Frontispiece: Cationic Tetrylene-Iron(0) Complexes: Access Points for Cooperative,Reversible Bond Activation and Open-Shell Iron(−I) Ferrato-Tetrylenes

The open-shell cationic stannylene-iron(0) complex 4 ( 4 =[^PhiPDippSn⋅Fe⋅IPr]⁺; ^PhiPDipp={[Ph₂PCH₂Si(ⁱPr)₂](Dipp)N}; Dipp=2,6-ⁱPr₂C₆H₃; IPr=[(Dipp)NC(H)]₂C:) cooperatively and reversibly cleaves dihydrogen at the Sn−Fe interface under mild conditions (1.5 bar, 298 K), in forming bridging hydrido-complex 6 . The One-electron oreduction of the related Ge^II−Fe⁰ complex 3 leads to oxidative addition of one C−P linkage of the ^PhiPDipp ligand in an intermediary Fe^−I complex, leading to Fe^I phosphide species 7 . One-electron reduction reaction of 4 gives access to the iron(−I) ferrato-stannylene, 8 , giving evidence for the transient formation of such a species in the reduction of 3 . The covalently bound tin(II)-iron(−I) compound 8 has been characterised through EPR spectroscopy, SQUID magnetometry, and supporting computational analysis, which strongly indicate a high localization of electron spin density at Fe^−I in this unique d⁹-iron complex.     

On the Reactivity of Phosphaalumenes towards C−C Multiple Bonds

Heterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems. With sterically demanding alkynes 1,2-phosphaalumetes were afforded, whereas the reaction with HCCH or HCCSiMe₃ gave 1,4-phosphaaluminabarrelenes. Using styrene saturated 1,2-phosphaalumates were formed, which reacted further with additional styrene to give different regio-isomers of 1,4-aluminaphosphorinanes. Using ethylene, a 1,4-aluminaphosphorinane is obtained, while with 1,3-butadiene a bicyclic system containing an aluminacyclopentane and a phosphirane unit was synthesized. The experimental work is supported by theoretical studies to shed light on the mechanism governing the formation of these heterocycles.     

Substrates and Cyclic Peptide Inhibitors of the Oligonucleotide-Activated Sirtuin 7**

The sirtuins are NAD⁺-dependent lysine deacylases, comprising seven isoforms (SIRT1–7) in humans, which are involved in the regulation of a plethora of biological processes, including gene expression and metabolism. The sirtuins share a common hydrolytic mechanism but display preferences for different ϵ-N-acyllysine substrates. SIRT7 deacetylates targets in nuclei and nucleoli but remains one of the lesser studied of the seven isoforms, in part due to a lack of chemical tools to specifically probe SIRT7 activity. Here we expressed SIRT7 and, using small-angle X-ray scattering, reveal SIRT7 to be a monomeric enzyme with a low degree of globular flexibility in solution. We developed a fluorogenic assay for investigation of the substrate preferences of SIRT7 and to evaluate compounds that modulate its activity. We report several mechanism-based SIRT7 inhibitors as well as de novo cyclic peptide inhibitors selected from mRNA-display library screening that exhibit selectivity for SIRT7 over other sirtuin isoforms, stabilize SIRT7 in cells, and cause an increase in the acetylation of H3 K18.     

Nitraza-/Oxa-Propylene- and Hydrazonemethylene-Bridged 1,2,4-Nitraminotriazoles and Selected Salts

Two new bridged nitraminotriazoles with bridging oxapropylene and nitrazapropylene moieties were synthesized, and converted into several salts, as well as from the hydrazonemethylene bridged nitraminotriazole. All compounds were fully characterized by NMR and IR spectroscopy, elemental analysis as well as differential thermal analysis. The sensitivity towards friction and impact were determined according to BAM standard technics and the energetic properties were calculated by using the EXPLO5 computer code. The neutral compounds as well as the various salts were examined in terms of their physicochemical properties and detonation performance to each other and compared to the commonly used secondary explosive RDX.     

