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Bimetallic CpMM'Nacnac molecules with group 2 and 12 metals (M=Be, Mg, Ca, Zn, Cd, Hg) that contain novel metal‐metal bonding have been investigated in a theoretical study of their molecular and electronic structure, thermodynamic stability, and metal‐metal bonding. In all cases the metal‐metal bonds are characterized as electron‐sharing covalent single bonds from natural bond orbital (NBO) and energy‐decomposition analysis with natural orbitals of chemical valence (EDA‐NOCV) analysis. The sum of [MM′] charges is relatively constant, with all complexes exhibiting a [MM′]2+ core. Quantum theory of atoms in molecules (QTAIM) analysis indicates the presence of non‐nuclear attractors (NNA) in the metal‐metal bonds of the BeBe, MgMg, and CaCa complexes. There is substantial electron density (0.75–1.33 e) associated with the NNAs, which indicates that these metal‐metal bonds, while classified as covalent electron‐sharing bonds, retain significant metallic character that can be associated with reducing reactivity of the complex. The predicted stability of these complexes, combined with their novel covalent metal‐metal bonding and potential as reducing agents, make them appealing targets for the synthesis of new metal‐metal bonds. [ABSTRACT FROM AUTHOR]

Airborne mineral dust is sensitive to climatic changes, but its response to orbital forcing is still not fully understood. Here, we present a reconstruction of dust input to the Subarctic Pacific Ocean covering the past 190 kyr. The dust composition record is indicative of source moisture conditions, which were dominated by precessional variations. In contrast, the dust flux record is dominated by obliquity variations and displays an out‐of‐phase relationship with a dust record from the mid‐latitude North Pacific Ocean. Climate model simulations suggest precession likely drove changes in the aridity and extent of dust source regions. Additionally, the obliquity variations in dust flux can be explained by meridional shifts in the North Pacific westerly jet, driven by changes in the meridional atmospheric temperature gradient. Overall, our findings suggest that North Pacific dust input was primarily modulated by orbital‐controlled source aridity and the strength and position of the westerly winds. Plain Language Summary: Glacial‐interglacial climate variations can affect dust transport to the ocean, but the controls on past dust fluxes to the North Pacific Ocean remain poorly constrained. This region is important because fertilization of phytoplankton growth by dust‐borne iron may have contributed to lower glacial atmospheric CO2, and dust records could also constrain the past dynamics of the North Pacific westerly winds. Here, we highlight the dominance of obliquity cycles in modulating latitudinal shifts of the westerly winds and, in turn, dust inputs. In contrast, precession regulates the aridity of the dust source regions, which determines both dust emission rates and composition. Such orbital‐scale fluctuations in the dust flux could influence ocean‐atmosphere interactions in the middle and high northern latitudes, with implications for global atmospheric circulation and ocean carbon storage. Key Points: Moisture availability in Asian dust source regions to the North Pacific Ocean were controlled by precessionNorth Pacific dust flux reveals dominant obliquity variations, but is out‐of‐phase at different latitudesThe westerlies in the Northern Hemisphere were primarily modulated by obliquity cycles in the late Pleistocene [ABSTRACT FROM AUTHOR]

Sedimentary deposits from the northern South China Sea (SCS) can provide important constraints on past changes in ocean currents and the East Asian summer monsoon (EASM) in this region. However, the interpretation of such records spanning the last deglaciation is complicated because sea‐level change may also have influenced the depositional processes and patterns. Here, we present new records of grain size, clay mineralogy, and magnetic mineralogy spanning the past 24 kyr from both shallow and deep‐water sediment cores in the northern SCS. Our multi‐proxy comparison among multiple cores helps constrain the influence of sea‐level change, providing confidence in interpreting the regional climate‐forced signals. After accounting for the influence of sea‐level change, we find that these multi‐proxy records reflect a combination of changes in (a) the strength of the North Pacific Intermediate Water inflow, (b) the EASM strength, and (c) the Kuroshio Current extent. Overall, this study provides new insights into the roles of varying terrestrial weathering and oceanographic processes in controlling the depositional record on the northern SCS margin in response to climate and sea‐level fluctuations. Plain Language Summary: Sediments in the South China Sea (SCS) provide important records of past changes in the ocean circulation and atmospheric patterns in the Pacific Ocean. However, the interpretation of sedimentary archives from this region in terms of changes in the ocean currents or the climate‐driven sediment supply can be challenging because of the potential influence of global sea‐level fluctuations. In order to better constrain these multiple controls on the sedimentary regime of the northern SCS, we present new mineralogical records from sediment cores collected from both shallow‐ and deep‐water sites. After assessing the effects of sea‐level change, we find that the clay mineral assemblage in shallow sites from the northern SCS can generally be used to reconstruct the evolution of the East Asian summer monsoon. In deep‐water sites, the clay mineralogy instead reflects changes in the relative abundance of sediment supplied from Taiwan compared to Luzon, revealing an enhanced inflow of the Kuroshio Current during the mid‐late Holocene. Furthermore, millennial‐scale variability in the North Pacific Intermediate Water inflow can be traced using changes in magnetic mineralogy and the inflow appears to have been stronger at the end of the last ice age. Key Points: Sedimentary records from shallow and deep‐water sites have differing sensitivities to changes in ocean currents and the East Asian monsoonClay mineralogy in shallow sites reflects sea‐level change, while deep‐water records respond to incursion of the Kuroshio CurrentMagnetic grain‐size indicates stronger deep currents during Heinrich Stadial 1, associated with the North Pacific Intermediate Water [ABSTRACT FROM AUTHOR]

