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Boron functional groups are often introduced in place of aromatic carbon-hydrogen bonds to expedite small-molecule diversification through coupling of molecular fragments.sup.1-3. Current approaches based on transition-metal-catalysed activation of carbon-hydrogen bonds are effective for the borylation of many (hetero)aromatic derivatives.sup.4,5 but show narrow applicability to azines (nitrogen-containing aromatic heterocycles), which are key components of many pharmaceutical and agrochemical products.sup.6. Here we report an azine borylation strategy using stable and inexpensive amine-borane.sup.7 reagents. Photocatalysis converts these low-molecular-weight materials into highly reactive boryl radicals.sup.8 that undergo efficient addition to azine building blocks. This reactivity provides a mechanistically alternative tactic for sp.sup.2 carbon-boron bond assembly, where the elementary steps of transition-metal-mediated carbon-hydrogen bond activation and reductive elimination from azine-organometallic intermediates are replaced by a direct, Minisci.sup.9-style, radical addition. The strongly nucleophilic character of the amine-boryl radicals enables predictable and site-selective carbon-boron bond formation by targeting the azine's most activated position, including the challenging sites adjacent to the basic nitrogen atom. This approach enables access to aromatic sites that elude current strategies based on carbon-hydrogen bond activation, and has led to borylated materials that would otherwise be difficult to prepare. We have applied this process to the introduction of amine-borane functionalities to complex and industrially relevant products. The diversification of the borylated azine products by mainstream cross-coupling technologies establishes aromatic amino-boranes as a powerful class of building blocks for chemical synthesis. Selective borylation of azines--nitrogen-containing aromatic heterocycles used in the synthesis of many pharmaceuticals--is made possible by forming a radical from an aminoborane using a photocatalyst., Author(s): Ji Hye Kim [sup.1] , Timothée Constantin [sup.1] , Marco Simonetti [sup.1] , Josep Llaveria [sup.2] , Nadeem S. Sheikh [sup.3] , Daniele Leonori [sup.1] Author Affiliations: (1) Department [...]

Author(s): Valentin V. Karasiev [sup.1] , Joshua Hinz [sup.1] , S. X. Hu [sup.1] , S. B. Trickey [sup.2] Author Affiliations: (1) Laboratory for Laser Energetics, University of Rochester, Rochester, [...]

Direct C-H functionalization can quickly increase useful structural and functional molecular complexity.sup.1-3. Site selectivity can sometimes be achieved through appropriate directing groups or substitution patterns.sup.1-4--in the absence of such functionality, most aromatic C-H functionalization reactions provide more than one product isomer for most substrates.sup.1,4,5. Development of a C-H functionalization reaction that proceeds with high positional selectivity and installs a functional group that can serve as a synthetic linchpin for further functionalization would provide access to a large variety of well-defined arene derivatives. Here we report a highly selective aromatic C-H functionalization reaction that does not require a particular directing group or substitution pattern to achieve selectivity, and provides functionalized arenes that can participate in various transformations. We introduce a persistent sulfur-based radical to functionalize complex arenes with high selectivity and obtain thianthrenium salts that are ready to engage in different transformations, via both transition-metal and photoredox catalysis. This transformation differs fundamentally from all previous aromatic C-H functionalization reactions in that it provides direct access to a large number of derivatives of complex small molecules, quickly generating functional diversity with selectivity that is not achievable by other methods. A highly site-selective aromatic C-H functionalization reaction that does not require a particular directing group or arene substitution pattern provides functionalized arenes that can participate in various transformations., Author(s): Florian Berger [sup.1] , Matthew B. Plutschack [sup.1] , Julian Riegger [sup.1] , Wanwan Yu [sup.1] , Samira Speicher [sup.1] , Matthew Ho [sup.1] , Nils Frank [sup.1] , [...]

