Hans_Bauer96

Mn(N,N′) systems can do it! Complexes combining Earth-abundant manganese and an economically attractive, phosphine-free pyridinium amidate ligand catalyze the dehydrogenation of formic acid to release H₂ selectively, thus providing access to a catalytic system for hydrogen release from a liquid organic hydrogen carrier with turnover frequencies exceeding 1000 h⁻¹.

ABSTRACT

Formic acid is a promising hydrogen carrier. Herein, we synthesized and profiled a series of manganese-based complexes containing a quinoline-pyridinium amidate N,N′-bidentate coordinating ligand, MnX(CO)₃(N,N’), for catalytic formic acid dehydrogenation. The activity of these novel manganese complexes was dependent on the metal-bound halide as well as the motif of the donor-flexible pyridinium amidate ligand. The ortho′-methylated ortho-pyridinium amidate system Mn3 showed highest activity and reached up to 400 turnovers and a turnover frequency of 1100 h⁻¹. Modification of the catalytic conditions unveiled the importance of the water concentration and a direct temperature dependence, with a large activation enthalpy (ΔH^‡ = 99 kJ mol⁻¹) and a close to zero activation entropy (ΔS^‡ = –37 J K⁻¹ mol⁻¹). Mechanistic investigation further suggest that the process is homogeneous, and that the turnover-limiting step is the β–hydride elimination of formate from a catalytically active species that comprises both the halide and the PYA ligand bound to the manganese center.

A series of structurally and electronically diverse phosphoranylideneketenes (R₃PCCO) and phosphoranylidenethioketenes (R₃PCCS) were synthesized and comprehensively characterized by single-crystal X-ray-crystallography, ¹³C NMR, and IR spectroscopy. Despite acting as relatively weak ambidentate Lewis donors, these compounds readily form stable adducts with strong Lewis acids.

Abstract

Posphoranylideneketene Ph₃PCCO and its sulfur analogue, Ph₃PCCS, are cumulated ylides that exhibit diverse reactivity and distinct structural features. Herein, we present the first systematic study of substituent effects on the structures and bonding of a series of aryl- and alkyl-substituted phosphoranylideneketenes, R₃PCCO [R = Et, cyclohexyl, NMe₂, 4-Me₂N-C₆H₄, 4-MeO-C₆H₄, 4-CF₃-C₆H₄, 3,5-(CF₃)₂-C₆H₃], prepared from the corresponding phosphonium salts, [R₃PCH₂COOEt]X (X = Br, I) and two equivalents of Na[N(SiMe₃)₂]. Multinuclear NMR and IR spectroscopy, supported by single-crystal X-ray diffraction, revealed that the bond strength within the central P═C═C═O fragment increases with the electron-deficiency of the aryl substituents at phosphorus. The corresponding phosphoranylidenethioketenes, R₃PCCS (R = Et, cyclohexyl, NMe₂, 4-Me₂N-C₆H₄, 4-MeO-C₆H₄, 4-CF₃-C₆H₄), were obtained by reactions of R₃PCCO with CS₂. The rate of conversion of R₃PCCO into R₃PCCS decreases with increasing electron deficiency at phosphorus. Both R₃PCCO and R₃PCCS act as relatively weak ambidentate Lewis donors, yet they form stable acid-base adducts with strong Lewis acids such as B(C₆F₅)₃ and Al(C₆F₅)₃.

Reactions of the doubly reduced distannynes, [Ar′SnSnAr′M₂], (Ar′ = C₆H₃-2,6-Dipp; M ═ ′Li, Na, K), with the successively heavier alkali metals (M) result in reduction of M, which is proposed to occur via a suitably disposed π* SOMO of the putative radical anions, [Ar′SnSnAr′M₂]^•−.

