Joachim Ballmann

Tolane-based [SCCS] pincer ligands with thioether wingtips coordinate to Ta, Mo, Re and Ru; Reduction of the Mo complexes yields two constitutional isomers of Mo–Mo-bonded dimers.

For a series of ruthenium( ii ) halide complexes pNMR spectra allowed the detection of the directly bound ³¹ P nuclei at −3900 ppm, as well as the ¹⁹ F resonance at over +3900 ppm, which are a direct probe for the sign and magnitude of A _iso .

We herein report the synthesis and characterization of a series of PNP-coordinated rhodium vinylidene complexes with a carbazole-based PNP pincer ligand framework. The availability of the reactive 14-valence electron [(PNP)RhI] complex 1 allowed a step-by-step monitoring of the metal-centered conversion of the terminal alkyne to the coordinated vinylidene. In a first step, the R–C≡CH (R = H, Ph, C6H4F, cyclohex-1-enyl) substrate oxidatively added to 1 to form an isolable corresponding alkynyl(hydrido)rhodium(III) intermediate (2a–5a), from which intramolecular conversion to the vinylidene complexes 2b–5b occurred. The equilibrium of 2a–5a with the preceding η2-π-coordinated alkyne complexes was not observed, the latter being destabilized by >5 kcal/mol as indicated by DFT modeling. This enabled easy monitoring of the vinylidene generation via a 1,3-hydrogen shift mechanism, as evidenced by kinetic measurements in combination with DFT calculations. Some aspects of the reactivity of the parent Rh=C=CH2 vinylidene complex 2b toward electrophiles and nucleophiles was investigated, uncovering a remarkable inertness of the vinylidene-rhodium unit in 2b.

KURZZUSAMMENFASSUNG: Trotz erheblicher synthetischer Bemühungen sind Alkin‐Komplexe des Technetiums im Gegensatz zu allen anderen Übergangsmetallen des d‐Blocks nicht bekannt. DFT‐Rechnungen deuten darauf hin, dass die Co‐Ligandensphäre die Stabilität solcher Verbindungen maßgeblich bestimmt und die Schwierigkeiten nicht auf spezielle Eigenschaften des Übergangsmetalls selbst zurückzuführen sind. Der arsenhaltige Tolan‐Ligand 1,2‐Bis(2‐(diisopropylarsaneyl)‐4‐(trifluormethyl)phenyl)ethin (L ^{i Pr} ) erzwingt durch das Ligandendesign eine Koordination der zentralen Alkin‐Gruppe an das Metall. Die stabilen, kristallinen Tc(III)‐ und Tc(V)‐Alkin‐Komplexe mer ‐[Tc ^III Cl ₃ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )], mer ‐[Tc ^V NX ₂ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] (X = Cl, Br) und cis,trans , mer ‐[Tc ^V N(CN)Cl(κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] wurden zusammen mit ihren Rhenium‐Homologen mer ‐[Re ^V Cl ₃ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] und mer ‐[Re ^V NCl ₂ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] dargestellt und vollständig charakterisiert. Den spektroskopischen und Dichtefunktionaltheorie (DFT) basierten Untersuchungen zufolge handelt es sich bei den Technetiumkomplexen um stabile, klassische 2e ⁻ ‐Alkin‐Komplexe, während für mer ‐[Re ^V Cl ₃ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] mit einem formal oxidierten Metallion und einem reduzierten 4e ⁻ ‐Donorliganden eine andere Situation festgestellt wurde. Dies hat eine allgemeine Bedeutung für die π‐Liganden Koordination in Gruppe 7 sowie Implikationen für benachbarte Elemente. Die erfolgreiche Übertragung auf das medizinisch relevante Kernisomer ^99m Tc belegt das Potenzial zur Verwendung von Alkin‐Gruppen als Donor‐Liganden‐Bausteine für eine stabile Chelatbildung mit Technetium auf Tracer Niveau.

Alkyne complexes are known for transition metals across the d‐block with exception of the radioelement technetium despite considerable synthetic efforts. DFT calculations suggest that this is not inherent to the transition metal but a consequence of the overall ligand sphere. The arsenic‐based tolane ligand 1,2‐bis(2‐(diisopropylarsaneyl)‐4‐(trifluoromethyl)phenyl)ethyne (L ^{i Pr} ) forces a coordination of the central alkyne moiety onto the metal through ligand design. The stable, crystalline Tc(III) and Tc(V) alkyne complexes mer ‐[Tc ^III Cl ₃ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )], mer ‐[Tc ^V NX ₂ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] (X = Cl, Br) and cis,trans , mer ‐[Tc ^V N(CN)Cl(κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] alongside their rhenium homologs mer ‐[Re ^V Cl ₃ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] and mer ‐[Re ^V NCl ₂ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] have been prepared and fully characterized. According to spectroscopic and DFT analyses, the technetium complexes represent robust, classical 2e ⁻ alkyne complexes, while a different situation was found for mer ‐[Re ^V Cl ₃ (κ ⁴ ‐ As , CC , As ‐L ^{i Pr} )] with a formally oxidized metal ion and reduced 4e ⁻ donor ligand. This has general implications for π‐ligand coordination in group 7 and potentially for neighboring elements. Successful translation to the medicinally relevant nuclear isomer ^99m Tc proves the viability of alkyne donors as building blocks for stable chelation of technetium at the tracer level.

Air-stable tetracationic P-heteropolycycles with four phosphorus atoms in the π-conjugated structure display a rich redox chemistry and photophysics.

Diphosphapentalene-derived P-heterocyclic materials with two directly fused phospholes are fairly scarce, at least in comparison to their simpler congeners containing only one phosphole entity. To fill that void, π-conjugated naphtho-fused phospholo[3,2-b]phosphole dications were prepared via in situ oxidation of the corresponding diphosphines. In the case of one specific naphtho-annulation pattern, a hitherto unprecedented bis-(Δ²-phosphetene) dication was formed selectively and isolated as a colorless powder. DFT modelling studies revealed that this bis-(Δ²-phosphetenium) salt is produced via single electron transfer steps, while all the phospholo[3,2-b]phosphole salts may either be generated via their P-diylidic counterparts or via similar radical mechanisms. Exploiting this knowledge, the dicationic phospholo[3,2-b]phosphole isomer of the bis-(Δ²-phosphetenium) salt was isolated as well. In view of the high fluorescence quantum yields of these naphtho-fused phospholo[3,2-b]phosphole salts in aqueous solution, linearly π-extended anthraceno-fused derivatives were developed in order to bathochromically shift their emissions into the biological window. While detailed optoelectronic studies confirmed our expectations, the utmost remarkable observation is that even the anthraceno-fused materials were found to be sufficiently soluble in water, despite the fact that these fluorophores comprise up to eight fused rings.

A protocol for the arylation of both N atoms in dinitrogen is presented. This protocol relies on the use of tungsten pincer complexes to split N₂ and generate tungsten nitrides, which were shown to undergo nucleophilic aromatic substitution (S_NAr) reactions with electron-deficient aryl chlorides. Starting from (¹⁵N)₂, this two-step process was exploited for the preparation of different ¹⁵N-labeled aryl amines.

We report the synthesis and structure of the novel, chiral material (S-2AH)₄[Pb₂Br₇]Br with a layered structure. Through the use of enantiomerically pure precursors, bromide-centered clusters within the non-polar, organic spacer layer are formed.