The addition of non‐benzenoid quinones, acenapthenequinone or aceanthrenequinone, to the 9‐carbene‐9‐borafluorene monoanion (1) affords the first examples of dianionic 10‐membered bora‐crown ethers (2–5), which are characterized by multi‐nuclear NMR spectroscopy (1H, 13C, 11B), X‐ray crystallography, elemental analysis, and UV/Vis spectroscopy. These tetraoxadiborecines have distinct absorption profiles based on the positioning of the alkali metal cations. When compound 4, which has a vacant C4B2O4 cavity, is reacted with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate, a color change from purple to orange serves as a visual indicator of metal binding to the central ring, whereby the Na+ ion coordinates to four oxygen atoms. A detailed theoretical analysis of the calculated reaction energetics is provided to gain insight into the reaction mechanism for the formation of 2–5. These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate. [ABSTRACT FROM AUTHOR]

Deep atmospheric convection in the Indo‐Pacific Warm Pool (IPWP) represents a major source of heat and moisture, thereby affecting the global climate, but its past changes remain debated. Here, we present sub‐millennial clay mineralogy and elemental records spanning the last 40 Kyr from within the IPWP. From these data, we infer millennial‐scale fluctuations in precipitation, with generally lower precipitation during Heinrich Stadials 1–4, corresponding to El Niño‐like conditions. Higher precipitation coincided with the warm interstadials, accompanied by La Niña‐like conditions. Moreover, our record indicates the lowest precipitation occurred during the late Holocene, supporting the hypothesis of a stronger‐than‐modern Walker circulation during the Last Glacial Maximum. In combination with other proxy records and TraCE‐21 modeling results, we recognize a distinct spatial heterogeneity of precipitation within the IPWP, resulting from the dominant influences of the ENSO‐like system and migration of the Intertropical Convergence Zone in the eastern and western IPWP, respectively. Plain Language Summary: Tropical rainfall systems in the Indo‐Pacific Warm Pool (IPWP) play a significant role in transferring energy and moisture. However, their millennial‐scale variabilities in precipitation during the past remain poorly understood. Here, we provide sub‐millennial sediment mineralogy and elemental reconstructions spanning the last 40,000 years from a sediment core in the IPWP. We infer that variability in precipitation induced by atmospheric convection in the IPWP is the main factor controlling the variability in our data through time. Hence, we interpret our records to reflect millennial‐scale fluctuations in precipitation, with lower precipitation during cool stadial periods and higher precipitation during warm interstadials. Such variability corresponds to the changing zonal state of the tropical Pacific atmosphere‐ocean system, in a pattern similar to the modern‐day. Additionally, our record indicates that precipitation was weaker during the late Holocene than during the Last Glacial Maximum (LGM), suggesting that the Pacific atmospheric zonal circulation was stronger during the LGM than today. Furthermore, a model‐data comparison reveals distinct spatial heterogeneity in the precipitation changes, with precipitation in the eastern IPWP (West Pacific) likely controlled mostly by the tropical Pacific atmosphere‐ocean system, whereas precipitation in the western IPWP (Indian Ocean) was driven by latitudinal movement of the Intertropical Convergence Zone. Key Points: We present sub‐millennial clay mineral and elemental records from the Indo‐Pacific Warm Pool spanning the last 40 KyrOur records indicate higher precipitation during La Niña‐like conditions and lower precipitation during El Niño‐like conditionsDifferent patterns and controls on precipitation variability between the eastern and western Indo‐Pacific regions are revealed [ABSTRACT FROM AUTHOR]

The relationship between ocean circulation and monsoon systems over orbital to sub‐millennial timescales is a crucial but poorly constrained component of the climate system. Here, using foraminiferal and detrital neodymium (Nd) isotope records from the intermediate‐depth northern Indian Ocean, we provide new evidence revealing that both monsoon‐driven weathering inputs and water mass advection from the Southern Ocean influenced past seawater Nd isotope changes in this region. Our results suggest that Indian Summer Monsoon weakening coincided with enhanced northward Antarctic Intermediate Water (AAIW) advection during the last deglaciation, reflecting a strong interhemispheric coupling. In contrast, the Early Holocene was characterized by enhanced monsoon strength but persistently strong AAIW inflow, indicating a relationship in the opposite sense. These differing interhemispheric relationships indicate asynchronous changes in the global atmosphere—ocean—climate system, and may represent a previously unrecognized component of the ocean‐atmosphere reorganization during the deglacial to Holocene transition. Plain Language Summary: Deciphering the interactions between processes in the Northern and Southern hemispheres is crucial for understanding the mechanisms of paleoclimate change, and therefore for predicting future climate evolution. Resolving the nature of such interactions requires high‐resolution datasets from key components of the system. To this end, we present a new intermediate‐depth foraminiferal neodymium (Nd) isotope record from the Indian Ocean covering the last 17,000 years at an unprecedented resolution of ∼200 years. Variability in this Nd isotope record reflects both changes in regional Nd inputs related to continental weathering driven by the Indian Summer Monsoon (ISM), and changes in the Nd signal carried northwards from the Southern Ocean by Antarctic Intermediate Water (AAIW). By disentangling these continental weathering and ocean circulation signals, we can compare Northern and Southern Hemisphere climate processes on sub‐millennial timescales. We found that ISM weakening coincided with enhanced northward AAIW advection during the last deglaciation, whereas enhanced monsoonal activity was accompanied by persistently strong intermediate water inflow during the Early Holocene. This variable interhemispheric connection between the summer monsoon and intermediate water advection may have played a crucial role in the last deglacial climate transition. Key Points: We present a 17 kyr record of foraminiferal Nd isotopes from the intermediate‐depth northern Indian Ocean with a resolution of ∼200 yearsBoth regional Himalayan weathering inputs and intermediate water advection from the Southern Ocean influenced the recordDifferent interhemispheric relationships are revealed between Antarctic Intermediate Water and the Indian Summer Monsoon during the last deglaciation compared to the Early Holocene [ABSTRACT FROM AUTHOR]

