58 research outputs found
Easy access to nucleophilic boron through diborane to magnesium boryl metathesis
Organoboranes are some of the most synthetically valuable and widely used intermediates in organic and pharmaceutical chemistry. Their synthesis, however, is limited by the behaviour of common boron starting materials as archetypal Lewis acids such that common routes to organoboranes rely on the reactivity of boron as an electrophile. While the realization of convenient sources of nucleophilic boryl anions would open up a wealth of opportunity for the development of new routes to organoboranes, the synthesis of current candidates is generally limited by a need for highly reducing reaction conditions. Here, we report a simple synthesis of a magnesium boryl through the heterolytic activation of the BâB bond of bis(pinacolato)diboron, which is achieved by treatment of an easily generated magnesium diboranate complex with 4-dimethylaminopyridine. The magnesium boryl is shown to act as an unambiguous nucleophile through its reactions with iodomethane, benzophenone and N,NâČ-di-isopropyl carbodiimide and by density functional theory
Contrasting reactivity of BâCl and BâH bonds at [Ni(IMes)2] to form unsupported Ni-boryls
[Ni(IMes)2] reacts with chloroboranes via oxidative addition to form rare unsupported Ni-boryls. In contrast, the oxidative addition of hydridoboranes is not observed and products from competing reaction pathways are identified. Computational studies relate these differences to the mechanism of oxidative addition: BâCl activation proceeds via nucleophilic displacement of Clâ, while BâH activation would entail high energy concerted bond cleavage
Equatorial ligand substitution by hydroxide in uranyl Pacman complexes of a Schiff-base pyrrole macrocycle
Uranyl oxo activation and functionalization by metal cation coordination
International audienceThe oxo groups in the uranyl ion [UO] , one of many oxo cations formed by metals from across the periodic tableâare particularly inert, which explains the dominance of this ion in the laboratory and its persistence as an environmental contaminant. In contrast, transition metal oxo (M=O) compounds can be highly reactive and carry out difficult reactions such as the oxygenation of hydrocarbons. Here we show how the sequential addition of a lithium metal base to the uranyl ion constrained in a âPacmanâ environment results in lithium coordination to the U=O bonds and single-electron reduction. This reaction depends on the nature and stoichiometry of the lithium reagent and suggests that competing reduction and CâH bond activation reactions are occurring
Control of Oxo-Group Functionalization and Reduction of the Uranyl Ion
yesUranyl complexes of a large, compartmental
N8-macrocycle adopt a rigid, âPacmanâ geometry that stabilizes
the UV oxidation state and promotes chemistry at a single
uranyl oxo-group. We present here new and straightforward
routes to singly reduced and oxo-silylated uranyl Pacman
complexes and propose mechanisms that account for the
product formation, and the byproduct distributions that are
formed using alternative reagents. Uranyl(VI) Pacman
complexes in which one oxo-group is functionalized by a
single metal cation are activated toward single-electron
reduction. As such, the addition of a second equivalent of a
Lewis acidic metal complex such as MgNâł2 (Nâł = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg
functionalized as a result of MgâN bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(Nâł)Cl] favor
the formation of weaker UâOâZn dative interactions, leading to reductive silylation of the uranyl oxo-group in preference to
metalation. Spectroscopic, crystallographic, and computational analysis of these reactions and of oxo-metalated products isolated
by other routes have allowed us to propose mechanisms that account for pathways to metalation or silylation of the exo-oxogroup
On benevolence and love of others
Hobbes is famous for his insights into the impact of manâs fear, glory and greed on war and peace, not for his views on the bearing of menâs benevolence on the commonwealth. Are Hobbesian people even capable of love of others? In the literature, we find two main answers: one view is that Hobbes ruled out the possibility of disinterested benevolence among men; the other is that Hobbes considered actions driven by genuine benevolence possible but uncommon. After reviewing in broad outlines the two above positions, this chapter seeks to demonstrate the claim that Hobbes did not consider relevant to establish if men are capable of genuine benevolence or not, because he maintained that benevolent men can be as inept as egoists in differentiating apparent and real good for themselves and their loved ones and the effect of misguided altruism on the commonwealth is as damaging as the effect of ill-advised egoism.Postprin
Le statut du nom dans la grammaire générale de Condillac
Lâaffaire serait simple si, comme il pourrait le sembler de prime abord, la question du statut du nom dans la grammaire gĂ©nĂ©rale de Condillac sâinscrivait dans la droite ligne de lâhĂ©ritage de Port-Royal. Seule se trouverait concernĂ©e alors, Ă lâintĂ©rieur de la grammaire que le Cours dâĂ©tudes pour lâinstruction du Prince de Parme dĂ©signe comme « lâart de parler », la place spĂ©cifiquement dĂ©volue au nom lorsque la classification des mots est rĂ©glĂ©e par la considĂ©ration des principaux modes de ..
