Institut für Anorganische Chemie
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The development of ligands capable of effectively stabilizing highly reactive main‐group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity‐enforced group 13–15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8‐naphthyridine (napy) core. We show that the redox‐active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element‐element interaction modes, the latter ranging from isolated, element‐centered lone pairs (e.g., E = Si, Ge) to cases where through‐space π bonds (E = Pb), element‐element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI‐E2 species as viable synthetic targets, highlighting the versatility and potential applications of napy‐based ligands in main‐group chemistry.
We investigate NCl\(_{3}\) and the NCl\(_{2}\) radical by photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The mass selected threshold photoelectron spectrum (ms-TPES) of NCl\(_{3}\) is broad and unstructured due to the large geometry change. An ionization energy of 9.7±0.1 eV is estimated from the spectrum and supported by computations. NCl2 is generated by photolysis at 213 nm from NCl\(_{3}\) and its ms-TPES shows an extended vibrational progression with a 90 meV spacing that is assigned to the symmetric N−Cl stretching mode in the cation. An adiabatic ionization energy of 9.94 ± 0.02 eV is determined.
A 1,8-naphthyridine diphosphine (NDP) reacts with boron-containing Lewis acids to generate complexes featuring a number of different naphthyridine bonding modes. When exposed to diborane B\(_{2}\)Br\(_{4}\), NDP underwent self-deprotonation to afford [NDP-B\(_{2}\)Br\(_{3}\)]Br, an unsymmetrical diborane comprised of four fused rings. The reaction of two equivalents of monoborane BBr\(_{3}\) and NDP in a non-polar solvent provided the simple phosphine-borane adduct [NDP(BBr\(_{3}\))\(_{2}\)], which then underwent intramolecular halide abstraction to furnish the salt [NDP-BBr\(_{2}\)][BBr\(_{4}\)], featuring a different coordination mode from that of [NDP-B\(_{2}\)Br\(_{3}\)]Br. Direct deprotonation of NDP by KHMDS or PhCH2K generates mono- and dipotassium reagents, respectively. The monopotassium reagent reacts with one or half an equivalent of B\(_{2}\)(NMe\(_{2}\))\(_{2}\)Cl\(_{2}\) to afford NDP-based diboranes with three or four amino substituents.
The development of complexes featuring low-valent, multiply bonded metal centers is an exciting field with several potential applications. In this work, we describe the design principles and extensive computational investigation of new organometallic platforms featuring the elusive manganese-manganese bond stabilized by experimentally realized N-heterocyclic carbenes (NHCs). By using DFT computations benchmarked against multireference calculations, as well as MO- and VB-based bonding analyses, we could disentangle the various electronic and structural effects contributing to the thermodynamic and kinetic stability, as well as the experimental feasibility, of the systems. In particular, we explored the nature of the metal-carbene interaction and the role of the ancillary η\(^{6}\) coordination to the generation of Mn\(_{2}\) systems featuring ultrashort metal-metal bonds, closed-shell singlet multiplicities, and positive adiabatic singlet-triplet gaps. Our analysis identifies two distinct classes of viable synthetic targets, whose electrostructural properties are thoroughly investigated.
Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.
The NHC-stabilised diboryne (B\(_2\)(SIDep)\(_2\); SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P−P bond activation with tetraethyldiphosphine at room temperature to form a B\(_2\)P\(_2\) heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B−B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B\(_2\)P\(_2\) rings, with their diradicaloid, planar-ring isomers lying close in energy.
The dimethylbismuth cation: entry into dative Bi-Bi bonding and unconventional methyl exchange
(2021)
The dimethyl bismuth cation, [BiMe\(_2\)(SbF\(_6\))], has been isolated and characterized. Reaction with BiMe\(_3\) allows access to the first compound featuring Bi→Bi donor–acceptor bonding. In solution, dynamic behavior with methyl exchange via an unusual S\(_E\)2 mechanism is observed, underlining the unique properties of bismuth species as soft Lewis acids with the ability to undergo reversible Bi−C bond cleavage.
Die ersten Beispiele für Lewis-Basen-Addukte des Stammboraphosphaketens H\(_{2}\)B-PCO und ihre cyclischen Dimere wurden hergestellt. Eines dieser Addukte zeigt unter milden Bedingungen eine Decarbonylierung und anschließende Insertion des Phosphinidens in die B-C-Bindung eines Borols, was in der Bildung sehr seltener Beispiele für 1,2-Phosphaborinine, B,P-Isostere von Benzol, resultiert. Die starken Donoreigenschaften dieser 1,2-Phosphaborinine wurden durch die Synthese ihrer π-Komplexe mit Metallen der Gruppe 6 bestätigt.
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.
Bei der Einelektronenreduktion eines durch eine cyclisches (Alkyl)(amino)carben (CAAC) stabilisierten Arylborylen-Carbonylkomplexes erfolgt die Bildung eines dimeren Borylketyl-Radikalanions, bedingt durch eine intramolekulare Arylmigration zum CO Kohlenstoffatom. Computergestützte Analyse liefert Hinweise auf eine radikalanionische [(CAAC)B(CO)Ar]\(^{.-}\) Zwischenstufe. Weiterführende Reduktion des entstandenen Komplexes liefert ein hoch nukleophiles (Boranyliden)methanolat.