A theoretical investigation of ligand‐stabilized MX diatomics (M = group 13, X = group 15 element) with N‐heterocyclic carbene (NHC) ligands has been carried out to assess bonding and electronic structure. Binding of two ligands in the form L‐MX‐L is generally preferred over binding of a single ligand as L‐MX or MX‐L. Binding of carbene donor ligands is predicted to be thermodynamically favorable for all the systems, and is very favorable for the lighter group 15 systems (nitrogen and phosphorus). Detailed analysis of the bonding in these complexes has been carried out with energy decomposition analysis (EDA). In all cases, the carbene to boron and carbene to nitrogen bonding is described as an electron‐sharing double bond with both σ and π bonding interactions. For the heavier elements, bonding to C (except for PC interactions) is best described as a donor‐acceptor σ single bond. [ABSTRACT FROM AUTHOR]

To examine the applicability of different leaching methods used to extract secondary oxides from silicate solids for lithium isotope (δ7Li) measurement, this study has conducted leaching experiments on five different types of silicate solids, including a fresh basalt, two weathered basalts, a Yellow River sediment (loess‐dominated) and a shale. Four factors were assessed in the experiments: the concentration of the leaching reagent hydroxylamine hydrochloride (HH), the leaching temperature (20 °C vs 95 °C), the leaching time and the reagent/solid ratio. Based on elemental concentrations and Li isotopes, 0.04 mol l−1 hydroxylamine hydrochloride (HH) in 25% v/v acetic acid at room temperature for 1 h with 40 ml g−1 reagent/solid ratio is recommended. At high temperatures, low δ7Li and high magnesium/iron ratios indicate that minerals other than secondary oxides are dissolved. With increased leaching time, there is no evidence for Li isotopic fractionation at room temperature. However, longer leaching time or increased reagent/solid ratios may increase the risk of leaching from non‐oxide phases. Meanwhile, results suggest that low concentrations of HH are not sufficient to target the secondary oxides evenly, while high concentrations of HH can leach out more non‐oxides. We also examined the optimal oxide leaching method within a full sequential leaching procedure (i.e., exchangeable, carbonate, oxide, clay and residual phases). Elemental concentrations show that no elements exist exclusively in oxides, so it is essential to analyse multi‐elemental concentrations to verify that the leaching has accessed this phase in a given sample. Comparing secondary oxides with their corresponding solutions, we estimate the isotopic fractionation (Δ7Lioxide‐solution) is −16.8‰ to −27.7‰. [ABSTRACT FROM AUTHOR]

Evidence on West Antarctic Ice Sheet (WAIS) instability through Pleistocene glacial/interglacial cycles can provide fundamental constraints on interactions between the climate system and cryosphere. To explore such ice sheet‐ocean‐climate processes on orbital timescales over the last ∼770 ka, we provide continuous records of iceberg‐rafted debris (IRD) content and clay mineralogy, supported by detrital Sr‐Nd isotopes from the pronounced IRD peaks, in gravity core ANT34/A2‐10 from the Amundsen abyssal plain. The IRD record reveals interglacial WAIS instability since ∼770 ka, while comparison to the clay mineralogy record and published records of regional oceanic and atmospheric forcing suggests a temporal link with a strengthened Antarctic Circumpolar Current, enhanced deepwater ventilation, and poleward‐shifted southern westerly winds. In addition, the Sr‐Nd isotope signature of the detrital sediments indicates a shift in provenance around Marine Isotope Stage (MIS) 16, potentially linked to regional oceanic circulation changes. We suggest that an expanded Ross Gyre was important for controlling iceberg trajectories and sediment transport to the site before MIS 16, whereas modern‐like iceberg trajectories were established after MIS 16, probably related to a poleward shift of the Amundsen Sea Low after the end of the Mid‐Pleistocene Transition. This reorganization of the ocean and atmospheric circulation was followed by an interval of enhanced WAIS variability during MIS 15 to 13, which was linked to strong orbital and ocean forcing. These insights into the role of ocean‐atmosphere forcing on the past behavior of the WAIS may improve our framework for understanding future changes in this region. Plain Language Summary: Understanding the vulnerability of the West Antarctic Ice Sheet (WAIS) to a warming climate is critical for constraining its future contributions to global sea‐level rise. Previous studies on marine sediment cores have provided evidence for WAIS instability in response to warming ocean waters during recent glacial/interglacial cycles. Here, we extend such work over a longer timescale by generating iceberg‐rafted debris (IRD) content and clay mineralogy records from the Amundsen Sea offshore of West Antarctica back to ∼770 ka. Enhanced IRD content during warm interglacial periods provides evidence for the instability of the WAIS and was accompanied by a shift in clay mineralogy. These changes also coincided with a strengthened Antarctic Circumpolar Current, poleward‐shifted southern westerly winds, and improved deepwater ventilation, as indicated by existing studies. This comparison supports ocean forcing as a driver of WAIS instability since ∼770 ka. We also measured strontium and neodymium isotope signatures on selected samples, revealing a switch in sediment supply around Marine Isotope Stage 16 that was probably related to the reorganization of atmospheric and oceanic circulation. The subsequent interval of strong orbital and ocean forcing led to pronounced WAIS variability from ∼480 to 580 ka. These findings improve our framework for understanding future changes in this region. Key Points: Interglacial ocean‐forced instability of the West Antarctic Ice Sheet (WAIS) has existed since at least ∼770 kaDifferences in sediment provenance before and after Marine Isotope Stage (MIS) 16 may relate to different states of high‐latitude atmospheric and ocean circulationStrong ocean and orbital forcing may have enhanced WAIS instability from MIS 13 to MIS 15 [ABSTRACT FROM AUTHOR]

