312 research outputs found
Catalytic Access to Diastereometrically Pure Four‐ and Five‐Membered Silyl‐Heterocycles Using Transborylation
Full text link: Silyl-heterocycles offer a unique handle to expand and explore chemical space, reactivity, and functionality. The shortage of catalytic methods for the preparation of diverse and functionalized silyl-heterocycles however limits widespread exploration and exploitation. Herein the borane-catalyzed intramolecular 1,1-carboboration of silyl-alkynes has been developed for the synthesis of 2,3-dihydrosilolyl and silylcyclobut-2-enyl boronic esters. Successful, catalytic carboboration has been achieved on a variety of functionally diverse silyl-alkynes, using a borane catalyst and transborylation-enabled turnover. Mechanistic studies, including 13C-labelling, computational studies, and single-turnover experiments, suggest a reaction pathway proceeding by 1,2-hydroboration, 1,1-carboboration, and transborylation to release the alkenyl boronic ester product and regenerate the borane catalyst
Intermolecular Sp<sup>3</sup>C─H Metalation of Non‐Nucleophilic Brønsted Bases Using Simple Lewis Acids
No full text2,6‐Di‐tert‐butyl substituted pyridines (tBu2‐py) are widely used non‐nucleophilic Brønsted bases. Their ubiquity is due to their highly hindered basic site and chemically robust nature. Herein we report that simple M2X6 Lewis acids (M═Al or Ga, X═Cl, Br or I) effect intermolecular sp3C─H metalation of t Bu2‐py bases under mild conditions. The sp3C─H metalated products can be converted in situ into ─BPin, ─iodo, ─bromo and ─hydroxy derivatives for further elaboration. Mechanistic investigations indicate that: i) a frustrated Lewis pair effects sp3C─H heterolysis to form the C─M bond and a protonated pyridine; ii) C─H metalation requires singly halide‐bridged super‐electrophilic M2X6 dimers for sufficiently low barriers. Finally, sp3C─H metalation using M2X6 is not limited to t Bu2‐py bases. Thus, it is important to be aware of this facile sp3C─H functionalisation when using a range of non‐nucleophilic Brønsted bases
Group 13 exchange for catalytic turnover
Full text linkTransition metals are able to undergo redox-active processes, such as oxidative addition and reductive elimination with carbon-element bonds. These two fundamental steps have allowed for the majority of metal-catalysed processes to take place by providing access to multiple oxidation states. Precious metals, such as palladium, platinum, iridium, rhodium, and ruthenium, dominate transition metal catalysis due to their wide applicability and highly tuneable ligands. However, these metals can be toxic and have low abundance in the Earth’s crust, leading to high costs and difficult purification.
Group 13 elements are an attractive alternative to transition metals in catalysis due to their lower toxicity and cost. Group 13 elements are electron-deficient, giving them unique reactivity within the main-group; however, their synthetic utility has been limited to stoichiometric processes. Group 13 elements do not have access to empty d-orbitals, so cannot undergo the same redox-active processes that transition metals can, therefore their applications in catalysis are limited to redox-neutral processes. Therefore, new methods of catalytic turnover are required for the application of group 13 elements in catalysis. Group 13 exchange has been developed as a redox-neutral process for catalytic turnover, whereby classically stoichiometric reactions have been rendered catalytic. Group 13 exchange has been applied to the aluminium-catalysed C‒H borylation of alkynes with HBpin using a tethered Al/N Lewis pair, which shut down the competitive alkyne hydroboration pathway.
Transborylation, group 13 exchange between two boron atoms, has provided access to metal-free catalytic systems by extending traditional stoichiometric borane-mediated reactions. Transborylation has been applied to borane-catalysed hydroboration and reduction, classic stoichiometric reactions that have been rendered catalytic. This work has successfully extended the catalogue of transborylation-mediated catalysis: borane-catalysed C‒F arylation and esterification of alkyl fluorides demonstrated excellent functional group tolerance across a wide range of examples. The borane-catalysed asymmetric hydroboration of alkenes showed promise, with moderate yields and enantioselectivities, and improved the synthesis of chiral borane reagents. The borane-catalysed intramolecular 1,1-carboboration of silylalkynes gave access to a variety of silolenyl boronic esters and was the first example of a borane-catalysed carboboration reaction
The influence of social context on reward-processing and associated neural signals
No full textHuman decision-making is often motivated by a pursuit of valued goals, such as food and money. Such pursuits can be influenced not only by the actual value of the goal (e.g., 10), but also importantly by the social context in which they occur (e.g., with a close peer vs. with a business colleague). The aim of this dissertation was to characterize how social information affects the subjective and neural representations of reward-processing. Neural structures within corticobasal ganglia loops support reward-processing and motivated behavior in part by coding value signals for expected and experienced outcomes, as well as the actions that lead to them. However, most day-to-day experiences occur within varying social contexts. We may thus place higher value on social outcomes such as approval or acceptance, particularly from members of our social networks (e.g., close friends). It remains to be seen how information regarding social network may modulate reward-processing. A novel manipulation of social network was applied to an established reward-processing paradigm such that achieved outcomes were experienced with a close friend (in-network), a confederate (out-of- network), or a non-social entity. Across cooperative and competitive contexts, social network significantly modulated the subjective experience of outcome value and associated computations generated in reward circuitry. To further explore how the effects of social context on reward-processing can modulate behavior, we employed an economic paradigm––the trust game––to investigate learning of partner reputation (e.g., will s/he reciprocate my generosity). We examined the role of prior social impressions formed from direct experience with unknown fictional others in an unrelated domain on subsequent trust game interactions with these same partners. We subsequently applied our social network manipulation to the trust game to investigate how real-life experience informs behavior in trust interactions. In both contexts, previous social impressions significantly influenced participants’ trust decisions. Further, the ability to update beliefs about partner reputation relied on learning-related outcome value signals in neural reward circuitry. In sum, these studies extend the current understanding of reward-processing, demonstrating that the value of a reward is subject to the strong influence of the social context in which it is experienced.Ph. D.Includes bibliographical referencesIncludes vitaby Dominic Stephen Farer