Abstract

Reactions of the doubly reduced distannynes, [Ar′SnSnAr′M₂], (Ar′ = C₆H₃-2,6-Dipp; M = Li, Na, K), with the successively heavier group 1 elements (M′) result in reduction of M and the isolation of [Ar′SnSnAr′M′₂]. Although the viability of these observations, along with the reversible formation of [Ar′SnSnAr′K₂] by treatment of [Ar′SnSnAr′Rb₂] with potassium, is successfully predicted by a combined theoretical and thermochemical analysis, assessment of the bonding within [Ar′SnSnAr′M₂] suggests that any M⁺ ns valence orbital contribution should be too high in energy to effect M⁺ reduction. Based on a consideration of the Sn─Sn π bonding and theoretical assessment of the resultant frontier orbitals, however, we suggest that the electron transfer necessary for M⁺ reduction, occurs intramolecularly and via a suitably disposed π* SOMO of the putative radical anions, [Ar′SnSnAr′M₂]^•−.

Das Methylbismut-Dikation wurde mithilfe von lediglich fünf substitutionslabilen THF-Liganden gebildet [BiMe(thf)₅]²⁺. Die sechsfach koordinierte Verbindung zeigt eine ungewöhnliche pentagonal pyramidale Koordinationsgeometrie. Präzedenzlose Lewis-acide und Lewis-superacide Eigenschaften wurden durch Ausnutzung der Koordinationschemie von “BiMe²⁺” und der Substitutionslabilität der THF-Liganden gefunden.

Zusammenfassung

Ein grundlegendes Verständnis der natürlich bevorzugten Koordinationsgeometrie von Molekülkomplexen bildet die Grundlage, um deren physiko-chemische Eigenschaften und Reaktivität zu rationalisieren, vorherzusagen und zu gestalten. In dieser Hinsicht ist es eine zentrale Herausforderung, Verbindungen mit ungewöhnlicher Koordinationsgeometrie darzustellen und ein grundlegendes Verständnis ihrer Eigenschaften zu entwickeln. Die Untersuchung dieser Fragestellungen verspricht eine innovative Expansion des chemischen Raums und das Offenlegen von Reaktivitäten, die für Verbindungen in klassischen Koordinationsgeometrien nicht zugänglich sind. Hier präsentieren wir die Synthese, Isolierung und Charakterisierung des einfachsten Organobismut-Dikations, des Methylbismut-Dikations [BiMe(thf)₅][SbF₆]₂ (1), welches lediglich von fünf substitutionslabilen THF-Liganden stabilisiert wird. Die sechsfach koordinierte Verbindung zeigt eine seltene, pentagonal pyramidale Koordinationsgeometrie um das Zentralatom, was äußerst ungewöhnlich ist, da es sich um eine Organometallverbindung handelt, bei der lediglich einzähnige und einfach anionische bzw. neutrale Liganden ohne besonderen sterischen Anspruch eingesetzt werden. Die detaillierte Untersuchung dieser Verbindung mit experimentellen und theoretischen Methoden erklärt die Ursache dieser ungewöhnlichen Koordinationsgeometrie und offenbart mehrere Lewis-acide Koordinationsstellen sowie Ligand-induzierte Lewis-Superacidität.

Es wird eine neue Klasse an chelatisierenden Diazoalkenen vorgestellt und ihre Koordinationskomplexe mit Pd und Pt charakterisiert. Durch Bestrahlung wird ein N₂-Verlust erzeugt, wodurch erstmals spektroskopisch charakterisierte Triplet-Metallovinylidene unter Verwendung von FD-FT-THz-EPR-Spektroskopie und SQUID-Messungen nachgewiesen werden. Die Struktur wird durch in-crystallo Röntgenbeugung verifiziert, während computergestützte Studien die einzigartige Bindung der neuen Diradikalklasse bestätigen.