Borepin, a 7‐membered boron‐containing heterocycle, has become an emerging molecular platform for the development of new materials and optoelectronics. While electron‐deficient borepins are well‐established, reduced electron‐rich species have remained elusive. Herein we report the first isolable, crystalline borepin radical (2 a, 2 b) and anion (3 a, 3 b) complexes, which have been synthesized by potassium graphite (KC8) reduction of cyclic(alkyl)(amino) carbene‐dibenzo[b,d]borepin precursors. Borepin radicals and anions have been characterized by EPR or NMR, elemental analysis, X‐ray crystallography, and cyclic voltammetry. In addition, the bonding features have been investigated computationally using density functional theory. [ABSTRACT FROM AUTHOR]

Tropical marginal seas host important sedimentary archives that may be exploited to reveal past changes in continental erosion, chemical weathering, and ocean dynamics. However, these records can be challenging to interpret due to the complex interactions between climate and particulate transport across ocean margins. For the southern South China Sea over the last 90 Kyr, we observe a contrasting temporal relationship between the deposition of clay minerals and magnetic minerals, which were associated with two different hydrodynamic modes. Fine‐grained clay minerals can be carried in suspension by ocean currents, leading to a rapid response to regional climate‐driven inputs. In contrast, changes in magnetic mineralogy were linked to glacial‐interglacial sea level variability, from which we infer a control by bedload transport and resuspension. Overall, this study indicates that the transfer pathways and mechanisms imparted by varying hydrodynamic conditions exert a substantial influence on the distribution of terrigenous material in continental margin sediments. Plain Language Summary: Sediments that accumulate in the ocean along continental margins contain the minerals that were eroded and transported by rivers on the nearby land masses. Past changes in the composition of such sediments can be used to reconstruct the history of physical erosion and chemical weathering on the continents, but can also be affected by ocean dynamics over orbital and millennial timescales. Here, clay mineralogy, sediment grain size, and rock magnetic signatures are measured in a core from the continental slope of the southern South China Sea, spanning the last 90 thousand years. Differences between the clay mineral and magnetic records, which are linked to finer and coarser sediment fractions respectively, indicate that specific mechanisms and timescales influenced sediment transport to the core site. This depositional framework must be considered when interpreting the timing of changes in weathering and erosion proxies hosted in sediment records from marginal seas. Specifically, fine‐grained clay minerals may reveal a rapid response to continental weathering changes, whereas the magnetic records are influenced by the transport of denser coarser‐grained minerals under the influence of sea level change. In addition, this framework could potentially serve as an indicator of past sea level change on wide continental shelves. Key Points: In the southern South China Sea, clay mineralogy responds rapidly to climate‐driven changes in inputs on orbital timescalesMagnetic content within the coarser and denser fraction is influenced by sea level change, through bedload and resuspension transportThis depositional framework may serve as a guideline for evaluating sea level change on wide continental shelves over orbital timescales [ABSTRACT FROM AUTHOR]

Processes controlling environmental change in the subarctic Pacific Ocean on millennial to orbital timescales are not well understood. Here we use a 230‐kyr sedimentary record from the northwest Pacific Ocean to assess the response of late Pleistocene sediment dynamics to orbital forcing. Combining a source‐to‐sink perspective based on sedimentological records with climate model reanalysis, we reveal that fluctuations in sediment provenance were closely linked to obliquity‐forced changes in atmospheric circulation modes. Specifically, the position of the Aleutian Low controlled sediment transport from the Bering Sea and Aleutian Arc sources. Furthermore, a distinct shift in North Pacific ocean circulation during the Last Glacial Maximum may have been related to a strengthened Siberian High. The coincidence of atmospheric mode switches with changes in sea‐ice extent and North Pacific Intermediate Water formation in the marginal seas suggests that this coupled ocean‐atmosphere system may have acted as a regional amplifier of global climate variability. Plain Language Summary: We use a sedimentary record from the northwest Pacific Ocean to assess the sensitivity of regional sediment transport dynamics to orbital forcing over the last 230 thousand years. By combining the sedimentological records with climate model simulations, we suggest that changes in sediment transport could have resulted from obliquity‐scale changes in atmospheric climatic modes, and specifically the position of the Aleutian Low. Moreover, we found a shift in the location of intermediate water formation during the Last Glacial Maximum, which may have been related to a strengthened Siberian High. This coupled ocean‐atmosphere system represents a potential amplifier of climate variability, such that improved constraints on its past behavior could provide insight into how climatic signals are transferred between regional and global scales. Key Points: Source‐to‐sink studies in the subarctic Pacific Ocean based on geochemical, clay mineralogic and environmental magnetic proxiesThe glacial/interglacial transition can be interpreted to be resulted from atmospheric climatic modes induced by Aleutian low‐forcingThis ocean‐atmosphere response is an amplifying feedback mechanism within the climate system [ABSTRACT FROM AUTHOR]

Two‐electron reduction of carbene‐supported 9‐bromo‐9‐borafluorenes with excess KC8, Na, or Li‐naphthalenide affords six N‐heterocyclic carbene (NHC)‐ or cyclic(alkyl)(amino) carbene (CAAC)‐stabilized borafluorene anions (3–8)‐the first isolated and structurally authenticated examples of the elusive 9‐carbene‐9‐borafluorene monoanion. The electronic structure, bonding, and aromaticity of the boracyclic anions were comprehensively investigated via computational studies. Compounds 5 and 8 react with metal halides via salt elimination to give new B‐E (E=Au, Se, Ge)‐containing materials (9–12). Upon reaction with diketones, the carbene ligand cleanly dissociates from 5 or 8 to yield new B‐O containing spirocycles (13–14) that cannot be easily obtained using "normal" valent borafluorene compounds. Collectively, these results support the notion that carbene‐stabilized monoanionic borafluorenes may serve as a new platform for the one‐step construction of higher‐value boracyclic materials. [ABSTRACT FROM AUTHOR]

