Formation Of Gold-Astatine Bonds in N-Heterocyclic Carbene Complexes.

With the purpose of exploring alternatives to the poorly stable astatoaryl bond found in most At-labeled radiopharmaceuticals, the coordination between astatine and metal-NHC (NHC = N-heterocyclic carbene) complexes was investigated. To orient this work, relativistic DFT calculations were performed, highlighting a superiority of gold(I) over rhodium(I) and iridium(I), both regarding the strength of the metal-astatine bond and the metal's preference for astatine over other halogens. The DFT calculations also revealed a more stable metal-astatine bond with electron-withdrawing NHCs.

Gold-Mediated Cyclization of -Acrylamides via Energy Transfer Photocatalysis.

We disclose a gold-mediated photocyclization method for the efficient synthesis of acrylamide-derived β-lactams and 3,4-dihydroquinolin-2-ones, two privileged bioactive scaffolds. The protocol proceeds with ease, providing good yields of product while exhibiting excellent functional group tolerance at low catalyst loadings in sustainable solvents. Additionally, reaction times are significantly reduced compared with prior-art methods.

A supply-limited torrent that does not feel the heat of climate change.

Debris-flow activity in the Alps is anticipated to undergo pronounced changes in response to a warming climate. Yet, a fundamental challenge in comprehensively assessing changes in process activity is the systematic lack of long-term observational debris-flow records. Here, we reconstruct the longest, continuous time series (1626-2020) of debris flows at Multetta, a supply-limited torrential system in the Eastern Swiss Alps.

Gold(I)-N-Heterocyclic Carbene Synthons in Organometallic Synthesis.

The prominent role of gold-N-heterocyclic carbene (NHC) complexes in numerous research areas such as homogeneous (photo)catalysis, medicinal chemistry and materials science has prompted organometallic chemists to design gold-based synthons that permit access to target complexes through simple synthetic steps under mild conditions. In this review, the main gold-NHC synthons employed in organometallic synthesis are discussed. Mechanistic aspects involved in their synthesis and reactivity as well as applications of gold-NHC synthons as efficient pre-catalysts, antitumor agents and/or photo-emissive materials are presented.

Lunar eclipses illuminate timing and climate impact of medieval volcanism.

Explosive volcanism is a key contributor to climate variability on interannual to centennial timescales. Understanding the far-field societal impacts of eruption-forced climatic changes requires firm event chronologies and reliable estimates of both the burden and altitude (that is, tropospheric versus stratospheric) of volcanic sulfate aerosol. However, despite progress in ice-core dating, uncertainties remain in these key factors.

250 years of flood frequency and discharge in an ungauged Corsican mountain catchment: A dendrogeomorphic reconstruction.

The primary goal of paleoflood hydrology is to estimate the frequency and magnitude of past floods. Botanical evidence, and particularly scars on trees, has been used repeatedly as paleostage indicators to reconstruct peak discharges and flood height. Yet, these reconstructions depend on the presence of visible scars on tree stems which tend to be masked as trees grow older.

Access to Azetidines via Gold Mediated Energy Transfer Photocatalysis.

The area of energy transfer photocatalysis to generate four-membered rings is experiencing an unprecedented level of activity. Here, we report an operationally simple method toward azetidines from 2-isoxasoline-3-carboxylates and alkenes, using [Au(cbz)(NHC)] complexes as photocatalysts. The procedure enables the reaction for a wide range of substrates.

Current Siberian heating is unprecedented during the past seven millennia.

The Arctic is warming faster than any other region on Earth. Putting this rapid warming into perspective is challenging because instrumental records are often short or incomplete in polar regions and precisely-dated temperature proxies with high temporal resolution are largely lacking. Here, we provide this long-term perspective by reconstructing past summer temperature variability at Yamal Peninsula - a hotspot of recent warming - over the past 7638 years using annually resolved tree-ring records.

Energy transfer (EnT) photocatalysis enabled by gold-N-heterocyclic carbene (NHC) complexes.

We present the use of gold sensitizers [Au(SIPr)(Cbz)] (PhotAu 1) and [Au(IPr)(Cbz)] (PhotAu 2) as attractive alternatives to state-of-the-art iridium-based systems. These novel photocatalysts are deployed in [2 + 2] cycloadditions of diallyl ethers and -tosylamides. The reactions proceed in short reaction times and in environmentally friendly solvents.

Simple synthesis of [Ru(CO)(NHC)(-cymene)] complexes and their use in transfer hydrogenation catalysis.

A novel, efficient and facile protocol for the synthesis of a series of [Ru(NHC)(CO)(-cymene)] complexes is reported. This family of Ru-NHC complexes was obtained from imidazol(in)ium tetrafluoroborate or imidazolium hydrogen carbonate salts in moderate to excellent yields, employing sustainable weak base. The ruthenium complexes were successfully utilized in the transfer hydrogenation of ketones as highly active multifunctional catalysts.

