Uranium-mediated oxidative addition and reductive elimination

This Perspective article summarises the emerging research topic of uranium-mediated oxidative addition and reductive elimination.</p

Photolytic and Reductive Activations of 2‐Arsaethynolate in a Uranium‐Triamidoamine Complex: Decarbonylative Arsenic Group‐Transfer Reactions and Trapping of a Highly Bent and Reduced Form

Little is known about the chemistry of the 2-arsaethynolate anion, but to date it has exclusively undergone fragmentation reactions when reduced. Herein, we report the synthesis of [U(Tren(TIPS))(OCAs)] (2, Tren(TIPS)=N(CH(2)CH(2)NSiiPr(3))(3)), which is the first isolable actinide-2-arsaethynolate linkage. UV-photolysis of 2 results in decarbonylation, but the putative [U(Tren(TIPS))(As)] product was not isolated and instead only [{U(Tren(TIPS))}(2)(mu-eta(2):eta(2)-As2H2)] (3) was formed. In contrast, reduction of 2 with [U(Tren(TIPS))] gave the mixed-valence arsenido [{U(Tren(TIPS))}(2)(mu-As)] (4) in very low yield. Complex 4 is unstable which precluded full characterisation, but these photolytic and reductive reactions testify to the tendency of 2-arsaethynolate to fragment with CO release and As transfer. However, addition of 2 to an electride mixture of potassium-graphite and 2,2,2-cryptand gives [{U(Tren(TIPS))}(2){mu-eta(2)(OAs):eta(2)(CAs)-OCAs}][K(2,2,2-cryptand)] (5). The coordination mode of the trapped 2-arsaethynolate in 5 is unique, and derives from a new highly reduced and bent form of this ligand with the most acute O-C-As angle in any complex to date (O-C-As angle approximate to 128 degrees). The trapping rather than fragmentation of this highly reduced O-C-As unit is unprecedented, and quantum chemical calculations reveal that reduction confers donor-acceptor character to the O-C-As unit

Evidence for ligand- and solvent-induced disproportionation of uranium(IV)

From Springer Nature via Jisc Publications RouterHistory: received 2020-05-14, accepted 2021-07-21, registration 2021-07-28, pub-electronic 2021-08-10, online 2021-08-10, collection 2021-12Publication status: PublishedFunder: RCUK | Engineering and Physical Sciences Research Council (EPSRC); doi: https://doi.org/10.13039/501100000266; Grant(s): EP/K024000/1, EP/M027015/1, EP/P001386/1, EP/S033181/1Funder: Leverhulme Trust; doi: https://doi.org/10.13039/501100000275; Grant(s): RF-2018-545\4Funder: Royal Society; doi: https://doi.org/10.13039/501100000288; Grant(s): UF110005Abstract: Disproportionation, where a chemical element converts its oxidation state to two different ones, one higher and one lower, underpins the fundamental chemistry of metal ions. The overwhelming majority of uranium disproportionations involve uranium(III) and (V), with a singular example of uranium(IV) to uranium(V/III) disproportionation known, involving a nitride to imido/triflate transformation. Here, we report a conceptually opposite disproportionation of uranium(IV)-imido complexes to uranium(V)-nitride/uranium(III)-amide mixtures. This is facilitated by benzene, but not toluene, since benzene engages in a redox reaction with the uranium(III)-amide product to give uranium(IV)-amide and reduced arene. These disproportionations occur with potassium, rubidium, and cesium counter cations, but not lithium or sodium, reflecting the stability of the corresponding alkali metal-arene by-products. This reveals an exceptional level of ligand- and solvent-control over a key thermodynamic property of uranium, and is complementary to isolobal uranium(V)-oxo disproportionations, suggesting a potentially wider prevalence possibly with broad implications for the chemistry of uranium

Exploratory Research on Overfertilization in Grain Production and Its Relationship with Financial Factors: Evidence from China

Although there have been many studies on the degree of overfertilization, there are few systematic comparative analyses on the degree of overfertilization of three major grain crops (wheat, rice, and maize) over a long time span in recent years. Whereas the studies of the influence of government efforts, individual characteristics of farmers, and economic factors on farmer’s fertilization decision ignored the financial consideration of farmers. This study aims to systematically investigate the degree of overfertilization in the production of three major grain crops in 21 provinces of China from 2004 to 2018 by developing a panel-data model, and explores the impact of financial factors on overfertilization by applying Arellano-Bover/Blundell-Bond linear dynamic panel-data estimation. The results showed an upward trend in overfertilization in the production of three grain crops from 2010 to 2018, although a decline between 2007 and 2009 may indicate that the financial crisis had a short-term impact on overfertilization. Overfertilization varied across regions, and chemical fertilizers were applied most excessively in wheat production in the Huang-Huai-Hai region and in maize in Southwest China. The analysis of financial factors showed that cash earnings from wheat and maize positively affected overfertilization, whereas cash cost and farmers’ income had opposite effects. In fact, farmers value cash earnings and cash costs rather than the time value of money. In addition, the sensitivity and cautiousness of farmers regarding economic events may indicate that farmers have a certain degree of economic rationality regarding fertilizer input in several provinces, such as Anhui and Yunnan. The study provides necessary supplements to existing research on the influence factors of overfertilization and has implications for improving the design of fertilizer sales collection methods by the government and the financial service sector

Yttrium Anilido Hydride: Synthesis, Structure, and Reactivity

The synthesis, structure, and reactivity of the yttrium anilido hydride [LY(NH(DIPP))(μ-H)]₂ (<b>3</b>; L = [MeC(N(DIPP))CHC(Me)(NCH₂CH₂NMe₂)]⁻, DIPP = 2,6-^<i>i</i>Pr₂C₆H₃)) are reported. The protonolysis reaction of the yttrium dialkyl [LY(CH₂SiMe₃)₂] (<b>1</b>) with 1 equiv of 2,6-diisopropylaniline gave the yttrium anilido alkyl [LY(NH(DIPP))(CH₂SiMe₃)] (<b>2</b>), and a subsequent σ-bond metathesis reaction of <b>2</b> with 1 equiv of PhSiH₃ offered the yttrium anilido hydride <b>3</b>. The structure of <b>3</b> was characterized by X-ray crystallography, which showed that the complex is a μ-H dimer. <b>3</b> shows high reactivity toward a variety of unsaturated substrates, including imine, azobenzene, carbodiimide, isocyanide, ketone, and Mo(CO)₆, giving some structurally intriguing products