A common feature of d‐ and p‐block elements is that they participate in multiple bonding. In contrast, the synthesis of compounds containing homo‐ or hetero‐nuclear multiple bonds involving s‐block elements is extremely rare. Herein, we report the synthesis, molecular structure, and computational analysis of a beryllium imido (Be=N) complex (2), which was prepared via oxidation of a molecular Be0 precursor (1) with trimethylsilyl azide Me3SiN3 (TMS‐N3). Notably, compound 2 features the shortest known Be=N bond (1.464 Å) to date. This represents the first compound with an s‐block metal‐nitrogen multiple bond. All compounds were characterized experimentally with multi‐nuclear NMR spectroscopy (1H, 13C, 9Be) and single‐crystal X‐ray diffraction studies. The bonding situation was analyzed with density functional theory (DFT) calculations, which supports the existence of π‐bonding between beryllium and nitrogen. [ABSTRACT FROM AUTHOR]

The ln(Zr/Rb) count ratio derived from X‐ray fluorescence (XRF) core scanning holds potential as a high‐resolution tracer for grain‐size variations of glaciomarine sediments, and hence current strength. To evaluate this approach, we conducted high‐resolution grain‐size measurements, together with Rb and Zr measurements by XRF core scanning and inductively coupled plasma‐mass spectrometry (ICP‐MS), on a series of sediment cores from different regions of the Southern Ocean. Downcore changes of the ln(Zr/Rb) count ratio from XRF core scanning are consistent with Zr/Rb concentration ratios derived from ICP‐MS analyses, even though Rb and Zr counts deviate significantly from concentrations due to specimen and matrix effects. The ln(Zr/Rb) count ratio displays discrepancies with the bulk mean grain‐size, but correlates well with the mean grain‐size of the sediment fractions that do not include unsorted sand delivered by ice‐rafting. These observations are supported by evidence from a grain‐size separation experiment, which indicates that Zr and Rb are concentrated in different grain‐size fractions. Consistent with its lack of sensitivity to coarse grain‐size fractions derived from ice‐rafting, the ln(Zr/Rb) ratio records similar trends to the sortable silt percent (SS%) and sortable silt mean (SS¯) grain‐size. Universal gradients exist in plots of SS% versus ln(Zr/Rb), and SS¯ versus ln(Zr/Rb), such that the ln(Zr/Rb) ratio provides a convenient way to estimate the magnitude of changes in SS% and SS¯. Overall, our results support the use of the ln(Zr/Rb) ratio as an indicator of bottom current strength in cases where the sediment is current‐sorted. Key Points: Ln(Zr/Rb) co‐varies with the iceberg rafted debris‐corrected mean grain‐size of glaciomarine sediments from the Southern OceanLn(Zr/Rb) reflects changes in bottom current strength if the sediment is bottom current‐sortedConstant gradients observed in plots of ln(Zr/Rb) versus SS%, and ln(Zr/Rb) versus SS¯ [ABSTRACT FROM AUTHOR]

The 9‐borataphenanthrene anion is easily accessed by deprotonation of a 9,10‐dihydro‐9‐boraphenanthrene and its diverse reactivity is investigated. Alkylation occurs at the carbon atom adjacent to boron, and room temperature hydroboration occurs across the B=C bond. The π‐manifold of the central BC5 ring coordinates to chromium in an η6 fashion while only the B=C unit binds η2 to gold, indicating versatility of the 9‐borataphenanthrene anion as a ligand. Supporting calculations rationalize the reactivity and aromaticity is corroborated by nucleus‐independent chemical shift (NICS) indices. [ABSTRACT FROM AUTHOR]

The [Ir(df‐ppy)2(ptb)]+ complex (where df‐ppy=2‐(2,4‐difluorophenyl)pyridine anion; ptb=1‐benzyl‐1,2,3‐triazol‐4‐ylpyridine) has previously been shown to be a promising blue luminophore for electrogenerated chemiluminescence (ECL). Herein, we examine the ECL of three [Ir(df‐ppy)2(ptb)]+ derivatives (containing df(CF3)‐ppy‐Me, df(CN)‐ppy, or df‐ppy‐CF3 ligands) in comparison with the parent complex. In the annihilation mode, all four complexes exhibited ECL, although the emission from [Ir(df(CN)‐ppy)2(ptb)]+ was weak and red‐shifted from its photoluminescence. The absence of this shift in the corresponding reductive‐oxidation co‐reactant ECL with benzoyl peroxide (BPO), and the very low ECL intensity in oxidative–reductive co‐reactant ECL with tri‐n‐propylamine (TPrA) enables this effect to be ascribed to oxidative degradation. The [Ir(df‐ppy‐CF3)2(ptb)]+ complex gave the greatest ECL intensities of the four [Ir(C∧N)2(ptb)]+ complexes in the annihilation mode and through both co‐reactant pathways, and shows great potential as a blue electrochemiluminophore. In "mixed annihilation" ECL experiments involving the oxidation of Ir(ppy)3 and the reduction of the [Ir(C∧N)2(ptb)]+ complexes, only [Ir(df‐ppy)2(ptb)]+ and [Ir(df(CF3)‐ppy‐Me)2(ptb)]+ elicited the green ECL from Ir(ppy)3*, as the electron‐withdrawing substituents on the other two complexes lower the SOMO energy of the reduced complexes below that required to attain the Ir(ppy)3* excited state upon reaction with [Ir(ppy)3]+. [ABSTRACT FROM AUTHOR]

The synthesis and reactivity study of the first isolable boraphosphaketene, cyclic(alkyl)(amino) carbene (CAAC)‐borafluorene‐P=C=O (2), is described. Photolysis of compound 2 results in the formation of CAAC‐stabilized BP‐doped phenanthryne (3) through tandem decarbonylation, monoatomic phosphide insertion, and ring‐expansion. Notably, while BN‐doped phenanthryne was previously discussed as a reactive intermediate which could not be isolated, the heavier BP‐doped analogue exhibits remarkable solution and solid‐state stability. The reactivity of 2 with stable carbenes was also explored. Addition of CAAC to 2 led to migration of the original CAAC ligand from boron to phosphorus and coordination of the added CAAC to carbon, affording compound 4. Reaction of 1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene (NHC) with 2 resulted in N−C bond activation to give the unusual spiro‐heterocyclic compound (5). [ABSTRACT FROM AUTHOR]