Kurzzusammenfassung

Triplett-Carbene mit einem Metallsubstituenten neben dem Carbenzentrum (Metallocarbene; R−C−M) bilden eine neue Klasse von Diradikalen auf dem Gebiet der reaktiven Intermediate. Hier berichten wir über die Synthese der ersten spektroskopisch charakterisierten Triplett-Metallovinylidene (R−C→M; M = Pt, Pd). Der synthetische Zugang basiert auf einem starren P/C-chelatisierenden Diazoalkenliganden und dessen Koordination an Pt und Pd. Der C/P-chelatisierende Ligand schränkt den R−C→M-Winkel geometrisch ein und verhindert eine freie Biegung. Die Bestrahlung des freien Diazoalkenliganden erzeugt ein Triplett-Vinyliden, das durch Q-Band-Elektronenspinresonanzspektroskopie (EPR) charakterisiert wird. Die Bestrahlung der Metallkoordinationskomplexe (Pt und Pd) führt zu Triplett-Metallovinylidenen, die bei niedrigen Temperaturen charakterisiert wurden, einschließlich Röntgenbeugung des im Kristall bestrahlten Reaktionsproduktes. Kombinierte FD-FT-THz-EPR-Spektroskopie und SQUID-Messungen ermöglichten die Bestimmung der großen Triplett-Nullfeldaufspaltung (ZFS) mit D-Werten von 124.5 cm⁻¹ (Pt) und 8.0 cm⁻¹ (Pd), die hervorragend mit der durch quantenchemische Berechnungen erhaltenen elektronischen Struktur übereinstimmen.

Despite its notorious reputation as a war gas, phosgene (COCl2${\rm COCl}_2$) is one of the most important intermediate chemicals in industry. In this study, we present the crystal structures of two phosgene polymorphs as deduced from powder neutron diffraction and show which intermolecular interactions stabilise the different modifications. The first inelastic neutron scattering spectra show an unusual separation of the translational and librational modes, alongside sharp bands for the internal modes.

Abstract

The crystal structures of α$\alpha$- and β$\beta$-phosgene have been elucidated on the basis of variable temperature neutron powder diffraction. Although the stable α$\alpha$-phase closely mirrors the published structure (I41/a$I4_1/a$, No. 88), the new metastable β$\beta$-phase crystallises in Cmc21$Cmc2_1$ (No. 36, at 135 K: a = 10.244042(22) Å, b = 6.280321(21) Å, c = 5.46069(4) Å). Both modifications show dipole–dipole interactions, but only α$\alpha$-phosgene shows pronounced σ$\sigma$-hole interactions. Quantum chemical calculations in both solid state and of model dimers in gas-phase reveal a complex interplay of intermolecular interactions. The first inelastic neutron scattering spectra of α$\alpha$-phosgene shows an unusual separation of the translational and librational modes, alongside sharp bands for the internal modes. Our computational studies also show an unusual, extensive mixing of the in-phase C–Cl stretch (ν2$\nu _2$) and the out-of-plane bend (ν6$\nu _6$) modes, which are symmetry-forbidden from mixing in the gas-phase.

Katalysatoren, die aus dem halogenverbrückten Methylnaphthyl-Palladium-Dimer [Pd(1-MeNAP)Br]₂ und Biarylphosphin-Liganden in Kombination mit der Base LiHMDS generiert werden, katalysieren Buchwald-Hartwig-artige Aminierungen und para-C–H-Arylierungen von nicht-aktivierten Arylfluoriden bereits bei 60 °C. Ihre hohe Leistungsfähigkeit wird der effizienten Generierung monoligierter Pd(0)-Spezies zugeschrieben.

Zusammenfassung

Die C–F-Bindung gehört zu den stärksten Bindungen in organischen Molekülen und kann nur durch wenige Übergangsmetallkatalysatoren unter rauen Bedingungen oder in Kupplungen mit hochreaktiven Nukleophilen gespalten werden. Ein Methylnaphthyl (MeNAP)-Palladiumbromid/BrettPhos-Katalysator mit Lithiumbis(trimethylsilyl)amid (LiHMDS) als Base ermöglicht die Aminierung von nicht aktivierten Arylfluoriden unter Erzeugung von primären, sekundären und tertiären Anilinen bereits bei 40–60 °C. Ein verwandtes Katalysatorsystem ermöglicht zudem die para-C–H-Arylierung von tritylierten Anilinen mit Arylfluoriden unter Bildung von Biarylaminen.