Gendering the Diaspora: Zimbabwean Migrants in Britain
Full text linkThis article analyses the performative and lived realities of the Zimbabwean diaspora in Britain. The author explores the way in which both public and private spaces of the diaspora are important arenas in the construction and reconstruction of gendered identities. It is based on multisited ethnography, comprising 33 in-depth interviews and participant observation in four research sites, and draws upon concepts of diaspora and transnationalism as theoretical and analytical frameworks. The findings suggest that the challenges to patriarchal traditions in the hostland in terms of women's primary migrant status and financial autonomy, the different labour market experiences of men and women, and egalitarian laws have caused tensions and conflict within diaspora households. The article examines how men use religious and social spaces, which provide for the affirmation of more traditional roles and relations, as a form of public resistance to changes happening within the domestic sphere
Group 13 exchange and transborylation in catalysis
Full text linkCatalysis is dominated by the use of rare and potentially toxic transition metals. The main group offers a potentially sustainable alternative for catalysis, due to the generally higher abundance and lower toxicity of these elements. Group 13 elements have a rich catalogue of stoichiometric addition reactions to unsaturated bonds but cannot undergo the redox chemistry which underpins transition-metal catalysis. Group 13 exchange reactions transfer one or more groups from one group 13 element to another, through σ-bond metathesis; where boron is both of the group 13 elements, this is termed transborylation. These redox-neutral processes are increasingly being used to render traditionally stoichiometric group 13-mediated processes catalytic and develop new catalytic processes, examples of which are the focus of this review
Synthesis of Silyl Heterocycles Using Transborylation
No full textSilicon has been proposed as a nonclassical bioisostere to carbon in a 'silicon-switch' approach, however, the synthesis of complex molecules containing silyl heterocycles is still a significant challenge in preparing 'silicon-switch' molecules. Transborylation, the σ-bond metathesis between two boron species, has been utilized for the synthesis of complex molecules, in an orthogonal approach to transition-metal catalysis. Here, the use of transborylation catalysis for the synthesis of structurally diverse silyl heterocycles is highlighted. 1 Introduction 2 Transborylation in Catalysis 3 Silyl Heterocycles 4 Synthesis of Silyl Heterocycles Using Transborylation 5 Conclusions and Outlook.</p
SAM-Melt_EA v5.0 (R Code)
No full textOverviewThe notebooks in this repository contain R code that has been used to investigate the influence of the Southern Annular Mode (SAM) on surface melt in East Antarctica.This work has been undertaken as part of my PhD with MISI and SAEF at Monash University, where I am supervised by Prof. Andrew Mackintosh, Dr. Felicity McCormack, and Dr. Richard Jones. The work has also been supported by co-author Dr. Christiaan van Dalum (IMAU, Utrecht University).This project uses output from the RACMO2.3p3 regional climate model to identify spatiotemporal variability in the SAM-Melt relationship, and to understand the physical mechanisms responsible for the relationship. An accompanying manuscript is currently under review for publication.Code & InstructionsThis project uses the R programming language and was written using RStudio, on both Windows 10 and MacOS 14.1. It uses the renv package to help with portability / replicability.The code here can also be found on GitHub in the SAM-Melt_EA repository, and is tagged as Version v5.0. See the "README.md" file on GitHub for more information about the project and the repository set-up, plus where to download the necessary raw data. In particular, it is necessary to download the RACMO2.3p3 data, available online at: https://doi.org/10.5281/zenodo.7639053.NOTE: This version of the code (v5.0) makes some minor changes to the formatting of the v4.1 figures following the first stage of the peer review process, and includes more comments and notes in the code.Note: In addition to standard R packages from CRAN, it will be necessary to install 5 packages from my GitHub page. These packages (and the version used in this project) are:polarcm (v0.1.3) eases use of output from the polar regional climate models RACMO and MARterrapin (v0.1.1) spinoff from terra that eases handling dates for spatial datafiguR (v0.1.2) for easy-to-customise figureskulaR (v0.1.5) a wrapper around khroma to ease colour management in plotsdomR (v0.1.5) functions for easing how I approach a project with R</p
A generalization of manifolds with corners
Full text linkIn conventional Differential Geometry one studies manifolds, locally modelled on , manifolds with boundary, locally modelled on , and manifolds with corners, locally modelled on . They form categories . Manifolds with corners have boundaries , also manifolds with corners, with . We introduce a new notion of 'manifolds with generalized corners', or 'manifolds with g-corners', extending manifolds with corners, which form a category with . Manifolds with g-corners are locally modelled on for a weakly toric monoid, where for . Most differential geometry of manifolds with corners extends nicely to manifolds with g-corners, including well-behaved boundaries . In some ways manifolds with g-corners have better properties than manifolds with corners; in particular, transverse fibre products in exist under much weaker conditions than in . This paper was motivated by future applications in symplectic geometry, in which some moduli spaces of -holomorphic curves can be manifolds or Kuranishi spaces with g-corners (see the author arXiv:1409.6908) rather than ordinary corners. Our manifolds with g-corners are related to the 'interior binomial varieties' of Kottke and Melrose in arXiv:1107.3320
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