N‐Heterocyclic carbene (NHC)‐ and cyclic (alkyl)(amino)carbene (CAAC)‐stabilized borafluorene radicals have been isolated and characterized by elemental analysis, single‐crystal X‐ray diffraction, UV/Vis absorption, cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, and theoretical studies. Both the CAAC–borafluorene radical (2) and the NHC–borafluorene radical (4) have a considerable amount of spin density localized on the boron atoms (0.322 for 2 and 0.369 for 4). In compound 2, the unpaired electron is also partly delocalized over the CAAC ligand carbeneC and N atoms. However, the unpaired electron in compound 4 mainly resides throughout the borafluorene π‐system, with significantly less delocalization over the NHC ligand. These results highlight the Lewis base dependent electrostructural tuning of materials‐relevant radicals. Notably, this is the first report of crystalline borafluorene radicals, and these species exhibit remarkable solid‐state and solution stability. [ABSTRACT FROM AUTHOR]

The first examples of N‐heterocyclic carbene (NHC) and cyclic(alkyl)(amino) carbene (CAAC) stabilized borepinium and borafluorenium heterocycles are reported herein. The optical properties of the heterocyclic borenium cations were tuned by varying the Lewis base and by changing the number of atoms in the ring. More importantly, functionalizing the cationic boron ring system in the NHC‐borafluorenium cation affords a temperature‐sensitive molecule with reversible colorimetric "turn off/turn on" properties in solution. Notably, this is the first report of thermochromism in these cationic species. This property, which is mediated by an intermolecular boron–oxygen bond equilibrium, was examined in detail by X‐ray crystallography, variable temperature‐UV/Vis absorption spectroscopy (VT‐UV/Vis), and density functional theory (DFT). [ABSTRACT FROM AUTHOR]

Although ultimately not isolable for X‐ray structural characterization, the free perfluorinated trityl cation was shown to be observable in neat triflic acid, which represents milder conditions than previous reports of this cation in "magic acid" or oleum. A triflate‐bound species could be generated in organic solvents using stoichiometric amounts of triflic acid and was shown to be synthetically viable for hydride abstraction from Et3SiH. It was demonstrated that the para‐position on the ‐C6F5 rings is the primary point of attack for decomposition of the cation. Blast from the past. A triflate bound derivative of the perfluorinated trityl cation can be generated from triflic acid in organic solvent at −20 °C and used as a hydride acceptor. The free cation can also be observed in neat triflic acid. Attack on the para‐carbon by nucleophiles is the primary mode of decomposition of the cation. [ABSTRACT FROM AUTHOR]

SuFEx is a new‐generation click chemistry transformation that exploits the unique properties of S−F bonds and their ability to undergo near‐perfect reactions with nucleophiles. We report here the first SuFEx‐based procedure for the efficient synthesis of pharmaceutically important triflones and bis(trifluoromethyl)sulfur oxyimines from sulfonyl fluorides and iminosulfur oxydifluorides, respectively. The new process involves rapid S−F exchange with trifluoromethyltrimethylsilane (TMSCF3) upon activation by potassium bifluoride in anhydrous DMSO. The reaction tolerates a wide selection of substrates and proceeds under mild conditions without need for chromatographic purification. A tentative mechanism is proposed involving nucleophilic displacement of S−F by the trifluoromethyl anion via a five‐coordinate intermediate. The utility of late‐stage SuFEx trifluoromethylation is demonstrated through the synthesis and selective anticancer properties of a bis(trifluoromethyl)sulfur oxyimine. An expedient SuFEx trifluoromethylation of sulfonyl fluorides and iminosulfur oxyfluorides is described. The efficient S−F exchange with TMSCF3 is initiated by sub‐stoichiometric quantities of bifluoride ion [FHF]− in anhydrous DMSO. The selective anticancer properties of previously inaccessible bis(trifluoromethyl)sulfur oxyimines are also demonstrated. [ABSTRACT FROM AUTHOR]

The reactions of a monomeric borole and a dimeric borole with 2,3‐dimethyl‐1,3‐butadiene and 1,3‐cyclohexadiene were investigated. The monomeric borole reacted at ambient temperature whereas heat was required to crack the dimer to form the monomer and induce reactivity. 2,3‐Dimethyl‐1,3‐butadiene reacts to give diverse products resulting from a cycloaddition process with the B−C moiety of the boroles acting as a dienophile, followed by rearrangements to furnish bicyclic species. For 1,3‐cyclohexadiene, a [4+2] process is observed in which 1,3‐cyclohexadiene serves as the dienophile and the boroles as the diene partner. The experimental results are corroborated with mechanistic theoretical calculations that indicate boroles can serve as either a diene or dienophile in cycloaddition reactions with dienes. Diene to be a Dienophile: Reactions of boroles with 2,3‐dimethyl‐1,3‐butadiene and 1,3‐cyclohexadiene were investigated. The experimental results are corroborated with mechanistic theoretical calculations that indicate boroles can serve as either a dienophile (2,3‐dimethyl‐1,3‐butadiene) or a diene (1,3‐cyclohexadiene) in cycloaddition reactions with dienes. [ABSTRACT FROM AUTHOR]