A series of frustrated Lewis pair (FLP) stabilized arsenic compounds with formal oxidation numbers at As of +1, 0, and −1 are presented. A stable FLP-chelated complex of As₂ was prepared which undergoes the light-induced release of nascent diarsenic, As₂ ^nasc, which reveals clean triple-bond type reactivity with dienes and metal-metal bonds under mild conditions .

Abstract

The first examples of frustrated Lewis pair (FLP)-stabilized compounds with formal oxidation states of arsenic ranging from −1 to +1 have been synthesized. These chelates include the metalated arsinidenyl As(─I) anion in FLP{As─K} (1), which provides access to the parent FLP-stabilized arsinidene, As(+I)─H, in FLP{As─H} (3), and a diatomic arsenic(0) allotrope within FLP{As─As}FLP (5). Irradiation of the As₂ complex 5 represents an unprecedented method for the generation of nascent diarsenic, As₂ ^nasc , which shows triple-bond like reactivity with a diene and selective As₂ unit insertion into metal-metal bonds under mild conditions.

Ferrocene-based N-heterocyclic tetrylenes [Fe{(η⁵-C₅H₄)NBTrip₂}₂E](E = GePb; Trip = C₆H₂-2,4,6-iPr₃)exhibit long EN and short BN bonds, in agreement with increased electrophilicity due to the -M effect of the N-substituents, whose stericdemand prevents coordination of 4-(dimethylamino)pyridine (DMAP) to theplumbylene Pb^II atom, but allows the reaction with the smallnucleophile NH₃.

The diaminoferrocene derivative fc[NH(BTrip₂)]₂ (1H₂; fc = 1,1′-ferrocenylene, Trip = 2,4,6-triisopropylphenyl) was prepared from fc(NH₂)₂ and Trip₂BF and used for the preparation of the N-heterocyclic tetrylenes fc{[N(BTrip₂)]₂E} (1E, E = Ge, Sn, Pb) via the TMEDA-coordinated lithium amide 1Li₂(TMEDA)₂ (TMEDA = N,N,N′,N′-tetramethylethylenediamine). The N-heterocyclic plumbylene fc{[N(BMes₂)]₂Pb} (2, Mes = mesityl), which was obtained analogously, reacts with 4-(dimethylamino)pyridine (DMAP) to afford the adduct fc{N(BMes₂)]₂Pb(DMAP)} (3). No reaction with DMAP was observed with the sterically more congested plumbylene 1Pb. 1Pb and 2 both undergo immediate ammonolysis with NH₃. All new compounds were structurally characterised by single-crystal X-ray diffraction.

A T-shaped Bi(III) trisamide featuring a sterically demanding NNN pincer ligand was prepared. The planarization of the Bi center furnishes a lowest unoccupied molecular orbital with distinct Bi(6p) orbital character which unlocks clean one-electron reduction to afford a crystalline Bi(II) radical anion. Comprehensive spectroscopic analysis reveals the localization of the unpaired electron at the bismuth center further confirmed by reactivity studies.

Abstract

We report the synthesis of a planarized tris-amidobismuthane supported by a rigid, bulky NNN pincer ligand, which enforces a T-shaped geometry at the bismuth center. The Bi(NNN) complex features a low-lying LUMO with distinct Bi(6p) orbital character as shown by DFT calculations. Cyclic voltammetry reveals a fully reversible one-electron reduction at E _1/2 = –1.85 V versus Fc^0/+ in THF. Chemical reduction with KC₈ in the presence of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (222-crypt) enables the isolation of an unprecedented Bi(II) radical anion in high isolated yields. Multi-frequency EPR, X-ray absorption spectroscopy and SQUID magnetometry complemented by theoretical calculations confirm localization of the unpaired electron on the bismuth center. Preliminary reactivity studies display radical reactivity as shown by single-electron transfer chemistry and radical coupling reactions.