Les mots, les idées, la représentation. GenÚse de la définition du signe dans la Logique de Port-Royal
Lâaddition, dans la cinquiĂšme Ă©dition en 1683 de La Logique ou LâArt de penser, dâun chapitre consacrĂ© Ă la dĂ©finition gĂ©nĂ©rale du signe et de plusieurs chapitres relevant spĂ©cifiquement dâune analyse des signes linguistiques, a Ă©tĂ© parfois interprĂ©tĂ©e comme une apparition tardive du âproblĂšme du langageâ dans le traitĂ© dâArnauld et Nicole. Parce que la plupart de ces chapitres supplĂ©mentaires sont la transposition de passages auparavant destinĂ©s dans la PerpĂ©tuitĂ© de la foi (1669-1674) Ă rĂ©futer le sens calviniste de Ceci est mon corps, on a Ă©tĂ© enclin Ă attribuer lâimportance de la question du signe et du âproblĂšme du langageâ dans lâĂ©dition de 1683 Ă une origine thĂ©ologique. Jâessaie au contraire de montrer que, dĂšs la premiĂšre Ă©dition de LâArt de penser en 1662, la problĂ©matisation des Ă©carts des expressions linguistiques avec une correspondance terme Ă terme entre les mots et les idĂ©es a Ă©tĂ© indissociable pour Port-Royal de lâanalyse des opĂ©rations de lâesprit. Selon moi, dans la PerpĂ©tuitĂ© de la foi, la critique du sens calviniste de la formule eucharistique constitue elle-mĂȘme une application de cette analyse logique du langage : les passages incorporĂ©s ensuite dans LâArt de penser sont dans le prolongement des rĂ©flexions de 1662 sur les difficultĂ©s dâadĂ©quation entre le dire et le vouloir-dire. Je montre pour finir que la dĂ©finition gĂ©nĂ©rale du signe Ă Port-Royal suppose une restructuration de la dĂ©finition augustinienne du De doctrina christiana, et fonde en 1683 une identification de la relation de signification linguistique Ă un rapport de reprĂ©sentation des mots aux idĂ©es, qui vient redoubler le rapport de reprĂ©sentation des idĂ©es aux choses Ă©tabli en 1662.The addition to the fifth edition (1683) of La Logique ou LâArt de penser (1662), first a chapter dedicated to the general definition of a sign, then five chapters specifically relating to an analysis of linguistic signs, has sometimes been interpreted as a belated appearance of the âproblem of languageâ in the Logique. Because most of these supplementary chapters had been patched together from passages copied from the PerpĂ©tuitĂ© de la foi (1669-1674), this has led commentators to attribute the later foregrounding of the âproblem of languageâ in the Logique to a semiotic analysis that arises in Port Royalâs anti-Calvinist polemic over the meaning of âHoc est corpus meumâ. Against this reading, in the first part of my essay, I try to show that from the first edition of LâArt de penser, the analysis of language had been inseparable from the analysis of the operations of the mind. For Port Royal, the central function of the Logique involves resolving all instances of linguistic confusion or equivocation which disturb or prevent grasping the speakerâs meaning. The aim of the logical analysis of LâArt de penser is to train the judgment to understand linguistic expressions that involve gaps and deviations with respect to a model of term by term correspondence between ideas and words. In the second part of the essay, I oppose the thesis that the theorization of sign and signification in the chapters added to the 1683 edition of the Logique depends on the theological dimension of the anti-Calvinist discussion. I show that the critique of the Calvinist conception of the Eucharist as the sign of the absent body of Christ in fact itself constitutes in the PerpĂ©tuitĂ© de la foi an application of the analysis of language proposed in 1662 in the Logique. That which the enlarged edition of 1683 incorporates into LâArt de penser from the PerpĂ©tuitĂ© de la foi thus constitutes the part of the anti-Calvinist controversy that is itself logical, not theological, the extension of the reflections of 1662 on the difficulties of relating that which is said to that which is meant. A third part of the essay is devoted to the construction of the general definition of a sign in the 1683 edition of the Logique. On the one hand, I reconstitute the way in which Port Royal proceeds to a reconstruction of the definition of Augustineâs De doctrina christiana. On the other hand, I show that this general definition grounds an identification of the relation of linguistic signification with a relation of representation between words and ideas, which reduplicates in 1683 the relation of representation of ideas to things established in 1662
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