The endocyclic ring expansion of N‐heterocyclic carbene (NHC) rings containing one N atom and one P, N, C, O or S heteroatom has been investigated in a computational study. Ring expansion was determined to follow a common pathway, leading to a final expanded six‐membered ring that was predicted to be thermodynamically stable for all heterocycles. However, reactivity is driven by kinetics with ring‐expansion reactivity not expected for the P/NHC and C/NHC (cAAC) containing heterocycles due to large barriers for ring‐expansion. In contrast, ring expansion is predicted to be feasible for N‐heterocyclic carbenes containing an O (O/NHC) or S (S/NHC) heteroatom, with insertion into the O−C and S−C bond favoured over insertion into the N−C bond, respectively. This study rings true: A theoretical investigation of N‐heterocyclic carbenes with mixed heteroatoms indicates that previously unobserved hydride ring expansion of NHCs containing an O or S atom may occur. Insertion into the O−C or S−C bond is favoured over N−C insertion. Ring expansion is not expected with NHCs containing a P heteroatom. [ABSTRACT FROM AUTHOR]

We report the first example of an alkene with two carbon-bound substituents (imidazole and imidazolium rings) where the Z-isomer has a greater thermodynamic stability than the E-isomer which persists in both the gas phase and in solution. Theoretical calculations, solution fluorescence spectroscopy and gas-phase ion mobility mass spectrometry studies confirm the preference for the Z-isomer, the stability of which is traced to a non-covalent interaction between the imidazole lone pair and the imidazolium ring. [ABSTRACT FROM AUTHOR]

The endocyclic ring expansion of N-heterocyclic carbene (NHC) rings by transition metal (group 12) and main group (group 13-16) element hydrides has been investigated in a computational study. In addition to previously reported insertion reactivity with Si, B, Be and Zn, similar reactivity is predicted to be feasible for heavier group 13 elements (Al, Ga, In, Tl), with the reaction barriers for Al-Tl calculated to be lower than for boron. Insertion is not expected with group 15-16 element hydrides, as the initial adduct formation is thermodynamically unfavorable. The reaction pathway with group 12 hydrides is calculated to be more favorable with two NHCs rather than a single NHC (analogous to Be), however hydride ring insertion with metal dihydrides is not feasible, but rather a reduced NHC is thermodynamically favored. For group 14, ring-insertion reactivity is predicted to be feasible with the heavier dihydrides. Trends in reactivity of element hydrides may be related to the protic or hydridic character of the element hydrides. [ABSTRACT FROM AUTHOR]

We examine the electrogenerated chemiluminescence (ECL) of three Ir( [ABSTRACT FROM AUTHOR]

Experimental studies suggest that the compound (NHCbz)2C2H2 can be considered as a complex of a distorted acetylene fragment which is stabilised by benzoannelated N-heterocyclic carbene ligands (NHCbz)→(C2H2)←(NHCbz). A quantum chemical analysis of the electronic structures shows that the description with dative bonds is more favourable than with electron-sharing double bonds (NHCbz)=(C2H2)=(NHCbz). [ABSTRACT FROM AUTHOR]

Incorporating phenylpyridine- and triazolylpyridine-based ligands decorated with methylsulfonate or tetraethylene glycol (TEG) groups, a series of iridium(III) complexes has been created for green and blue electrogenerated chemiluminescence under analytically useful aqueous conditions, with tri- n-propylamine as a coreactant. The relative electrochemiluminescence (ECL) intensities of the complexes were dependent on the sensitivity of the photodetector over the wavelength range and the pulse time of the applied electrochemical potential. In terms of the integrated area of corrected ECL spectra, with a pulse time of 0.5 s, the intensities of the IrIII complexes were between 18 and 102 % that of [Ru(bpy)3]2+ (bpy=2,2′-bipyridine). However, when the intensities were measured with a typical bialkali photomultiplier tube, the signal of the most effective blue emitter, [Ir(df-ppy)2(pt-TEG)]+ (df-ppy=2-(2,4-difluorophenyl)pyridine anion, pt-TEG=1-(2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethyl)-4-(2-pyridyl)-1,2,3-triazole), was over 1200 % that of the orange-red emitter [Ru(bpy)3]2+. A combined experimental and theoretical investigation of the electrochemical and spectroscopic properties of the IrIII complexes indicated that the greater intensity from [Ir(df-ppy)2(pt-TEG)]+ relative to those of the other IrIII complexes resulted from a combination of many factors, rather than being significantly favored in one area. [ABSTRACT FROM AUTHOR]

Photoredox catalysis with the use of a stable, reusable silica-bound chromophore was applied to the intramolecular cyclization of a series of 2-benzylidenehydrazinecarbothioamides to give 5-phenyl-1,3,4-thiadiazol-2-amines. The catalyst was readily prepared by carbodiimide-mediated coupling of commercially available amine-functionalized silica beads to a carboxylic acid functionalized ruthenium complex. The immobilized catalyst was readily removed from the reaction product by filtration and was used eight times without loss of catalytic activity. This simple, safe, and practical method is an attractive alternative to conventional procedures. [ABSTRACT FROM AUTHOR]

The attempted synthesis of NHC-stabilized dicarbon (NHCCCNHC) through deprotonation of a doubly protonated precursor ([NHCCHCHNHC]2+) is reported. Rather than deprotonation, a clean reduction to NHCCHCHNHC is observed with a variety of bases. The apparent resistance towards deprotonation to the target compound led to a reinvestigation of the electronic structure of NHC→CC←NHC, which showed that the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) gap is likely too small to allow for isolation of this species. This is in contrast to the recent isolation of the cyclic alkylaminocarbene analogue (cAACCCcAAC), which has a large HOMO-LUMO gap. A detailed theoretical study illuminates the differences in electronic structures between these molecules, highlighting another case of the potential advantages of using cAAC rather than NHC as a ligand. The bonding analysis suggests that the dicarbon compounds are well represented in terms of donor-acceptor interactions L→C2←L (L=NHC, cAAC). [ABSTRACT FROM AUTHOR]

A computational study has been carried out to examine the feasibility of generating a simple monocyclic cyclopentadienyl cation that may be sufficiently stable to isolate and handle at ambient temperatures. Using judicious placement of electron-withdrawing groups (CF3) about the ring we have identified a derivative that may approach the stability of isolobal (and isolatable) borole rings, as evaluated by HOMO-LUMO and singlet-triplet gaps. These Cp+ derivatives may therefore be an attractive target for synthetic isolation. [ABSTRACT FROM AUTHOR]