A simple synthesis of [RuCl(NHC)(p-cymene)] complexes and their use in olefin oxidation catalysis.

A simple and efficient synthetic route to [RuCl(NHC)(p-cymene)] and [Ru(CO)(NHC)(p-cymene)] complexes making use of a weak base, under aerobic conditions, is reported. This method enables access to a series of NHC-ruthenium compounds with moderate to good yields under mild conditions. The Ru pre-catalysts were successfully used in olefin oxidation catalysis at low catalyst loading and reach complete conversion in short times.

A general protocol for the synthesis of Pt-NHC (NHC = N-heterocyclic carbene) hydrosilylation catalysts.

A general, user-friendly synthetic route to [Pt(NHC)(L)Cl2] and [Pt(NHC)(dvtms)] (L = DMS, Py; DMS = dimethyl sulfide, dvtms = divinyltetramethylsiloxane, Py = pyridine) complexes has been developed. The procedure is applicable to a wide range of ligands and enables facile synthetic access to key Pt(0)- and Pt(ii)-NHC complexes used in hydrosilylation catalysis.

Understanding existing and designing novel synthetic routes to Pd-PEPPSI-NHC and Pd-PEPPSI-PR pre-catalysts.

The reaction mechanism leading to the formation of cross-coupling palladium pre-catalysts of the PEPPSI family was investigated. Two intermediates were isolated and proved to be both suitable synthons to the pre-catalysts, with one permitting the design of a novel and greener user-friendly synthetic route. In light of this mechanistic understanding, the traditional one-pot method was shown to be possible using stoichiometric amounts of throw-away ligand, which represents a considerable synthetic improvement over the wasteful "in pyridine" approach.

Climatic and societal impacts of a "forgotten" cluster of volcanic eruptions in 1108-1110 CE.

Recently revised ice core chronologies for Greenland have newly identified one of the largest sulfate deposition signals of the last millennium as occurring between 1108 and 1113 CE. Long considered the product of the 1104 CE Hekla (Iceland) eruption, this event can now be associated with substantial deposition seen in Antarctica under a similarly revised chronology. This newly recognized bipolar deposition episode has consequently been deemed to reveal a previously unknown major tropical eruption in 1108 CE.

Recent flood hazards in Kashmir put into context with millennium-long historical and tree-ring records.

In September 2014, the Kashmir valley (north-west India) experienced a massive flood causing significant economic losses and fatalities. This disaster underlined the high vulnerability of the local population and raised questions regarding the resilience of Kashmiris to future floods. Although the magnitude of the 2014 flood has been considered unprecedented within the context of existing measurements, we argue that the short flow series may lead to spurious misinterpretation of the probability of such extreme events.

The Eldgjá eruption: timing, long-range impacts and influence on the Christianisation of Iceland.

The Eldgjá lava flood is considered Iceland's largest volcanic eruption of the Common Era. While it is well established that it occurred after the Settlement of Iceland (circa 874 CE), the date of this great event has remained uncertain. This has hampered investigation of the eruption's impacts, if any, on climate and society.

Imprisoned in the Cretan mountains: How relict Zelkova abelicea (Ulmaceae) trees cope with Mediterranean climate.

We investigate the sensitivity of the relict, endemic Cretan tree species Zelkova abelicea (Lam.) Boiss. (Ulmaceae) to several climate variables (temperature, precipitation and drought).

Impacts of regional climatic fluctuations on radial growth of Siberian and Scots pine at Mukhrino mire (central-western Siberia).

Ring width (TRW) chronologies from Siberian (Pinus sibirica) and Scots (Pinus sylvestris) pine trees were sampled at Mukhrino - a large mire complex in central-western Siberia - to evaluate the impacts of hydroclimatic variability on tree growth over the last three centuries. For this purpose, we compared climate-growth correlation profiles from trees growing on peat soils with those growing on adjacent mineral soils. Tree growth at both peat and mineral soils was positively correlated to air temperature during the vegetation period.

Electronic cigarette: use and perceptions among French military nurses in 2013.

Aims: Paramedical personnel are exposed to tobacco smoking. Electronic cigarettes (e-cigarettes) may be considered as a lower-risk substitute for cigarettes. The aim of the study was to estimate the prevalence of e-cigarette use, the motives for use and the perceptions among French military nurses.

Source of the great A.D. 1257 mystery eruption unveiled, Samalas volcano, Rinjani Volcanic Complex, Indonesia.

Polar ice core records attest to a colossal volcanic eruption that took place ca. A.D.