Aluminum–silicon adducts of NHC-phosphinidenides are synthesized and structurally characterized. Their bonding and electronic structures are compared with those of isosteric NHC-disilylsilylene complexes by DFT, NBO, and QTAIM analyses, highlighting the interplay of covalent versus coordinative interactions and emphasizing the significance of isosterism in main-group chemistry.

Aluminum-silicon adducts of N-heterocyclic carbene (NHC) phosphinidenides have been synthesized and structurally characterized. Their bonding and electronic structures were compared with those of isosteric NHC-disilylsilylene complexes using DFT, NBO, and QTAIM analyses. The results reveal striking structural analogies, in particular similar pyramidalization at the exocyclic main-group center, while also highlighting clear differences between the covalent SiSi and PSi bonds and the more polar, coordinative P–Al interaction. Extension to an arsenic analog further underlines the generality of this approach and emphasizes the significance of isosterism as a guiding principle in main-group organometallic chemistry.

C–H functionalisation and ether cleavage are typically performed by aggressive organolithium reagents. Unveiling the untapped Brønsted basicity of magnesium-oxo species, the reaction of Mg(I) precursors with epoxides initially proceeds via deoxygenation, followed by deprotonation and rearrangement of a second epoxide. Episulfides form a bridged chalcogen species initially, but ultimately show divergent reactivity to the disulfide-bridged product.

Abstract

Chemical C–H functionalisation is traditionally the domain of potent organolithium bases that require cryogenic conditions, whereas biologically inspired C–H functionalisation can be executed by transition metal-oxo species. Blending these chemical and biological approaches, this work exploits magnesium-oxo complexes for selective C–H deprotonation at ambient temperature. Overall, three low valent magnesium(I) dimers, [^DippNacnacMg]₂ 1, [^DepNacnacMg]₂ 2 and [^MesNacnacMg]₂ 3, react with two equivalents of propylene oxide to generate dinuclear Mg complexes of general formula [NacnacMg(OH)(OCH₂CHCH₂)MgNacnac] (Nacnac = HC(C(CH₃)NAr)₂). Isolation of oxo-bridged [^DippNacnacMg-O-Mg^DippNacnac] coupled with deuterium labeling studies shows that the reaction proceeds via epoxide deoxygenation, followed by deprotonation and rearrangement of a second equivalent of the epoxide to generate the alkoxide. A range of terminal and internal epoxides was investigated (propylene oxide, butylene oxide, isobutylene oxide, and cyclohexene oxide). The β-C-H position was selectively deprotonated in each case, as confirmed by NMR spectroscopy and X-ray diffraction studies. Exchanging epoxides for episulfides instead generated disulfide-bridged species, showcasing the difference in Brønsted basicity between Mg-O and Mg-S functional groups. Overall, this work demonstrates the unharnessed potential of main group metal-oxo complexes for selective C–H deprotonation.

We present the organometallic first-step carbolithiation products of anionic styrene polymerization with diethyl ether and thf, that have not been isolated so far due to the high reactivity of anionic polymerization. X-ray solid-state and NMR solution-state experiments show different intermediates in the different solvents. in situ FT-IR and DFT-calculations present mechanistic proposals for the initiation reaction.

