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Methyl and methylene compounds of arsenic and antimony have been 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. Ionisation energies, vibrational frequencies and spin-orbit splittings were 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 a far lower tendency for methyl transfer for Sb(CH3)3 compared to Bi(CH3)3. This study concludes investigations on low-valent organopnictogen compounds.

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.

Dihalo bismuth cations show an unusual pentagonal bipyramidal coordination geometry with a stereochemically inactive lone pair. Their relevance for the Lewis acidity of BiX3 is discussed.

The 2‐aryl‐3,4,5,6‐tetraphenyl‐1,2‐azaborinines 1‐EMe\(_{3}\) and 2‐EMe\(_{3}\) (E=Si, Sn; aryl=Ph (1), Mes (=2,4,6‐trimethylphenyl, 2)) were synthesized by ring‐expansion of borole precursors with N\(_{3}\)EMe\(_{3}\)‐derived nitrenes. Desilylative hydrolysis of 1‐ and 2‐SiMe\(_{3}\) yielded the corresponding N‐protonated azaborinines, which were deprotonated with nBuLi or MN(SiMe\(_{3}\))\(_{2}\) (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 CO\(_{2}\) 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*=C\(_{5}\)Me\(_{5}\)), BBr\(_{2}\)Ar (Ar=Ph, Mes, 2‐thienyl), ECl\(_{3}\) (E=B, Al, Ga) and PX\(_{3}\) (X=Cl, Br) afforded the respective group 2, 13 and 15 1,2‐azaborinin‐2‐yl complexes. Salt metathesis of 1‐K with BBr\(_{3}\) 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 C\(_{4}\)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 C\(_{4}\)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.

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,...

Dibenzobismepines may be described as bismuth heterocycles containing two arene functional groups (see the graphic). The coordination chemistry of mono- and dinuclear bismepines has been investigat...

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 ¼ –N{Dipp}SiMe3); Dipp ¼ 2,6-diisopropyl-phenyl; Mes ¼ (2,4,6-trimethylphenyl) via reaction of mesityl azide (MesN3) with the linear iron precursors [FeL2]0,-. UV-vis-, EPR-, 57Fe M¨ossbauer 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.

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.

Cationic bismuth(iii) species [BiR2]+ with weakly coordinating counteranions feature two monoanionic ligands R (such as aryls, amides, alcoholates or halides), a vacant bismuth-centred p-orbital, and an occupied bismuth-centred s-orbital. The vacant orbital is available for intra- and intermolecular σ- and π-type bonding interactions and plays a crucial role in redox chemistry. The occupied s-orbital may also show minor contributions to dative bonding and is essential when addressing reversible Bi(iii)/Bi(v) redox shuttling. Variation of the anionic ligands R, the weakly coordinating counter anions, and potential neutral ligands L allows precise fine-tuning of the coordination chemistry, Lewis acidity, redox-properties, and reactivity towards nucleophiles. This contribution summarises the fundamental properties of well-defined molecular cationic bismuth compounds and highlights recent advancements in the understanding of their Lewis acidity, in their utilisation for challenging stoichometric reactions (such as CH activation and small molecule activation), and in catalytic applications (such as Lewis acid catalysis, radical polymerisation, and Bi(iii)/Bi(v) redox catalysis).

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].

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.

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., Well‐defined molecular bismuth with Bi‐EPh functional groups are catalytically active in the photochemical dehydrocoupling of silanes with TEMPO (E=S, Se, Te). Their properties are complementary or superior to those of other main group catalysts for these reactions.

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(NRaryl2)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.

The diorgano(bismuth)alcoholate [Bi((C

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 BiMe\(_3\) 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 BiMe\(_3\) to give [BiMe(_2\)]• 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–BiMe\(_2\) bonds could be achieved at moderate temperatures (60–120 °C) in the condensed phase, suggesting that [BiMe\(_2\)]• and BiMe are accessible as reactive intermediates under these conditions.

Aminotroponiminates (ATIs) have recently been shown to belong to the growing class of redox-active ligands. The choice of the metal center allowed to switch between reversible electron transfer (M=Rh) and reductively induced dimerization (M=Na). Here, we investigate if the reductively induced dimerization of ATIs is a more general phenomenon for their alkali-metal complexes. Lithium ATI complexes are shown to undergo reductively induced dimerizations, which are equilibrium reactions and chemically reversible. The choice of the metal center (Li vs. Na), the substitution pattern at the nitrogen atoms of the ATI ligands, and the solvent critically influence the regioselectivity and diastereoselectivity of the radical-dimerization reactions. Potassium ATIs are shown to be susceptible to side reactions, more specifically a reduction accompanied by hydrogen-atom transfer. Products and intermediates of the reductively induced dimerizations were characterized by techniques including NMR and EPR spectroscopy, cyclic voltammetry, DFT calculations, single-crystal X-ray diffraction, and mass spectrometry.

