methyl compound from photoion mass-selected photoelectron spectra. Although the spectroscopic results for organoantimony resemble those for the previously investigated bismuth compounds, EPR spectroscopic experiments indicate for Sb(CH3)3 a far lower tendency for methyl transfer compared to Bi(CH3)3. The present study concludes investigations on low-valent organopnictogen compounds.

Bismuth Cations: Fluoride Ion Abstraction, Isocyanide Coordination, and Impact of Steric Bulk on Lewis Acidity

The molecular compound [BiDipp2(SbF6)], containing the bulky, donor-free bismuth cation [BiDipp2]+ has been synthesized and fully characterized (Dipp = 2,6-iPr2-C6H3). Using its methyl analog [BiMe2(SbF6)] as a second reference point, the impact of steric bulk on bismuth-based Lewis acidity has been investigated in a combined experimental (Gutmann-Beckett method and modified Gutmann-Beckett method) and theoretical approach (DFT calculations). Reactivity studies of the bismuth cations towards (PF6)- and neutral Lewis bases such as isocyanides C≡NR' have revealed facile fluoride ion abstraction and straightforward Lewis pair formation, respectively. The first examples of compounds featuring bismuth-bound isocyanides have been isolated and fully characterized.

Charge Makes a Difference: Molecular Ionic Bismuth Compounds

Key challenges in modern synthetic chemistry include the design of reliable, selective, and more sustainable synthetic methods, as well as the development of promising candidates for new materials. Molecular bismuth compounds offer valuable opportunities as they show an intriguing spectrum of properties that is yet to be fully exploited: a soft character, a rich coordination chemistry, the availability of a broad variety of oxidation states (at least +V to -I) and formal charges (at least +3 to -3) at the Bi atoms, and reversible switching between multiple oxidation states. All this is paired with the status of a non-precious (semi-)metal of good availability and a tendency towards low toxicity. Recent findings show that some of these properties only come into reach, or can be substantially optimized, when charged compounds are specifically addressed. In this review, essential contributions to the synthesis, analyses, and utilization of ionic bismuth compounds are highlighted.

Aromatic 1,2-Azaborinin-1-yls as Electron-Withdrawing Anionic Nitrogen Ligands for Main Group Elements

The 2-aryl-3,4,5,6-tetraphenyl-1,2-azaborinines 1-EMe₃ and 2-EMe₃ (E=Si, Sn; aryl=Ph (1), Mes (=2,4,6-trimethylphenyl, 2)) were synthesized by ring-expansion of borole precursors with N₃ EMe₃ -derived nitrenes. Desilylative hydrolysis of 1- and 2-SiMe₃ yielded the corresponding N-protonated azaborinines, which were deprotonated with nBuLi or MN(SiMe₃ )₂ (M=Na, K) to the corresponding group 1 salts, 1-M and 2-M. While the lithium salts crystallized as monomeric Lewis base adducts, the potassium salts formed coordination polymers or oligomers via intramolecular K⋅⋅⋅aryl π interactions. The reaction of 1-M or 2-M with CO₂ yielded N-carboxylate salts, which were derivatized by salt metathesis to methyl and silyl esters. Salt metathesis of 1-M or 2-M with methyl triflate, [Cp*BeCl] (Cp*=C₅ Me₅ ), BBr₂ Ar (Ar=Ph, Mes, 2-thienyl), ECl₃ (E=B, Al, Ga) and PX₃ (X=Cl, Br) afforded the respective group 2, 13 and 15 1,2-azaborinin-2-yl complexes. Salt metathesis of 1-K with BBr₃ resulted not only in N-borylation but also Ph-Br exchange between the endocyclic and exocyclic boron atoms. Solution ¹¹ B NMR data suggest that the 1,2-azaborinin-2-yl ligand is similarly electron-withdrawing to a bromide. In the solid state the endocyclic bond length alternation and the twisting of the C₄ BN ring increase with the sterics of the substituents at the boron and nitrogen atoms, respectively. Regression analyses revealed that the downfield shift of the endocyclic ¹¹ B NMR resonances is linearly correlated to both the degree of twisting of the C₄ BN ring and the tilt angle of the N-substituent. Calculations indicate that the 1,2-azaborinin-1-yl ligand has no sizeable π-donor ability and that the aromaticity of the ring can be subtly tuned by the electronics of the N-substituent.

