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 B–B 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,N′-di-isopropyl carbodiimide and by density functional theory

Contrasting reactivity of B–Cl and B–H 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: B–Cl activation proceeds via nucleophilic displacement of Cl−, while B–H activation would entail high energy concerted bond cleavage

Uranyl oxo activation and functionalization by metal cation coordination

International audienceThe oxo groups in the uranyl ion [UO$_2$]$^{2+}$ , one of many oxo cations formed by metals from across the periodic table—are 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 ‘Pacman’ 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 C–H 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, “Pacman” 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 MgN″2 (N″ = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg functionalized as a result of Mg−N bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(N″)Cl] favor the formation of weaker U−O−Zn 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 man’s fear, glory and greed on war and peace, not for his views on the bearing of men’s 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

L’affaire serait simple si, comme il pourrait le sembler de prime abord, la question du statut du nom dans la grammaire générale de Condillac s’inscrivait dans la droite ligne de l’héritage de Port-Royal. Seule se trouverait concernée alors, à l’intérieur de la grammaire que le Cours d’études pour l’instruction du Prince de Parme désigne comme « l’art de parler », la place spécifiquement dévolue au nom lorsque la classification des mots est réglée par la considération des principaux modes de ..

Les mots, les idées, la représentation. Genèse de la définition du signe dans la Logique de Port-Royal

L’addition, dans la cinquième édition en 1683 de La Logique ou L’Art de penser, d’un chapitre consacré à la définition générale du signe et de plusieurs chapitres relevant spécifiquement d’une analyse des signes linguistiques, a été parfois interprétée comme une apparition tardive du “problème du langage” dans le traité d’Arnauld et Nicole. Parce que la plupart de ces chapitres supplémentaires sont la transposition de passages auparavant destinés dans la Perpétuité de la foi (1669-1674) à réfuter le sens calviniste de Ceci est mon corps, on a été enclin à attribuer l’importance de la question du signe et du “problème du langage” dans l’édition de 1683 à une origine théologique. J’essaie au contraire de montrer que, dès la première édition de L’Art de penser en 1662, la problématisation des écarts des expressions linguistiques avec une correspondance terme à terme entre les mots et les idées a été indissociable pour Port-Royal de l’analyse des opérations de l’esprit. Selon moi, dans la Perpétuité de la foi, la critique du sens calviniste de la formule eucharistique constitue elle-même une application de cette analyse logique du langage : les passages incorporés ensuite dans L’Art de penser sont dans le prolongement des réflexions de 1662 sur les difficultés d’adéquation entre le dire et le vouloir-dire. Je montre pour finir que la définition générale du signe à Port-Royal suppose une restructuration de la définition augustinienne du De doctrina christiana, et fonde en 1683 une identification de la relation de signification linguistique à un rapport de représentation des mots aux idées, qui vient redoubler le rapport de représentation des idées aux choses établi en 1662.The addition to the fifth edition (1683) of La Logique ou L’Art 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 “problem of language” in the Logique. Because most of these supplementary chapters had been patched together from passages copied from the Perpétuité de la foi (1669-1674), this has led commentators to attribute the later foregrounding of the “problem of language” in the Logique to a semiotic analysis that arises in Port Royal’s anti-Calvinist polemic over the meaning of “Hoc est corpus meum”. Against this reading, in the first part of my essay, I try to show that from the first edition of L’Art 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 speaker’s meaning. The aim of the logical analysis of L’Art 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 Perpétuité 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 L’Art de penser from the Perpétuité 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 Augustine’s 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