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., Unforeseen aspects of ATI chemistry: The impact of a nitro substituent in the backbone of the aminotroponiminate (ATI) ligand on the coordination chemistry and reactivity of alkali metal (Li−K) complexes has been investigated. This includes the first examples of i) an isolable free ATI anion, ii) E/Z imine isomerisations of ATI species and iii) N,N‐coordinated silver ATIs.

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, Ar2N−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 R2Pn−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., The first series of bismuth amides of type [Bi(NAr2)3] has been synthesized and characterized. Remarkably, they readily release aminyl radicals (NAr2). and facilitate highly selective radical coupling to give (NAr2)2. Bismuth amides mediate the selective dehydrocoupling of HPnR2 (Pn=N, P, As), including very challenging substrates. Conditions, mechanisms, and substrate scopes are complementary or superior to those of more established procedures.

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 SE2(back)‐type methyl exchange, which is, for the first time, investigated in detail for isolable, (pseudo‐)homoleptic main‐group compounds., The dimethyl bismuth cation, [BiMe2(SbF6)], has been isolated and characterized. Reaction with BiMe3 allows access to the first compound featuring Bi→Bi donor–acceptor bonding. In solution, dynamic behavior with methyl exchange via an unusual SE2 mechanism is observed, underlining the unique properties of bismuth species as soft Lewis acids with the ability to undergo reversible Bi−C bond cleavage.

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.

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)2Ln][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., Central control: A series of bismuth aminotroponiminate cations are discussed and differences between neutral and cationic compounds in terms of coordination chemistry, Lewis acidity, and redox behavior are pinpointed. Specifically, cationization allows switching from ligand‐centered redox events to metal‐centered redox events, facilitating rare examples of quasi‐reversible electron transfer at bismuth.

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

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.

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 H 2 , CO 2 , 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.

A small series of alkali metal aminotroponiminates (ATIs), [M(ATIPh/Ph)(thf)n], have been synthesized and fully characterized (M = Li, Na, K). All of these compounds adopt coordination modes that differ from those reported for derivatives with a slightly varied substitution pattern at the ATI ligand (one or two of the N-bound Ph groups substituted by iPr groups). This leads to an unprecedented ATI coordination mode for the potassium compound [K(ATIPh/Ph)] and an unusual Li···Ph interaction for the lithium compound [Li(ATIPh/Ph)]. The influence of the substitution pattern at the ATI ligand on the shape and energy of the frontier orbitals of its sodium complexes has been rationalized by theoretical methods and correlated with experimental results. Analytical techniques applied in this work include NMR spectroscopy, single crystal X-ray diffraction, and DFT calculations.

Well-defined cationic bismuth complexes, [Bi(NR2)Ln]+, based on simple, monodentate, monoanionic amide ligands have recently been reported (R = Me, iPr, etc.). The unusual reactivity patterns of these species are highlighted, with a focus on a recently reported double CH activation reaction. Mechanistic aspects and the impact of charge on reactivity are discussed. These results are compared with literature-known strategies in bismuth-mediated CH activations, and their potential implications for future research in the field are outlined.1 Introduction2 Bismuth-Mediated CH Activation3 Cationic Bismuth Complexes4 Cationic Bismuth Amides for CH Activation5 Conclusion

A straightforward synthetic route to aminotroponate (AT) and aminotroponiminate (ATI) ligands with a ferrocenyl substituent at nitrogen is presented. Sodium derivatives have been synthesised and the first synthetic access to bismuth AT and ATI species has been demonstrated. All compounds show reversible ligand-centered redox events under oxidising conditions. In a homoleptic bismuth ATI complex, weak electronic communication between three ATI ligands was observed. The coordination chemistry and redox properties of AT and ATI compounds have been investigated by methods including NMR and UV/vis spectroscopy, single-crystal X-ray diffraction, cyclic voltammetry, and DFT calculations.

Three‐coordinate cationic bismuth compounds [Bi(diaryl)(EPMe3)][SbF6] have been isolated and fully characterized (diaryl=[(C6H4)2C2H2]2−, E=S, Se). They represent rare examples of molecular complexes with Bi⋅⋅⋅EPR3 interactions (R=monoanionic substituent). The 31P 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., Cationic bismuth species [Bi(diaryl)]+ show significant bonding interactions with soft donors EPMe3 (E=S, Se). The 31P NMR chemical shifts of EPMe3 are sensitive to Lewis pair formation and are suggested as an easily accessible experimental parameter for the evaluation of the soft character of a Lewis acid. Using this method, a range of neutral and cationic bismuth species have been investigated and compared to more traditional group 13 and 14 Lewis acids.