Reactivity of a Cationic Bismuth Amide towards Unsymmetric Heterocumulenes

The reactivity of a literature-known, ring-strained bismuth amide cation towards a range of unsymmetric heterocumulene substrates has been investigated. Reactions with ketenes R₂ C=C=O (R=Me, Ph), isocyanates R'N=C=O, and isothiocyanates R'N=C=S (R'=Ph, 4-CF₃ -C₆ H₄ ) proceed via facile insertion of the heterocumulene in the Bi-N bond of the cationic bismuth amide. Unexpectedly pronounced differences in the regioselectivity of these insertion reactions have been observed, yielding a rich variety of heterocycle motifs (BiC₂ NC₂ , BiC₂ NCO, BiC₂ NCS, BiC₂ NCN), some of which are unprecedented. Parameters that control the regioselectivity of the insertion reactions have been identified and are discussed based on experimental and theoretical investigations. Analytical techniques applied in this work include heteronuclear and two-dimensional NMR spectroscopy, IR spectroscopy, elemental analysis, single-crystal X-ray diffraction analyses, and DFT calculations.

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.

Sulfinyl-aminotroponiminates: alkali- (Li, Na, K) and heavy-metal (Bi) complexes

The installation of electron-withdrawing functional groups at the carbocyclic backbone of aminotroponiminate (ATI) ligands is a versatile method for influencing the electronic properties of the resulting ATI complexes. We report here Li, Na, and K salts of an ATI ligand with a phenylsulfinyl substituent in the backbone. It is demonstrated that the sulfinyl group actively contributes to the coordination chemistry of these complexes, effectively competing with neutral donor ligands such as thf or pyridine in the solid state (XRD), in solution (DOSY NMR spectroscopy), and in the gas phase (DFT). The impact of the phenylsulfinyl group on the redox properties of the complexes have been investigated and access to sodium sodiate species through ligand-induced disproportionation has been studied. Transfer of the ATI ligand to the heavy p-block element bismuth has been demonstrated. Analytical techniques applied in this work include multinuclear and DOSY NMR spectroscopy, cyclic voltammetry, DFT calculations, and single-crystal X-ray diffraction analysis.

Between imide, imidyl and nitrene – an imido iron complex in two oxidation states

Imidyl and nitrene metal species play an important role in the N-functionalisation of unreactive C–H bonds as well as the aziridination of olefines. We report on the synthesis of the trigonal imido iron complexes [Fe(NMes)L₂]^0,− (L = –N{Dipp}SiMe₃); Dipp = 2,6-diisopropyl-phenyl; Mes = (2,4,6-trimethylphenyl) via reaction of mesityl azide (MesN₃) with the linear iron precursors [FeL₂]^0,−. UV-vis-, EPR-, ⁵⁷Fe Mössbauer spectroscopy, magnetometry, and computational methods suggest for the reduced form an electronic structure as a ferromagnetically coupled iron(ii) imidyl radical, whereas oxidation leads to mixed iron(iii) imidyl and electrophilic iron(ii) nitrene character. Reactivity studies show that both complexes are capable of H atom abstraction from C–H bonds. Further, the reduced form [Fe(NMes)L₂]⁻ reacts nucleophilically with CS₂ by inserting into the imido iron bond, as well as electrophilically with CO under nitrene transfer. The neutral [Fe(NMes)L₂] complex shows enhanced electrophilic behavior as evidenced by nitrene transfer to a phosphine, yet in combination with an overall reduced reactivity.

A pair of trigonal imido iron complexes ([Fe(NMes)L₂]^0,−) in two oxidation states is reported. The anionic complex K{crypt.222}[Fe(NMes)L₂] is best described as an iron(ii) imide.