Kurzzusammenfassung

Die anionische Polymerisation hat sich in den letzten 70 Jahren zu einer der am häufigsten verwendeten Polymerisationstechniken sowohl in der Industrie als auch im akademischen Bereich entwickelt. Aufgrund der erforderlichen hohen Reaktivität der Polymerisation war es bisher nicht möglich, das metallorganische Zwischenprodukt zwischen Initiierungs- und Propagationsschritt zu isolieren, ebenso ist der Mechanismus der anionischen Polymerisation noch nicht vollständig verstanden. Darüber hinaus stellen Deprotonierungen in benzylischen Positionen nach wie vor eine Herausforderung dar, was zwar die Voraussetzung für eine erfolgreiche lebende carbanionische Polymerisation ist, aber auch den synthetischen Zugang zu den Zwischenprodukten erschwert. In diesem Artikel stellen wir die Synthese und Isolierung des Carbolithierungsproduktes der ersten Stufe der anionischen Styrolpolymerisation in Diethylether und Tetrahydrofuran vor. Charakterisierungen im Festkörper durch Röntgenbeugung und in Lösung durch ausgedehnte NMR-Experimente wurden durchgeführt. Unterschiedliche Initiationsreaktivitäten wurden durch in situ FT-IR-Spektroskopie beobachtet, sodass gezeigt werden konnte, dass die Intermediate für die Polymerisationsreaktivität verantwortlich sind. Eine mögliche mechanistische Erklärung für die Initiationsschritte wurde durch DFT-Berechnungen präsentiert. Durch unseren Ansatz, die kettenrelevanten Zwischenstufen auf molekularer Ebene zu isolieren, konnten wir neue Erkenntnisse über den bestehenden Mechanismus gewinnen.

A new phosphenium dication [P(μ-NTer)₂P–hexyl–P(μ-NTer)₂P]²⁺ was synthesized and fully characterized starting from a p-Centered biradical.

Starting from the biradicaloid [·P(μ-NTer)₂P·] (Ter = 2,6-dimesitylphenyl), the addition of ethyl bromide yields the addition product [Et–P(μ-NTer)₂P–Br]. Using 1,6-dibromohexane, the corresponding hexyl-bridged species [Br–P(μ-NTer)₂P–hexyl–P(μ-NTer)₂P–Br] is formed. The addition of one or two equivalents of a strong Lewis acid such as GaCl₃ leads to the abstraction of the bromide, forming the monocation [Et–P(μ-NTer)₂P]⁺ or the dication [P(μ-NTer)₂P–hexyl–P(μ-NTer)₂P]²⁺, respectively. Both new salts with the cyclic aminophosphenium cations are fully characterized, and their structure and bonding are discussed.

From solutions of LiClO₄ and crown ethers, three new salts with crown-ether-encapsulated Li⁺ cations and perchlorate anions are obtained. Their structures and thermal and conductivity data of one example are described.

Extensive scientific research is currently carried out globally to improve the performance of rechargeable batteries based on lithium ions and to develop new, especially solid-state battery systems. Herein, results of preparative investigations of Li[ClO₄] with crown ethers of different ring sizes are presented. The three new coordination compounds [Li₂(12cr4)₃][ClO₄]₂, [Li(15cr5)(acetone)][ClO₄], and [Li(dibenzo-18cr6)(H₂O)₂][ClO₄] are prepared in crystalline purity and high yield. The crystal and molecular structures are determined by single-crystal X-ray diffraction. In addition, the already known structure of [Li(18cr6)(H₂O)₂][ClO₄] is redetermined and confirmed. They all consist of discrete molecular cations in which Li⁺ is encapsulated in the respective crown ether ring and perchlorate anions. In all four compounds, the coordination environment of the Li⁺ ion contains besides O atoms of the crown ether molecules addition donors, i.e., an O atom of an empty 12cr4 ring, the O atom of an acetone molecules or those of water molecules. Thermal investigations reveal melting points around 100 °C. The measurement of the electrical conductivity of [Li₂(12cr4)₃][ClO₄]₂ gives a value of 3.5 ×10⁻⁶ S/cm, which is ≈1000 times smaller than that of currently used Li-based electrolytes.