Bismepines are 3-fold unsaturated seven-membered rings containing one bismuth atom. A set of dibenzobismepine complexes have been synthesized and isolated, among them a dinuclear bismepine, halobismepines, and cationic bismepines. They were investigated with respect to the structural properties, olefin-bismuth interactions, heteroaromaticity, and Lewis acidity (including a comparison with a range of simple bismuth and group 13 Lewis acids). Applied analytical techniques include NMR spectroscopy, single-crystal X-ray analysis, elemental analysis, and density functional theory calculations.

The controlled radical chemistry of bismuth compounds is still in its infancy. Further developments are fueled by the properties of these complexes (e.g., low toxicity, high functional group tolerance, low homolytic bond dissociation energies, and reversible homolytic bond dissociations), which are highly attractive for applications in synthetic chemistry. Here we report the first catalytic application of transition metal bismuthanes (i.e. compounds with a Bi-TM bond; TM=transition metal). Using the catalyzed radical cyclo-isomerization of δ-iodo-olefins as a model reaction, characteristics complementary or superior to known B, Mn, Cu, Zn, Sn, and alkali metal reagents are demonstrated (including a different crucial intermediate), establishing transition metal bismuthanes as a new class of (pre-)catalysts for controlled radical reactions.

Ungesattigte Brucken, die in gespannten ansa-Metallocenen zwei Cyclopentadienyl-Einheiten miteinander verbinden, sind auserst selten und auf Kohlenstoff-Kohlenstoff-Doppelbindungen beschrankt. Die Synthese und Isolierung eines gespannten Ferrocenophans mit einer ungesattigten Brucke aus zwei Boratomen, die isoelektronisch mit einer C=C-Doppelbindung ist, wurde durch Reduktion eines carbenstabilisierten 1,1′-Bis(dihalogenboryl)ferrocens erstmals verwirklicht. Spektroskopische und elektrochemische Messmethoden sowie DFT-Rechnungen wurden angewendet, um den Einfluss der beispiellosen, gespannten cis-Konfiguration auf die optischen und elektrochemischen Eigenschaften der carbenstabilisierten Diboren-Einheit zu untersuchen. Erste Reaktivitatsstudien zeigen, dass das Dibora[2]ferrocenophan anfallig fur die Spaltung der Bor-Bor-Doppelbindung ist.

The synthetic access to cationic bismuth compounds based on simple, monodentate, synthetically useful amido ligands, [Bi(NR2)2(L)n]+, has been investigated (R = Me, iPr, Ph; L = neutral ligand). With [BPh4]- as a counteranion, the formation of contact ion pairs and subsequent phenyl transfer from B to Bi is observed. An intermediate of this reaction, [Bi(NMe2)2(HNMe2)(BPh4)] (1), could be isolated and fully characterized. The use of fluorinated tetrarylborates as counteranions leads to more stable cationic bismuth amides. The solvent-separated ion pairs [Bi2(μ2-NMe2)2(NMe2)2(thf)6]2+ (4) and [Bi(NiPr2)2(thf)3]+ (5) were fully characterized with [B(3,5-C6H3(CF3)2)4]- anions balancing the positive charge. The coordination chemistry, aggregation in solution, and spectroscopic features of these compounds were investigated. Compounds 4 and 5 show an increased reactivity towards diisopropylcarbodiimide compared to their neutral parent compounds. These reactions result in formation of the first cationic bismuth guanidinates. Characterization techniques include 1H, 11B, 13C, 15N, 19F and 31P (VT-)NMR and IR spectroscopy, single crystal X-ray diffraction analysis, and DFT calculations.

The coordination chemistry of alkalimetal aminotroponiminates (ATIs) was investigated based on (i) a lithium ATI, (ii) the first example of a sodium ATI, and (iii) the first example of a structurally characterized potassium ATI. In the lithium derivative of this series, the ATI ligand adopts a well-known κ2N binding mode. In contrast, the sodium and potassium ATIs show two different types of unprecedented polymeric structures in the solid state, unraveling a surprisingly rich coordination chemistry for the ATI ligand family. In the solid-state structure of the potassium compound, ATI ligands bridge the metal atoms in a μ2-κ2N binding mode. The sodium compound reveals a μ2-κ2Nκ5C coordination mode with an unusual interaction of a metal center with a C7 ATI ligand backbone. NMR studies suggest that this type of interaction might also be accessible in solution. It was further studied by DFT calculations. The tendency of monoanionic ATI ligands to interact with transition-metal centers via their C7 ligand bac...