In 1906, Theodore Lyman discovered his eponymous series of transitions in the extreme-ultraviolet region of the atomic hydrogen spectrum.sup.1,2. The patterns in the hydrogen spectrum helped to establish the emerging theory of quantum mechanics, which we now know governs the world at the atomic scale. Since then, studies involving the Lyman-[alpha] line--the 1S-2P transition at a wavelength of 121.6 nanometres--have played an important part in physics and astronomy, as one of the most fundamental atomic transitions in the Universe. For example, this transition has long been used by astronomers studying the intergalactic medium and testing cosmological models via the so-called 'Lyman-[alpha] forest'.sup.3 of absorption lines at different redshifts. Here we report the observation of the Lyman-[alpha] transition in the antihydrogen atom, the antimatter counterpart of hydrogen. Using narrow-line-width, nanosecond-pulsed laser radiation, the 1S-2P transition was excited in magnetically trapped antihydrogen. The transition frequency at a field of 1.033 tesla was determined to be 2,466,051.7 [plus or minus] 0.12 gigahertz (1[sigma] uncertainty) and agrees with the prediction for hydrogen to a precision of 5 × 10.sup.-8. Comparisons of the properties of antihydrogen with those of its well-studied matter equivalent allow precision tests of fundamental symmetries between matter and antimatter. Alongside the ground-state hyperfine.sup.4,5 and 1S-2S transitions.sup.6,7 recently observed in antihydrogen, the Lyman-[alpha] transition will permit laser cooling of antihydrogen.sup.8,9, thus providing a cold and dense sample of anti-atoms for precision spectroscopy and gravity measurements.sup.10. In addition to the observation of this fundamental transition, this work represents both a decisive technological step towards laser cooling of antihydrogen, and the extension of antimatter spectroscopy to quantum states possessing orbital angular momentum.The observation of the 1S-2P Lyman-[alpha] transition in the antihydrogen atom, the antimatter counterpart of hydrogen, is reported., Author(s): M. Ahmadi [sup.1] , B. X. R. Alves [sup.2] , C. J. Baker [sup.3] , W. Bertsche [sup.4] [sup.5] , A. Capra [sup.6] , C. Carruth [sup.7] , C. [...]

Author(s): Kumiko Yamamoto [1, 2]; Jiakun Li [1]; Jeffrey A. O. Garber [1, 2]; Julian D. Rolfes [1, 2]; Gregory B. Boursalian [1, 2]; Jannik C. Borghs [2]; Christophe Genicot [...]

Author(s): Jin Liu [1]; Qingyang Hu [1, 2]; Duck Young Kim [2]; Zhongqing Wu [3]; Wenzhong Wang [3]; Yuming Xiao [4]; Paul Chow [4]; Yue Meng [4]; Vitali B. Prakapenka [...]

Author(s): Waiz Karim [1, 2, 3]; Clelia Spreafico [4]; Armin Kleibert [5]; Jens Gobrecht [2]; Joost VandeVondele [4]; Yasin Ekinci (corresponding author) [2]; Jeroen A. van Bokhoven (corresponding author) [1, [...]

Switching of static friction and adhesion of a liquid drop on a corrugated solid boron nitride surface is linked to the intercalation of hydrogen, which changes the electric field of in-plane dipole rings and thus reduces the adsorption energy. Stiction versus adhesion in a single liquid drop Stiction, or static friction, is the force required to persuade an object to start sliding across a surface. It is technologically important in devices with moving parts in contact, but is not well understood. Stijn Mertens et al. describe an inorganic model system for the study of the relationships between surface wetting, stiction, adhesion and lubrication. The system is a hexagonal boron nitride monolayer that can be electrochemically switched by intercalation of hydrogen between a corrugated and a flat morphology. The change in the surface structure of the boron nitride alters the adhesion and its balance with stiction of an aqueous drop sliding across the monolayer. The work of adhesion increases in going from the flat to the corrugated surface, whereas the stiction threshold does not change significantly. Thus the authors make a quantitative connection between the macroscopic properties of stiction and adhesion as a result of structural control at the atomic scale. When a gecko moves on a ceiling it makes use of adhesion and stiction. Stiction--static friction--is experienced on microscopic and macroscopic scales and is related to adhesion and sliding friction.sup.1. Although important for most locomotive processes, the concepts of adhesion, stiction and sliding friction are often only empirically correlated. A more detailed understanding of these concepts will, for example, help to improve the design of increasingly smaller devices such as micro- and nanoelectromechanical switches.sup.2. Here we show how stiction and adhesion are related for a liquid drop on a hexagonal boron nitride monolayer on rhodium.sup.3, by measuring dynamic contact angles in two distinct states of the solid-liquid interface: a corrugated state in the absence of hydrogen intercalation and an intercalation-induced flat state. Stiction and adhesion can be reversibly switched by applying different electrochemical potentials to the sample, causing atomic hydrogen to be intercalated or not. We ascribe the change in adhesion to a change in lateral electric field of in-plane two-nanometre dipole rings.sup.4, because it cannot be explained by the change in surface roughness known from the Wenzel model.sup.5. Although the change in adhesion can be calculated for the system we study.sup.6, it is not yet possible to determine the stiction at such a solid-liquid interface using ab initio methods. The inorganic hybrid of hexagonal boron nitride and rhodium is very stable and represents a new class of switchable surfaces with the potential for application in the study of adhesion, friction and lubrication., Author(s): Stijn F. L. Mertens [sup.1] [sup.2] , Adrian Hemmi [sup.3] , Stefan Muff [sup.3] , Oliver Gröning [sup.4] , Steven De Feyter [sup.1] , Jürg Osterwalder [sup.3] , Thomas [...]

