Paire de Lewis

Résumé

vignette|Diagrammes d'orbitales moléculaires illustrant la liaison covalente (à gauche) et la liaison covalente polaire (à droite) dans une molécule diatomique. Dans les deux cas, une liaison est créée par la formation d'un doublet d'électrons ou paire de Lewis. Une paire de Lewis (ou doublet électronique) est une paire d'électrons ayant des spins opposés et occupant une même orbitale atomique. La paire d'électrons peut constituer soit une liaison covalente soit une paire non-liante, localisée sur une orbitale moléculaire principalement non liante (c'est-à-dire n'influant pas sur la stabilité de l'objet moléculaire), ou son équivalent dans le solide (doublet non engagé). Les paires d'électrons de Lewis jouent un rôle fondamental dans le déroulement de certains processus réactionnels comme les réactions de Grignard, ainsi que dans les propriétés mécaniques de certains matériaux. Notes et références Voir aussi

Acide de Lewis
Base de Lewis
Configuration él

Source officielle

https://fr.wikipedia.org/wiki/Paire_de_Lewis

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The immobilization of molecular catalysts imposes spatial constraints on their active site. We reveal that in bifunctional catalysis such constraints can also be utilized as an appealing handle to boost intrinsic activity through judicious control of the active site geometry. To demonstrate this, we develop a pragmatic approach, based on nonlinear scaling relationships, to map the spatial arrangements of the acid–base components of frustrated Lewis pairs (FLPs) to their performance in the catalytic hydrogenation of CO2. The resulting activity map shows that fixing the donor–acceptor centers at specific distances and locking them into appropriate orientations leads to an unforeseen many-fold increase in the catalytic activity of FLPs compared to their unconstrained counterparts.

2022

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Tetrel Lewis acids are a prospective alternative to commonly employed neutral boranes in frustrated Lewis pair (FLP) chemistry. While cationic tetrylium Lewis acids, being isolobal and iso(valence)electronic, are a natural replacement to boranes, neutral tetrel Lewis acids allude as less trivial options due to the absence of a formally empty p orbital on the acceptor atom. Recently, a series of intramolecular geminal FLPs (C2F5)(3)E-CH2-P(tBu)(2) (E = Si, Ge, Sn) featuring neutral tetrel atoms as acceptor sites has been reported for activation of small molecules including H-2. In this work, through density functional theory computations, we elucidate the general mechanistic picture of H-2 activation by this family of FLPs. Our findings reveal that the acceptor atom derives the required Lewis acidity utilizing the antibonding orbitals of its adjacent bonds with the individual contributions depending on the identity of the acceptor and the donor atoms. By varying the identity of the Lewis acid and Lewis base sites and attached substituents, we unravel their interplay on the energetics of the H-2 activation. We find that switching the donor site from P to N significantly affects the synchronous nature of the bond breaking/formations along the reaction pathway, and as a result, N-bearing FLPs have a more favorable H-2 activation profile than those with P. Our results are quantitatively discussed in detail within the framework of the activation-strain model of reactivity along with the energy-decomposition analysis method. Finally, the reductive elimination decomposition route pertinent to the plausible extension of the H-2 activation to catalytic hydrogenation by these FLPs is also examined.

AMER CHEMICAL SOC2021

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Towards a frustrated Lewis pair-ionic liquid system

Felix Daniel Bobbink, Paul Joseph Dyson, Zhaofu Fei, Gabor Laurenczy, Emilia Paunescu, Florian Gérald Perrin, Rosario Scopelliti

An ionic liquid encompassing a bulky tertiary amine was synthesized and used as a dual solvent-reactant for the formation of a frustrated Lewis pair with tris(pentafluorophenyl) borane, forming a pseudo-frustrated Lewis pair-ionic liquid system. The ionic liquid-LA system is prone to self-ionization, i.e. with the formation of iminium and boron hydride species, which are able to form adducts with CO2. Compared to frustrated Lewis pairs operating in organic solvents of low polarity, more forcing conditions are required for the ionic liquid system. Calculations indicate that the anion of the ionic liquid interacts with the Lewis acidic boron center, hindering reactivity, and rationalizing the low reactivity observed. (C) 2017 Elsevier B.V. All rights reserved.

Elsevier2018

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