Isolation of Elusive HAsAsH in a Crystalline Diuranium(IV) Complex

The HAsAsH molecule has hitherto only been proposed tentatively as a short‐lived species generated in electrochemical or microwave‐plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(Tren^TIPS)}₂(μ‐η²:η²‐As₂H₂)] ( 3 , Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃; Prⁱ=CH(CH₃)₂). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back‐bonding‐type interactions from uranium to the HAsAsH π*‐orbital. This experimentally confirms the theoretically predicted excellent π‐acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane‐1,2‐diide form.     

Rapid and Efficient Copper‐Catalyzed Finkelstein Reaction of (Hetero)Aromatics under Continuous‐Flow Conditions

A general, rapid, and efficient method for the copper‐catalyzed Finkelstein reaction of (hetero)aromatics has been developed using continuous flow to generate a variety of aryl iodides. The described method can tolerate a broad spectrum of functional groups, including N‐H and O‐H groups. Additionally, in lieu of isolation, the aryl iodide solutions were used in two distinct multistep continuous‐flow processes (amidation and Mg–I exchange/nucleophilic addition) to demonstrate the flexibility of this method.     

The Phosphinoboration Reaction

The synthesis of phosphinoboronate esters containing a single P? B bond is reported, together with preliminary reactivity studies towards a range of organic substrates. These compounds add readily to aldehydes, ketones, aldimines, and α,β‐unsaturated enones to give primarily the corresponding 1,2‐addition products containing a new P? C bond. The first examples of transition‐metal‐catalyzed phosphinoborations of C‐C multiple bonds in which P? C and B? C bonds are formed in a single step are also disclosed; allenes react by a highly regioselective 1,2‐addition whereas terminal alkynes undergo a formal 1,1‐addition.     

Characterizing Pressure‐Induced Uranium CH Agostic Bonds

The diuranium(III) compound [UN′′₂]₂(μ‐η⁶:η⁶‐C₆H₆) (N′′=N(SiMe₃)₂) has been studied using variable, high‐pressure single‐crystal X‐ray crystallography, and density functional theory . In this compound, the low‐coordinate metal cations are coupled through π‐ and δ‐symmetric arene overlap and show close metal? CH contacts with the flexible methyl CH groups of the sterically encumbered amido ligands. The metal–metal separation decreases with increasing pressure, but the most significant structural changes are to the close contacts between ligand CH bonds and the U centers. Although the interatomic distances are suggestive of agostic‐type interactions between the U and ligand peripheral CH groups, QTAIM (quantum theory of atoms‐in‐molecules) computational analysis suggests that there is no such interaction at ambient pressure. However, QTAIM and NBO analyses indicate that the interaction becomes agostic at 3.2 GPa.     

Locating Gases in Porous Materials: Cryogenic Loading of Fuel‐Related Gases Into a Sc‐based Metal–Organic Framework under Extreme Pressures

An alternative approach to loading metal organic frameworks with gas molecules at high (kbar) pressures is reported. The technique, which uses liquefied gases as pressure transmitting media within a diamond anvil cell along with a single‐crystal of a porous metal–organic framework, is demonstrated to have considerable advantages over other gas‐loading methods when investigating host–guest interactions. Specifically, loading the metal–organic framework Sc₂BDC₃ with liquefied CO₂ at 2 kbar reveals the presence of three adsorption sites, one previously unreported, and resolves previous inconsistencies between structural data and adsorption isotherms. A further study with supercritical CH₄ at 3–25 kbar demonstrates hyperfilling of the Sc₂BDC₃ and two high‐pressure displacive and reversible phase transitions are induced as the filled MOF adapts to reduce the volume of the system.     

High P–T Raman study of transitions in relaxor multiferroic Pb(Fe0.5Nb0.5)O3

The vibrational and structural properties of Pb(Fe_0.5Nb_0.5)O₃ have been investigated using Raman spectroscopy up to 40 GPa at 300 K and from 300 to 415 K at selected pressures. The measurements reveal three phase transitions, at 5.5, 8.7, and 24 GPa at room temperature. The temperature dependences of the spectra indicate transitions at 1.5 GPa, at 335 and 365 K. The results are consistent with the appearance of an intermediate tetragonal P4mm phase between the ferroelectric R3m and paraelectric Pm‐3m phases. A P–T phase diagram is proposed that allows further insight into the magnetoelectric coupling present in this material. Copyright © 2015 John Wiley & Sons, Ltd.     

Nuclear resonance vibrational spectroscopy reveals the FeS cluster composition and active site vibrational properties of an O2-tolerant NAD+-reducing [NiFe] hydrogenase

Hydrogenases are complex metalloenzymes that catalyze the reversible splitting of molecular hydrogen into protons and electrons essentially without overpotential. The NAD⁺-reducing soluble hydrogenase (SH) from Ralstonia eutropha is capable of H₂ conversion even in the presence of usually toxic dioxygen. The molecular details of the underlying reactions are largely unknown, mainly because of limited knowledge of the structure and function of the various metal cofactors present in the enzyme. Here, all iron-containing cofactors of the SH were investigated by ⁵⁷Fe specific nuclear resonance vibrational spectroscopy (NRVS). Our data provide experimental evidence for one [2Fe2S] center and four [4Fe4S] clusters, which is consistent with the amino acid sequence composition. Only the [2Fe2S] cluster and one of the four [4Fe4S] clusters were reduced upon incubation of the SH with NADH. This finding explains the discrepancy between the large number of FeS clusters and the small amount of FeS cluster-related signals as detected by electron paramagnetic resonance spectroscopic analysis of several NAD⁺-reducing hydrogenases. For the first time, Fe–CO and Fe–CN modes derived from the [NiFe] active site could be distinguished by NRVS through selective ¹³C labeling of the CO ligand. This strategy also revealed the molecular coordinates that dominate the individual Fe–CO modes. The present approach explores the complex vibrational signature of the Fe–S clusters and the hydrogenase active site, thereby showing that NRVS represents a powerful tool for the elucidation of complex biocatalysts containing multiple cofactors.