Phthaloyl peroxide functions as a selective oxidant of C-H bonds in the transformation of arenes to phenols under mild conditions, in a reaction that is compatible with a wide array of functional groups. Phenol synthesis without the fuss The selective oxidation of the C-H bond is central to synthetic organic chemistry, both by producing the target functional molecule and in 'build-up' molecules on more complex syntheses. Here Dionicio Siegel and colleagues use computational analysis to develop a new method of transforming arenes to phenols that requires much milder conditions than most established routes. They use phthaloyl peroxide as a selective oxidant in a reaction that does not require a metal catalyst, is entropically favourable and has high tolerance for a variety of different functional groups. Methods for carbon-hydrogen (C-H) bond oxidation have a fundamental role in synthetic organic chemistry, providing functionality that is required in the final target molecule or facilitating subsequent chemical transformations. Several approaches to oxidizing aliphatic C-H bonds have been described, drastically simplifying the synthesis of complex molecules.sup.1,2,3,4,5,6. However, the selective oxidation of aromatic C-H bonds under mild conditions, especially in the context of substituted arenes with diverse functional groups, remains a challenge. The direct hydroxylation of arenes was initially achieved through the use of strong Brønsted or Lewis acids to mediate electrophilic aromatic substitution reactions with super-stoichiometric equivalents of oxidants, significantly limiting the scope of the reaction.sup.7. Because the products of these reactions are more reactive than the starting materials, over-oxidation is frequently a competitive process. Transition-metal-catalysed C-H oxidation of arenes with or without directing groups has been developed, improving on the acid-mediated process; however, precious metals are required.sup.8,9,10,11,12,13. Here we demonstrate that phthaloyl peroxide functions as a selective oxidant for the transformation of arenes to phenols under mild conditions. Although the reaction proceeds through a radical mechanism, aromatic C-H bonds are selectively oxidized in preference to activated [Formula omitted]-H bonds. Notably, a wide array of functional groups are compatible with this reaction, and this method is therefore well suited for late-stage transformations of advanced synthetic intermediates. Quantum mechanical calculations indicate that this transformation proceeds through a novel addition-abstraction mechanism, a kind of 'reverse-rebound' mechanism as distinct from the common oxygen-rebound mechanism observed for metal-oxo oxidants. These calculations also identify the origins of the experimentally observed aryl selectivity., Author(s): Changxia Yuan [sup.1] , Yong Liang [sup.2] , Taylor Hernandez [sup.1] , Adrian Berriochoa [sup.1] , Kendall N. Houk [sup.2] , Dionicio Siegel [sup.1] Author Affiliations: (1) Department of [...]

Author(s): Chip Le [1]; Yufan Liang [1]; Ryan W. Evans [1]; Ximing Li [1]; David W. C. MacMillan (corresponding author) [1] The functionalization of carbonhydrogen (CH) bonds is one of [...]

Author(s): Yuta Fujiwara [1, 3]; Janice A. Dixon [1, 3]; Fionn O'Hara [1, 3]; Erik Daa Funder [1]; Darryl D. Dixon [1]; Rodrigo A. Rodriguez [1]; Ryan D. Baxter [1]; [...]

Enzyme structure reveals key ingredients for making hydrogen. [...]