Triethylamine-Mediated Transformation of Phosphonates into Phosphonamidates

Organophosphorus compounds such as phosphonamidates are gaining attention across different fields of chemistry, with interesting applications as pharmaceuticals, or pesticides. However, practical application of phosphonamidates is complicated by their difficult syntheses which often involve expensive or unstraightforward reagents and harsh conditions. To remedy these issues, we present a flexible, room temperature synthesis for novel P-alkylphosphonamidates without the need for intermediary purification. Commonly available phosphonates are first chlorinated by use of oxalyl chloride and phosphonylaminium salts are used to mediate the harsh reactivity of phosphonochloridates, giving rise to the desired products. We demonstrate the compatibility of our protocol with primary and secondary amines, as well as with different phosphonate esters. The proposed pathway also enables the synthesis of primary phosphonamidates using ammonium acetate as a cheap and safe alternative for ammonia. In future research, this protocol will also enable the synthesis of bioactive targets that are incompatible with current protocols.     

Cover Feature: Copper and Nickel Complexes of Oxamate−Phenol Containing Ligands: A Structural Dichotomy in Oxidized Species (Eur. J. Inorg. Chem. 15/2023)

The copper and nickel complexes of two tetradentate ligands derived from bis(aminophenol) and bis(phenol) architectures connected by an oxamate linker were isolated. Depending on the metal and ligand, the complex is isolated with either an intact (deprotonated) ligand ( 1²⁻ ), one-electron oxidized ligand ( 2⁻ ) or quinone form ( 3 ). Surprisingly, the Mannich base is easier to oxidize than the amidophenol derivatives. The complexes were characterized by X-ray diffraction, cyclic voltammetry, UV-Vis-NIR and EPR spectroscopies. Complex 1 shows two reversible oxidation waves assigned to the successive iminosemiquinone/aminophenolate redox systems. Complex 2⁻ shows an intense NIR feature, as well as an EPR signal at g_iso=2.043, consistent with a metallic contribution to the main ligand radical SOMO. Complex 3 shows the typical feature of an isolated Cu(II) complex. Spectro-electrochemistry coupled to DFT calculations demonstrate a ligand-centered oxidative redox chemistry for all the complexes.     

Investigations on Novel 1,3-Diazetidine Based Four-Membered N-Heterocyclic Carbenes

Attempts towards the synthesis of two novel four-membered 1,3-diazetidine based N-heterocyclic carbenes (NHCs) containing an organic backbone with a carbonyl functionality were undertaken. These carbenes cannot be isolated but the respective carbene dimers are obtained in quantitative yield which undergo a degradation and rearrangement sequence upon thermal exposure. Some of the species involved in these thermal reactions could be isolated and characterized, others were observed by mass spectrometric experiments. Ab initio and density functional theory (DFT) calculations provide a mechanistic rationale for the experimental observations. Since dimerization is strongly favored, classic carbene trapping reactions remain a goal to achieve.     

A Series of Low-Coordinate Iron Selenido Complexes: Reactivity of a Linear Iron(I) Silylamide towards Selenium

A variety of different low-coordinate iron selenide complexes is reported. These are obtained by reaction of the linear iron(I) silylamide K{18c6}[Fe(N(Dipp)SiMe₃)₂] (Dipp=2,6-diisopropylphenyl) with red selenium. Careful adjustment of the reaction conditions results in the formation of unique low-coordinate selenido iron complexes, namely a monoselenide bridged [2Fe−1Se]²⁺ complex, as well as mononuclear iron per- and triselenides. Further, C−H bond activation of one of the silylamide ligands by a putative terminal iron monoselenide is observed.     

Bromine Adsorption and Thermal Stability on Rh(111): A Combined XPS,LEED and DFT Study

This study addresses a fundamental question in surface science: the adsorption of halogens on metal surfaces. Using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (XPS), temperature-programmed XPS, low-energy electron diffraction (LEED) and density functional theory (DFT) calculations, we investigated the adsorption and thermal stability of bromine on Rh(111) in detail. The adsorption of elemental bromine on Rh(111) at 170 K was followed in situ by XPS in the Br 3d region, revealing two individual, coverage-dependent species, which we assign to fcc hollow- and bridge-bound atomic bromine. In addition, we find a significant shift in binding energy upon increasing coverage due to adsorbate-adsorbate interactions. Subsequent heating shows a high thermal stability of bromine on Rh(111) up to above 1000 K, indicating strong covalent bonding. To complement the XPS data, LEED was used to study the long-range order of bromine on Rh(111): we observe a (√3×√3)R30° structure for low coverages (≤0.33 ML) and a star-shaped compression structure for higher coverages (0.33–0.43 ML). Combining LEED and DFT calculations, we were able to visualize bromine adsorption on Rh(111) in real space for varying coverages.