Prior to the year 2000, non‐aqueous uranium chemistry mainly involved metallocene and classical alkyl, amide, or alkoxide compounds as well as established carbene, imido, and oxo derivatives. Since ...then, there has been a resurgence of the area, and dramatic developments of supporting ligands and multiply bonded ligand types, small‐molecule activation, and magnetism have been reported. This Review 1) introduces the reader to some of the specialist theories of the area, 2) covers all‐important starting materials, 3) surveys contemporary ligand classes installed at uranium, including alkyl, aryl, arene, carbene, amide, imide, nitride, alkoxide, aryloxide, and oxo compounds, 4) describes advances in the area of single‐molecule magnetism, and 5) summarizes the coordination and activation of small molecules, including carbon monoxide, carbon dioxide, nitric oxide, dinitrogen, white phosphorus, and alkanes.
Rise like a phoenix? In the last several years, there has been a resurgence of non‐aqueous uranium chemistry, in particular dealing with the development of new ligand classes and complexes with multiple bonding, single‐molecule magnetism, and the activation of small molecules, such as N2, CO2, and alkanes. Owing to its unusual coordination properties, uranium is remarkably different from transition metals, but also from other actinides.
Ever since the discovery that certain manganese clusters retain their magnetisation for months at low temperatures, there has been intense interest in molecular nanomagnets because of potential ...applications in data storage, spintronics, quantum computing, and magnetocaloric cooling. In this Tutorial Review, we summarise some key historical developments, and centre our discussion principally on the increasing trend to exploit the large magnetic moments and anisotropies of f-element ions. We focus on the important theme of strategies to improve these systems with the ultimate aim of developing materials for ultra-high-density data storage devices. We present a critical discussion of key parameters to be optimised, as well as of experimental and theoretical techniques to be used to this end.
Historical developments, trends, pitfalls and strategies in improving f-element single molecule magnets are described.
There is long-standing interest in nonaqueous uranium chemistry because of fundamental questions about uranium’s variable chemical bonding and the similarities of this pseudo-Group 6 element to its ...congener d-block elements molybdenum and tungsten. To provide historical context, with reference to a conference presentation slide presented around 1988 that advanced a defining collection of top targets, and the challenge, for synthetic actinide chemistry to realize in isolable complexes under normal experimental conditions, this Viewpoint surveys progress against those targets, including (i) CO and related π-acid ligand complexes, (ii) alkylidenes, carbynes, and carbidos, (iii) imidos and terminal nitrides, (iv) homoleptic polyalkyls, -alkoxides, and -aryloxides, (v) uranium–uranium bonds, and (vi) examples of topics that can be regarded as branching out in parallel from the leading targets. Having summarized advances from the past four decades, opportunities to build on that progress, and hence possible future directions for the field, are highlighted. The wealth and diversity of uranium chemistry that is described emphasizes the importance of ligand–metal complementarity in developing exciting new chemistry that builds our knowledge and understanding of elements in a relativistic regime.
•Cyclobutadienyl complexes of uranium reviewed.•Absence of cyclopentadienyl complexes of uranium noted.•Arene complexes of uranium reviewed.•Cycloheptatrienyl complexes of uranium ...reviewed.•Cyclooctatetraenyl complexes of uranium reviewed.
The chemistry of arene complexes of uranium has for over half a century been an important facet of organoactinide chemistry. Within this extensive and burgeoning field, in the past two decades inverted sandwich complexes have emerged incorporating cyclobutadienyl, arene, cycloheptatrienyl, and cyclooctatetraenyl ligands. Herein, the field is reviewed with an emphasis on well-defined molecular species that have been unambiguously characterised by X-ray crystallography.
“Lanthanides find extensive applications in displays, magnets, batteries, contrast reagents, and biological probes, and actinides are central to nuclear fuel and fire alarms. … Given the very basics ...of lanthanide and actinide chemistry are being frequently redefined this is a fascinating and exciting area that promises many surprises in the future. …” Read more in the Guest Editorial by S. T. Liddle.