The relative Lewis acidities of a series of known, unknown and observed but unstable halogenated derivatives of the trityl cation have been probed in a computational study. The Lewis acidity was investigated from hydride, fluoride and methide affinities. The results indicate that the perhalogenated trityl cation [C(C6F5)3]+ is a desirable synthetic target, especially in the modern age of weakly coordinating anions. Our results also indicate that the stable [C(C6Cl5)3]+ cation may be an equally interesting Lewis acid. [ABSTRACT FROM AUTHOR]

Compared to tris(2-phenylpyridine)iridium(III) ([Ir(ppy)3]), iridium(III) complexes containing difluorophenylpyridine (df-ppy) and/or an ancillary triazolylpyridine ligand [3-phenyl-1,2,4-triazol-5-ylpyridinato (ptp) or 1-benzyl-1,2,3-triazol-4-ylpyridine (ptb)] exhibit considerable hypsochromic shifts (ca. 25-60 nm), due to the significant stabilising effect of these ligands on the HOMO energy, whilst having relatively little effect on the LUMO. Despite their lower photoluminescence quantum yields compared with [Ir(ppy)3] and [Ir(df-ppy)3], the iridium(III) complexes containing triazolylpyridine ligands gave greater electrogenerated chemiluminescence (ECL) intensities (using tri- n-propylamine (TPA) as a co-reactant), which can in part be ascribed to the more energetically favourable reactions of the oxidised complex (M+) with both TPA and its neutral radical oxidation product. The calculated iridium(III) complex LUMO energies were shown to be a good predictor of the corresponding M+ LUMO energies, and both HOMO and LUMO levels are related to ECL efficiency. The theoretical and experimental data together show that the best strategy for the design of efficient new blue-shifted electrochemiluminophores is to aim to stabilise the HOMO, while only moderately stabilising the LUMO, thereby increasing the energy gap but ensuring favourable thermodynamics and kinetics for the ECL reaction. Of the iridium(III) complexes examined, [Ir(df-ppy)2(ptb)]+ was most attractive as a blue-emitter for ECL detection, featuring a large hypsochromic shift ( λmax=454 and 484 nm), superior co-reactant ECL intensity than the archetypal homoleptic green and blue emitters: [Ir(ppy)3] and [Ir(df-ppy)3] (by over 16-fold and threefold, respectively), and greater solubility in polar solvents. [ABSTRACT FROM AUTHOR]

Genotype-phenotype correlation in von Hippel-Lindau disease with retinal angiomatosis. It would be fitting to add her name so that it is von Hippel-Lindau-Chew Disease, caused by the I VHLC i gene. While we're at it, let's change Best Disease to Adams disease and rename the I BEST1-4 i genes the I ADAMS1-4 i genes. [Extracted from the article]

The photophysical and related properties of platinum(II) Schiff base complexes can be finely and predictably tuned over a wide range of wavelengths by small and easily implemented changes to ligand structure. A series of such complexes, differing only in the number and positioning of methoxy substituents on the phenoxy ring, were synthesised and their photophysical, electrochemical and electrochemiluminescent (ECL) properties investigated. Theoretical calculations were performed in order to gain further insight into the relationship between structure and properties in these materials. By positioning methoxy groups para and/or ortho to either the imine or the oxygen group on the ligand, electron density could be directed selectively toward the LUMO or HOMO as required. This allowed the emission colour (both photoluminescent and electrochemiluminescent) to be tuned over a wide range between 587 and 739 nm. The variation in orbital energies was also manifested in the positions of the absorption bands and the redox properties of the complexes, as well as in the NMR shifts for the uncoordinated ligands. All reported complexes displayed intense electrochemiluminescence (ECL), which could be initiated either by annihilation or co-reactant pathways. The relationship between the electrochemical and photophysical properties and the efficiency of the ECL is discussed. For two of the complexes solid-state ECL could be generated from electrodeposited layers of the complex. [ABSTRACT FROM AUTHOR]

The study of ligand stabilised mono- and diatomic zero oxidation state complexes is a young and fascinating topic. This area merges the fields of low-oxidation-state main-group chemistry, homoatomic multiple bonding and fundamental coordination chemistry. As with a great deal of recent coordination chemistry within the d-block, carbene ligands are clearly the star of the show, highlighting their importance within the p-block as well. This Minireview focuses on the significant developments of the past two years. [ABSTRACT FROM AUTHOR]

The molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) and MM-generalized-Born surface area (MM-GBSA) approaches are commonly used in molecular modeling and drug design. Four critical aspects of these approaches have been investigated for their effect on calculated binding energies: (1) the atomic partial charge method used to parameterize the ligand force field, (2) the method used to calculate the solvation free energy, (3) inclusion of entropy estimates, and (4) the protonation state of the ligand. HIV protease has been used as a test case with six structurally different inhibitors covering a broad range of binding strength to assess the effect of these four parameters. Atomic charge methods are demonstrated to effect both the molecular dynamics (MD) simulation and MM-PB(GB)SA binding energy calculation, with a greater effect on the MD simulation. Coefficients of determination and Spearman rank coefficients were used to quantify the performance of the MM-PB(GB)SA methods relative to the experimental data. In general, better performance was achieved using (i) atomic charge models that produced smaller mean absolute atomic charges (Gasteiger, HF/STO-3G and B3LYP/cc-pVTZ), (ii) the MM-GBSA approach over MM-PBSA, while (iii) inclusion of entropy had a slightly positive effect on correlations with experiment. Accurate representation of the ligand protonation state was found to be important. It is demonstrated that these approaches can distinguish ligands according to binding strength, underlining the usefulness of these approaches in computer-aided drug design. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]