Single metal four-electron reduction by U(ii) and masked “U(ii)” compounds

The redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)]₂[{((Me₃Si)₂N)₃U}₂(μ-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(η²-C₂Ph₂){N(SiMe₃)₂}₃], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)₂{N(SiMe₃)₂}₃], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe₃)₂}₃], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N₂Ph₂){N(SiMe₃)₂}₃], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a “clear-cut” single metal four-electron transfer in f-element chemistry.

Both a masked and the actual complex [U(ii){N(SiMe₃)₂}₃]⁺ effect the reduction of azobenzene to yield a U(vi) bis-imido species providing the first example of a “clear-cut” metal centred four-electron reduction in f-element chemistry.     

A Route to Stabilize Uranium(II) and Uranium(I) Synthons in Multimetallic Complexes

Herein, we report the redox reactivity of a multimetallic uranium complex supported by triphenylsiloxide (−OSiPh₃) ligands, where we show that low valent synthons can be stabilized via an unprecedented mechanism involving intramolecular ligand migration. The two- and three-electron reduction of the oxo-bridged diuranium(IV) complex [{(Ph₃SiO)₃(DME)U}₂(μ-O)], 4 , yields the formal “U^II/U^IV”, 5 , and “U^I/U^IV”, 6 , complexes via ligand migration and formation of uranium-arene δ-bond interactions. Remarkably, complex 5 effects the two-electron reductive coupling of pyridine affording complex 7 , which demonstrates that the electron-transfer is accompanied by ligand migration, restoring the original ligand arrangement found in 4 . This work provides a new method for controlling the redox reactivity in molecular complexes of unstable, low-valent metal centers, and can lead to the further development of f-elements redox reactivity.     

HR-MAS NMR Applications in Plant Metabolomics

Metabolomics is used to reduce the complexity of plants and to understand the underlying pathways of the plant phenotype. The metabolic profile of plants can be obtained by mass spectrometry or liquid-state NMR. The extraction of metabolites from the sample is necessary for both techniques to obtain the metabolic profile. This extraction step can be eliminated by making use of high-resolution magic angle spinning (HR-MAS) NMR. In this review, an HR-MAS NMR-based workflow is described in more detail, including used pulse sequences in metabolomics. The pre-processing steps of one-dimensional HR-MAS NMR spectra are presented, including spectral alignment, baseline correction, bucketing, normalisation and scaling procedures. We also highlight some of the models which can be used to perform multivariate analysis on the HR-MAS NMR spectra. Finally, applications of HR-MAS NMR in plant metabolomics are described and show that HR-MAS NMR is a powerful tool for plant metabolomics studies.     

Silicon‐Free SuFEx Reactions of Sulfonimidoyl Fluorides: Scope,Enantioselectivity, and Mechanism

SuFEx reactions, in which an S?F moiety reacts with a silyl‐protected phenol, have been developed as powerful click reactions. In the current paper we open up the potential of SuFEx reactions as enantioselective reactions, analyze the role of Si and outline the mechanism of this reaction. As a result, fast, high‐yielding, “Si‐free” and enantiospecific SuFEx reactions of sulfonimidoyl fluorides have been developed, and their mechanism shown, by both experimental and theoretical methods, to yield chiral products.     

Shifting Towards αVβ6 Integrin Ligands Using Novel Aminoproline-Based Cyclic Peptidomimetics

In recognition of the key role played by integrins in several life-threatening dysfunctions, the search for novel small-molecule probes that selectively recognize these surface receptors is still open and widely pursued. Inspired by previously established aminoproline (Amp)-RGD based cyclopeptidomimetics with attracting α_Vβ₃ integrin affinity and selectivity, the design and straightforward synthesis of 18 new AmpRGD chemotypes bearing additional structural variants were herein implemented, to shift toward peptide-like α_Vβ₆ integrin targeted binders. The ligand competence of the synthesized products toward α_Vβ₆ was evaluated in competitive binding assays on isolated receptors, and α_Vβ₆/α_Vβ₃ selectivity was determined for a subgroup of compounds, resulting in the identification of four very promising candidates. SAR considerations and docking simulations allowed us to appreciate the key structural features responsible for the observed activity.     

Silicon-Free SuFEx Reactions of Sulfonimidoyl Fluorides: Scope,Enantioselectivity, and Mechanism

SuFEx reactions, in which an S−F moiety reacts with a silyl-protected phenol, have been developed as powerful click reactions. In the current paper we open up the potential of SuFEx reactions as enantioselective reactions, analyze the role of Si and outline the mechanism of this reaction. As a result, fast, high-yielding, “Si-free” and enantiospecific SuFEx reactions of sulfonimidoyl fluorides have been developed, and their mechanism shown, by both experimental and theoretical methods, to yield chiral products.     

Metal–Metal Interactions in Heterobimetallic Complexes with Dinucleating Redox‐Active Ligands

The tuning of metal–metal interactions in multinuclear assemblies is a challenge. Selective P coordination of a redox‐active PNO ligand to Au^I followed by homoleptic metalation of the NO pocket with Ni^II affords a unique trinuclear Au–Ni–Au complex. This species features two antiferromagnetically coupled ligand‐centered radicals and a double intramolecular d⁸–d¹⁰ interaction, as supported by spectroscopic, single‐crystal X‐ray diffraction, and computational data. A corresponding cationic dinuclear Au–Ni analogue with a stronger d⁸–d¹⁰ interaction is also reported. Although both heterobimetallic structures display rich electrochemistry, only the trinuclear Au–Ni–Au complex facilitates electrocatalytic C?X bond activation of alkyl halides in its doubly reduced state. Hence, the presence of a redox‐active ligand framework, an available coordination site at gold, and the nature of the nickel–gold interaction appear to be essential for this reactivity.