Although reductive cleavage of dinitrogen (N2) to nitride (N3−) and hydrogenation with dihydrogen (H2) to yield ammonia (NH3) is accomplished in heterogeneous Haber–Bosch industrial processes on a ...vast scale, sequentially coupling these elementary reactions together with a single metal complex remains a major challenge for homogeneous molecular complexes. Herein, we report that the reaction of a chloro titanium triamidoamine complex with magnesium effects complete reductive cleavage of N2 to give a dinitride dititanium dimagnesium ditriamidoamine complex. Tandem H2 splitting by a phosphine–borane frustrated Lewis pair (FLP) shuttles H atoms to the N3−, evolving NH3. Isotope labelling experiments confirmed N2 and H2 fixation. Though not yet catalytic, these results give unprecedented insight into coupling N2 and H2 cleavage and N−H bond formation steps together, highlight the importance of heterobimetallic cooperativity in N2 activation, and establish FLPs in NH3 synthesis.
The reaction of a chloro titanium triamidoamine complex with magnesium effects complete reductive cleavage of N2 to give a dinitride dititanium dimagnesium ditriamidoamine complex. Tandem H2 splitting by a phosphine–borane frustrated Lewis pair (FLP) shuttles H atoms to the N3− ion, evolving NH3. Isotope labelling experiments confirmed N2 and H2 fixation.
Catalytic reduction of N2 to NH3 by a Ti complex has been achieved, thus now adding an early d‐block metal to the small group of mid‐ and late‐d‐block metals (Mo, Fe, Ru, Os, Co) that catalytically ...produce NH3 by N2 reduction and protonolysis under homogeneous, abiological conditions. Reduction of TiIV(TrenTMS)X (X=Cl, 1A; I, 1B; TrenTMS=N(CH2CH2NSiMe3)3) with KC8 affords TiIII(TrenTMS) (2). Addition of N2 affords {(TrenTMS)TiIII}2(μ‐η1:η1‐N2) (3); further reduction with KC8 gives {(TrenTMS)TiIV}2(μ‐η1:η1:η2:η2‐N2K2) (4). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords {(TrenTMS)TiIV}2(μ‐η1:η1‐N2)K(B15C5)22 (5). Complexes 3–5 treated under N2 with KC8 and R3PHI, (the weakest H+ source yet used in N2 reduction) produce up to 18 equiv of NH3 with only trace N2H4. When only acid is present, N2H4 is the dominant product, suggesting successive protonation produces {(TrenTMS)TiIV}2(μ‐η1:η1‐N2H4)I2, and that extruded N2H4 reacts further with R3PHI/KC8 to form NH3.
Catalytic reduction of N2 to NH3 by a Ti complex has been achieved, thus now adding an early d‐block metal to the small group of mid‐ and late‐d‐block metals (Mo, Fe, Ru, Os, Co) that catalytically produce NH3 by N2 reduction and protonolysis under homogeneous, abiological conditions.
Despite the burgeoning field of uranium-ligand multiple bonds, analogous complexes involving other actinides remain scarce. For thorium, under ambient conditions only a few multiple bonds to carbon, ...nitrogen, oxygen, sulfur, selenium and tellurium are reported, and no multiple bonds to phosphorus are known, reflecting a general paucity of synthetic methodologies and also problems associated with stabilising these linkages at the large thorium ion. Here we report structurally authenticated examples of a parent thorium(IV)-phosphanide (Th-PH
), a terminal thorium(IV)-phosphinidene (Th=PH), a parent dithorium(IV)-phosphinidiide (Th-P(H)-Th) and a discrete actinide-phosphido complex under ambient conditions (Th=P=Th). Although thorium is traditionally considered to have dominant 6d-orbital contributions to its bonding, contrasting to majority 5f-orbital character for uranium, computational analyses suggests that the bonding of thorium can be more nuanced, in terms of 5f- versus 6d-orbital composition and also significant involvement of the 7s-orbital and how this affects the balance of 5f- versus 6d-orbital bonding character.
Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal-ligand bonds. Conversely, in high oxidation state actinide complexes ...the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle.
PDF