CH Activation of Cationic Bismuth Amides: Heteroaromaticity, Derivatization, and Lewis Acidity

Cationization of Bi(NPh₂)₃ has recently been reported to allow access to single- and double-CH activation reactions, followed by selective transformation of Bi-C into C-X functional groups (X = electrophile). Here we show that this approach can successfully be transferred to a range of bismuth amides with two aryl groups at the nitrogen, Bi(NR^aryl₂)₃. Exchange of one nitrogen-bound aryl group for an alkyl substituent gave the first example of a homoleptic bismuth amide with a mixed aryl/alkyl substitution pattern at the nitrogen, Bi(NPhiPr)₃. This compound is susceptible to selective N-N radical coupling in its neutral form and also undergoes selective CH activation when transformed into a cationic species. The second CH activation is blocked due to the absence of a second aryl moiety at nitrogen. The Lewis acidity of neutral bismuth amides is compared with that of cationic species "[Bi(aryl)(amide)(L)_n]⁺" and "[Bi(aryl)₂(L)_n]⁺" based on the (modified) Gutmann-Beckett method (L = tetrahydrofuran or pyridine). The heteroaromatic character of [Bi(C₆H₃R)₂NH(triflate)] compounds, which are iso-valence-electronic with anthracene, is investigated by theoretical methods. Analytical methods used in this work include nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction, mass spectrometry, and density functional theory calculations.

Two Faces of the Bi−O Bond: Photochemically and Thermally Induced Dehydrocoupling for Si−O Bond Formation

The diorgano(bismuth)alcoholate [Bi((C₆H₄CH₂)₂S)OPh] (1‐OPh) has been synthesized and fully characterized. Stoichiometric reactions, UV/Vis spectroscopy, and (TD‐)DFT calculations suggest its susceptibility to homolytic and heterolytic Bi−O bond cleavage under given reaction conditions. Using the dehydrocoupling of silanes with either TEMPO or phenol as model reactions, the catalytic competency of 1‐OPh has been investigated (TEMPO=(tetramethyl‐piperidin‐1‐yl)‐oxyl). Different reaction pathways can deliberately be addressed by applying photochemical or thermal reaction conditions and by choosing radical or closed‐shell substrates (TEMPO vs. phenol). Applied analytical techniques include NMR, UV/Vis, and EPR spectroscopy, mass spectrometry, single‐crystal X‐ray diffraction analysis, and (TD)‐DFT calculations.

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.

Aminotroponiminates: Impact of the NO2 Functional Group on Coordination, Isomerisation, and Backbone Substitution

Aminotroponiminate (ATI) ligands are a versatile class of redox-active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron-withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro-substituent in the backbone. It is demonstrated that the NO₂ group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N-binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first "naked" (i. e., without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N-coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT-)NMR spectroscopy, single-crystal X-ray diffraction analysis, and DFT calculations.

Bismuth species in the coordination sphere of transition metals: synthesis, bonding, coordination chemistry, and reactivity of molecular complexes

This contribution is focused on bismuth species in the coordination sphere of transition metals. In molecular transition metal complexes, three types of Bi-M bonding are considered, namely dative Bi→M interactions (with Bi acting as a donor), dative Bi←M interactions (with Bi acting as an acceptor) and covalent Bi-M interactions (M = transition metal). Synthetic routes to all three classes of compounds are outlined, the Bi-M bonding situation is discussed, trends in the geometric parameters and in the coordination chemistry of the compounds are addressed, and common spectroscopic properties are summarized. As an important part of this contribution, the reactivity of bismuth species in the coordination sphere of transition metal complexes in stoichiometric and catalytic reactions is highlighted.

Cationic Bismuth Aminotroponiminates: Charge Controls Redox Properties

The behavior of the redox‐active aminotroponiminate (ATI) ligand in the coordination sphere of bismuth has been investigated in neutral and cationic compounds, [Bi(ATI)₃] and [Bi(ATI)₂L_n][A] (L=neutral ligand; n=0, 1; A=counteranion). Their coordination chemistry in solution and in the solid state has been analyzed through (variable‐temperature) NMR spectroscopy, line‐shape analysis, and single‐crystal X‐ray diffraction analyses, and their Lewis acidity has been evaluated by using the Gutmann–Beckett method (and modifications thereof). Cyclic voltammetry, in combination with DFT calculations, indicates that switching between ligand‐ and metal‐centered redox events is possible by altering the charge of the compounds from 0 in neutral species to +1 in cationic compounds. This adds important facets to the rich redox chemistry of ATIs and to the redox chemistry of bismuth compounds, which is, so far, largely unexplored.

