Kyle Pearce

A new generation: Reduction of the uranium(III) metallocene [(η⁵‐C₅ ⁱ Pr₅)₂UI] with potassium graphite produces the “second‐generation” uranocene [(η⁵‐C₅ ⁱ Pr₅)₂U], which contains uranium in the formal divalent oxidation state. The geometry of [(η⁵‐C₅ ⁱ Pr₅)₂U] is that of a perfectly linear bis(cyclopentadienyl) sandwich complex.

Abstract

Reduction of the uranium(III) metallocene [(η⁵‐C₅ ⁱ Pr₅)₂UI] (1) with potassium graphite produces the “second‐generation” uranocene [(η⁵‐C₅ ⁱ Pr₅)₂U] (2), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground‐state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f³ 6d¹. Appreciable covalent contributions to the metal‐ligand bonds were determined from a computational study of 2, including participation from the uranium 5f and 6d orbitals. Whereas three unpaired electrons in 2 occupy orbitals with essentially pure 5f character, the fourth electron resides in an orbital defined by strong 7s‐6d mixing.

The painting Explosion in the alchemist's laboratory by Justus van Bentum (1670–1727) might depict a detonation of fulminating gold, giving off ruby‐red fumes. The Essay describes the history of preparation and uses of fulminating gold and silver from the late 1500s onward.

Abstract

This Essay deals with the fascinating and highly explosive compounds fulminating gold and fulminating silver, which are easily made by treatment of gold dissolved in aqua regia with ammonia, and by reaction of silver oxide or silver salts with ammonia, respectively. Fulminating gold in particular captivated the alchemists in the 16th to 18th centuries. Numerous preparations were described, as well as numerous attempts to make volatile, sublimable or distillable gold, and to use the products so obtained (which were most likely gold chlorides) to make the sought‐after tincture, which would “heal” the “impure” metals and transform them into gold, and equally be a panacea to cure all human illnesses.

Cause it's a bittersweet chemistry: The recent developments in the field of beryllium coordination chemistry are discussed. The emphasis is placed on the relation between the structure of the compounds and the corresponding reactivity.

Abstract

Given the alleged extreme toxicity of beryllium and its compounds, it is the least investigated nonradioactive element. However, beryllium exhibits unique properties among the elements and therefore the related coordination chemistry is unprecedented. With the emergence of s‐block catalysis and the introduction of low‐valent magnesium complexes as versatile reducing agents, the interest in related beryllium compounds also has increased. Therefore, some quite remarkable progress on the coordination and organometallic chemistry of beryllium has been made in the last two decades. This Minireview article gives an oversight over the relatively recent developments in this field of beryllium research. An emphasis is placed on the correlation between the structure and reactivity of the described compounds.

The first diphosphaarsenium cation has been synthesised. This cation exhibits remarkable stability because of the delocalisation of a lone pair from a planar phosphorus centre into the vacant arsenic p‐orbital.

Abstract

Stable acyclic arsenium cations R₂As⁺, isoelectronic analogues of germylenes, are rare in comparison to the corresponding phosphenium cations. The first example of a diphosphaarsenium salt, [{(Dipp)₂P}₂As][Al{OC(CF₃)₃}₄]⋅1  PhMe, is described. This salt exhibits remarkable stability due to the delocalisation of a lone pair from a planar phosphorus centre into the vacant p‐orbital at arsenic; the bonding in 2 has been probed by DFT calculations. An attempt to synthesise an analogous diphosphaphosphenium salt unexpectedly generated the cyclic phosphonium salt [cyclo‐{(Mes)P}₂P(Mes)₂][BAr^F ₄]⋅CyMe through the cyclisation of a putative phosphine‐substituted diphosphene cation intermediate.

Bandgap control: A family of PAH‐fused heterocyclic phosphonium dyes, prepared through intramolecular phosphacyclization, demonstrates remarkably rich opportunity to control the optical bandgap.

Abstract

Rationally designed cationic phospha‐polyaromatic fluorophores were prepared through intramolecular cyclization of the tertiary ortho‐(acene)phenylene‐phosphines mediated by Cu^II triflate. As a result of phosphorus quaternization, heterocyclic phosphonium salts 1 c–3 c, derived from naphthalene, phenanthrene, and anthracene cores, exhibited very intense blue to green fluorescence (Φ _em=0.38–0.99) and high photostability in aqueous medium. The structure–emission relationship was further investigated by tailoring the electron‐donating functions to the anthracene moiety to give dyes 4 c–6 c with charge‐transfer character. The latter significantly decreases the emission energy to reach near‐IR region. Thus, the intramolecular phosphacyclization renders an ultra‐wide tuning of fluorescence from 420 nm (1 c) to 780 nm (6 c) in solution, extended to 825 nm for 6 c in the solid state with quantum efficiency of approximately 0.07. The physical behavior of these new dyes was studied spectroscopically, crystallographically, and electrochemically, whereas computational analysis was used to correlate the experimental data with molecular electronic structures. The excellent stability, water solubility, and attractive photophysical characteristics make these phosphonium heterocycles powerful tools in cell imaging.

Guest Editors Dietrich Gudat, Andreas Orthaber, Chris Slootweg, and Rainer Streubel report the increasing importance of phosphorus chemistry in Europe and beyond, summarizing the contributions in this special issue in honor of the 70th and 80th birthdays of Professors Koop Lammertsma and Edgar Niecke.

A new frustration: A six‐membered cyclic frustrated phosphane/borane Lewis pair forms a macrocyclic cyclooctameric structure in the crystal and in solution at low temperature. The supramolecular frustrated Lewis pair assembly has an inner diameter of about 12 to 13 Å.

Abstract

A new six‐membered cyclic frustrated phosphane/borane Lewis pair was liberated from its HB(C₆F₅)₂ adduct by treatment with vinylcyclohexane. The system is an active frustrated Lewis pair that undergoes cycloaddition reactions with suitable π reagents and it splits dihydrogen. At room temperature in solution the new compound is a monomer, however, in the crystal and in solution at low temperature it aggregates to a thermodynamically favoured supramolecular macrocyclic cyclooctamer.

Inorganic versus organic: the molecular structures and Lewis basicities of triphenylphosphine and tris(2‐borazinyl)phosphine appear similar but their hydrolysis and oxygenation chemistry could hardly be more contrasting.

Abstract

A completely inorganic version of one of the most famous organophosphorus compounds, triphenylphosphine, has been prepared. A comparison of the crystal structures of inorganic triphenylphosphine, PBaz₃ (where Baz=B₃H₂N₃H₃) and PPh₃ shows that they have superficial similarities and furthermore, the Lewis basicities of the two compounds are remarkably similar. However, their oxygenation and hydrolysis reactions are starkly different. PBaz₃ reacts quantitatively with water to give PH₃ and with the oxidizing agent ONMe₃ to give the triply‐O‐inserted product P(OBaz)₃, an inorganic version of triphenyl phosphite; a corresponding transformation with PPh₃ is inconceivable. Thermodynamically, what drives these striking differences in the chemistry of PBaz₃ and PPh₃ is the great strength of the B−O bond.

The realities of radium

The realities of radium, Published online: 20 July 2018; doi:10.1038/s41557-018-0114-8