Synthesis and characterisation of boranediyl- and diboranediyl-bridged diplatinum A-frame complexes

A series of boranediyl-bridged diplatinum A-frame complexes, [Pt2X2(μ-BY)(μ-dmpm)2] (X = Cl, Br, I; Y = aryl, alkyl, amino, halo; dmpm = bis(dimethylphosphino)methane), were synthesised by the twofold oxidative addition of BX2Y to [Pt2(nbe)2(μ-dmpm)2] (nbe = norbornene) or to the paddlewheel complex [Pt2(μ-dmpm)3]. Similarly, the addition of B2X2(NMe2)2 (X = Cl, Br) to [Pt2(nbe)2(μ-dmpm)2] provided access to the diborane-1,2-diyl-bridged A-frame complexes [Pt2X2(μ-1,2-B2(NMe2)2)(μ-dmpm)2]. X-ray crystallographic studies of these (BY)n-bridged complexes show structural trends depending on the steric demands of Y and the nature of X. Analysis of higher-order 31P NMR satellites provided information on JP-Pt and JPt-Pt coupling constants, the latter correlating with the PtPt distance. All (di)boranediyl complexes also proved unstable towards (successive) loss of the bridging "BY" unit(s), resulting in the formation of [Pt2X2(μ-dmpm)2].

Bismuth Amides Mediate Facile and Highly Selective Pn-Pn Radical-Coupling Reactions (Pn=N, P, As)

The controlled release of well-defined radical species under mild conditions for subsequent use in selective reactions is an important and challenging task in synthetic chemistry. We show here that simple bismuth amide species [Bi(NAr2 )3 ] readily release aminyl radicals [NAr2 ]. at ambient temperature in solution. These reactions yield the corresponding hydrazines, Ar2 N-NAr2 , as a result of highly selective N-N coupling. The exploitation of facile homolytic Bi-Pn bond cleavage for Pn-Pn bond formation was extended to higher homologues of the pnictogens (Pn=N-As): homoleptic bismuth amides mediate the highly selective dehydrocoupling of HPnR2 to give R2 Pn-PnR2 . Analyses by NMR and EPR spectroscopy, single-crystal X-ray diffraction, and DFT calculations reveal low Bi-N homolytic bond-dissociation energies, suggest radical coupling in the coordination sphere of bismuth, and reveal electronic and steric parameters as effective tools to control these reactions.

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.

Salicylaldimines: Formation via Ring Contraction and Synthesis of Mono- and Heterobimetallic Alkali Metal Heterocubanes

The formation of salicylaldimine derivatives via ring contraction as byproducts in 2-aminotropone syntheses has been investigated. Salicylaldiminate (SAI) complexes of the alkali metals Li-K have been synthesized and transformed into heterobimetallic complexes. Important findings include an unusual double heterocubane structure of the homometallic sodium SAI, an unprecedented ligand-induced E/Z isomerization of the aldimine functional group in the homometallic potassium SAI, and the first example of a structurally authenticated mixed-metal SAI based on s-block central atoms. Rapid equilibria have been shown to play a crucial role in the solution phase chemistry of mixed-metal SAIs. Analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, VT- and DOSY NMR spectroscopy, high-resolution mass spectrometry, single-crystal X-ray diffraction analysis, and DFT calculations.

Well-Defined, Molecular Bismuth Compounds: Catalysts in Photochemically Induced Radical Dehydrocoupling Reactions

A series of diorgano(bismuth)chalcogenides, [Bi(di-aryl)EPh], has been synthesised and fully characterised (E=S, Se, Te). These molecular bismuth complexes have been exploited in homogeneous photochemically-induced radical catalysis, using the coupling of silanes with TEMPO as a model reaction (TEMPO=(tetramethyl-piperidin-1-yl)-oxyl). Their catalytic properties are complementary or superior to those of known catalysts for these coupling reactions. Catalytically competent intermediates of the reaction have been identified. Applied analytical techniques include NMR, UV/Vis, and EPR spectroscopy, mass spectrometry, single-crystal X-ray diffraction analysis, and (TD)-DFT calculations.

Molecular Bismuth Cations: Assessment of Soft Lewis Acidity

Three-coordinate cationic bismuth compounds [Bi(diaryl)(EPMe3 )][SbF6 ] have been isolated and fully characterized (diaryl=[(C6 H4 )2 C2 H2 ]2- , E=S, Se). They represent rare examples of molecular complexes with Bi⋅⋅⋅EPR3 interactions (R=monoanionic substituent). The 31 P NMR chemical shift of EPMe3 has been found to be sensitive to the formation of LA⋅⋅⋅EPMe3 Lewis acid/base interactions (LA=Lewis acid). This corresponds to a modification of the Gutmann-Beckett method and reveals information about the hardness/softness of the Lewis acid under investigation. A series of organobismuth compounds, bismuth halides, and cationic bismuth species have been investigated with this approach and compared to traditional group 13 and cationic group 14 Lewis acids. Especially cationic bismuth species have been shown to be potent soft Lewis acids that may prefer Lewis pair formation with a soft (S/Se-based) rather than a hard (O/N-based) donor. Analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, single-crystal X-ray diffraction analysis, and DFT calculations.

Methylbismuth: an organometallic bismuthinidene biradical

We report the generation, spectroscopic characterization, and computational analysis of the first free (non-stabilized) organometallic bismuthinidene, BiMe. The title compound was generated in situ from BiMe3 by controlled homolytic Bi-C bond cleavage in the gas phase. Its electronic structure was characterized by a combination of photoion mass-selected threshold photoelectron spectroscopy and DFT as well as multi-reference computations. A triplet ground state was identified and an ionization energy (IE) of 7.88 eV was experimentally determined. Methyl abstraction from BiMe3 to give [BiMe2]• is a key step in the generation of BiMe. We reaveal a bond dissociation energy of 210 ± 7 kJ mol-1, which is substantially higher than the previously accepted value. Nevertheless, the homolytic cleavage of Me-BiMe2 bonds could be achieved at moderate temperatures (60-120 °C) in the condensed phase, suggesting that [BiMe2]• and BiMe are accessible as reactive intermediates under these conditions.

Main-Group Metal Complexes in Selective Bond Formations Through Radical Pathways

Recent years have witnessed remarkable advances in radical reactions involving main-group metal complexes. This includes the isolation and detailed characterization of main-group metal radical compounds, but also the generation of highly reactive persistent or transient radical species. A rich arsenal of methods has been established that allows control over and exploitation of their unusual reactivity patterns. Thus, main-group metal compounds have entered the field of selective bond formations in controlled radical reactions. Transformations that used to be the domain of late transition-metal compounds have been realized, and unusual selectivities, high activities, as well as remarkable functional-group tolerances have been reported. Recent findings demonstrate the potential of main-group metal compounds to become standard tools of synthetic chemistry, catalysis, and materials science, when operating through radical pathways.

Combined experimental and theoretical studies towards mutual osmium-bismuth donor/acceptor bonding

Osmium(ii) PNP pincer complexes bearing a hemilabile pyridyl-pyrazolide (PyrPz) ligand have been synthesised, and their reactivity towards Lewis acidic bismuth compounds has been examined. Reactions with BiCl3 resulted in chlorine-atom-transfer to give an osmium(iii) species. Reactions with cationic bismuth species led to adduct formation through N → Bi bond formation via the PyrPz ligand. Theoretical analyses revealed that steric interactions hamper Os → Bi bond formation and indicate that such interactions are possible upon reducing the steric profile around the osmium atom. Analytical techniques include NMR, IR, and EPR spectroscopy, cyclic voltammetry, elemental analysis and DFT calculations.

Dimerization of 2-[(2-((2-aminophenyl)thio)phenyl)amino]-cyclohepta-2,4,6-trien-1-one through hydrogen bonding, C19H16N2OS

C19H16N2OS, triclinic, P1̄ (no. 2), a = 8.1510(3) Å, b = 8.8021(3) Å, c = 11.3953(5) Å, α = 72.546(2)°, β = 84.568(2)°, γ = 80.760(2)°, V = 768.86(5) Å3, Z = 2, R gt(F) = 0.0491, wR ref(F 2) = 0.1494, T = 100 K.

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.