Ambiphilic Frustrated Lewis Pair Exhibiting High Robustness and Reversible Water Activation: Towards the Metal-Free Hydrogenation of Carbon Dioxide

Rochette, Étienne; Courtemanche, Marc-André; Pulis, Alexander P.; Bi, Weihong; Fontaine, Frédéric‐Georges

doi:10.3390/molecules200711902

Cited by 21 publications

(19 citation statements)

References 53 publications

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“…IV is predicted to exothermically, but endergonically split molecular hydrogen (standard enthalpy and standard Gibbs energy at 298 K are −2.3 and +6.9 kcal mol −1 , respectively, at ωB97XD/6–31++G** level of theory). Experiments showed no reactivity of this compound toward molecular hydrogen, but it was active to split water, formic acid, and methanol . It is expected, that stronger LAs will facilitate hydrogen splitting by such FLP.…”

Section: Introductionmentioning

confidence: 92%

“…In most of the experimentally and computationally studied cases, group 13 LA adopts planar configuration (sum of valence angles close to 360°: 359.1 in IV , 354.7 in V ). Only in case of II, the boron atom is pyramidalized (the sum of valence C‐B‐C angles in related THF‐boroadamantane adduct is 330.9(1) or 331.4(2)); however, this LA has no electron withdrawing groups and require strong N ‐heterolytic carbene as an LB center.…”

Section: Introductionmentioning

confidence: 99%

“…Compound 1‐(9‐borabicyclo[3.3.1]nonane)‐2‐(2,2,6,6‐tetramethylpiperidine)‐C 6 H 4 IV , designed and synthesized by Rochette et al, features benzene bridge, B…N distance of 3.053(1) Å with planar B center (sum of internal CBC angles 359.1(1)°) and flexible BC bond with a benzene spacer. IV is predicted to exothermically, but endergonically split molecular hydrogen (standard enthalpy and standard Gibbs energy at 298 K are −2.3 and +6.9 kcal mol −1 , respectively, at ωB97XD/6–31++G** level of theory).…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen splitting by pyramidalized 13–15 donor–acceptor cryptands: A computational study

El‐Hamdi

Timoshkin

2019

J Comput Chem

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A series of new donor-acceptor cryptands, where pyramidalized donor (azaadamantane) and acceptor (bora/ala/adamantane) molecules are spatially oriented toward each other and linked via aromatic spacer, are constructed and computationally studied at M06-2X and ωB97X-D levels of theory. Kinetic stability of the perfluorinated boraand ala-adamantane with respect to F migration to group 13 element is demonstrated. The effectiveness of the constructed cryptands, featuring pyramidalized perfluorinated acceptor moieties, in the heterolytic splitting of molecular hydrogen is predicted. Hydrogen splitting is highly exothermic and exergonic and is accompanied by small activation barriers. The most promising candidates for the experimental studies are identified.

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hydrogen splitting by pyramidalized 13–15 donor–acceptor cryptands: A computational study

El‐Hamdi

Timoshkin

2019

J Comput Chem

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“…Althoughw ater activation by FLPs is known [14] and, recently, af ew water-tolerant FLP systems have been reported, [15] mois-ture sensitivity is one of the limiting factorsf or the application of this type of system in many catalytic transformations.D ue to their high acidity, FLPs form water adducts that can be easily deprotonated by soft bases (for example, donor solvents) yielding species inactive for FLP chemistry. [15a,f, 16] Here we report on compound 2, an air-and moisture-stable complex featuring as trong but constrained RhÀN(p-Tol) Lewis acid/base interaction, that is able to activate H 2 O (and D 2 O) in ar eversible manner followinga nF LP reactivity pattern.…”

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confidence: 99%

Reversible Activation of Water by an Air‐ and Moisture‐Stable Frustrated Rhodium Nitrogen Lewis Pair

Carmona

Ferrer

Rodrı́guez

et al. 2019

Chemistry A European J

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“…We were able to synthesize ambiphilic molecule 1-TMP-2-BBN-C6H4 (TMP = 2,2,6,6-tetramethylpiperidinyl; BBN = borabicyclo[3.3.1]nonane, 12) containing endocyclic amine and borane moieties. 35 Interestingly, this molecule is stable in presence of a moderate excess of water and formic acid (Scheme 7). Even if 12 binds these reduction side-products, the reversibility of these processes suggests that catalysis might be accessible.…”

Section: Developing Metal-free Co2 Reduction Catalystsmentioning

confidence: 99%

Ambiphilic Molecules: From Organometallic Curiosity to Metal-Free Catalysts

2018

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Ambiphilic molecules were first used as functional ligands for transition elements, which could enable intriguing organometallic transformations. In the past decade, these intramolecular Lewis pairs, first considered organometallic curiosities, have become staples in organometallic chemistry and catalysis, acting as Z ligands, activating inert molecules using the concept of frustrated Lewis pair (FLP) chemistry, and acting as metal-free catalysts. In this Account, we detail our contribution to this blossoming field of research, focusing on the use of ambiphilic molecules as metal-free catalysts for CO reduction and C-H borylation reactions. A major emphasis is put on the mechanistic investigations we carried out using reactivity studies and theoretical tools, which helped us steer our research from stoichiometric transformations to highly active catalytic processes. We first report the interaction of aluminum-phosphine ambiphilic molecules with carbon dioxide. Although these Lewis pairs can bind CO, a study of the deactivation process in the presence of CO and hydroboranes led us to discover that simple phosphinoborane molecules could act as active precatalysts for the hydroboration of carbon dioxide into methanol precursors. In these systems, the Lewis basic sites interact with the reducing agents rather than with the electrophilic carbon of CO, increasing the nucleophilicity of hydroboranes. Simultaneously, the weak Lewis acids stabilize the oxygen of the gas molecule in the transition state, leading to high reaction rates. Replacing the phosphine by an amine leads to a system enabling CO hydrogenation, albeit only in stoichiometric transformations. Investigation of the protodeborylation deactivation of aminoboranes led us to develop metal-free catalysts for the C-H borylation of heteroarenes. By protecting the Lewis acid sites of these catalysts using fluoride, we were able to synthesize practical, air-stable precatalysts allowing the convenient synthesis of heteroarylboronic esters on a multigram scale. Contrary to general perception of FLP chemistry, we also demonstrated that a significant increase in activity could be obtained by reducing the steric bulk around the active site. These smaller systems exist as stable dimers and are more energetically costly to dissociate into active FLPs, but the approach of the substrate and the C-H activation step are significantly favored compared to the bulkier analogues. An in-depth study of the stability and reactivity of these aminoborane molecules also allowed us to develop a metal-free catalytic S-H bond borylation system, and to report stoichiometric and spontaneous B-B bond formation and Csp-H bond activation processes, highlighting the importance of H release as a thermodynamic driving force in these FLP transformations.

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Ambiphilic Frustrated Lewis Pair Exhibiting High Robustness and Reversible Water Activation: Towards the Metal-Free Hydrogenation of Carbon Dioxide

Cited by 21 publications

References 53 publications

Hydrogen splitting by pyramidalized 13–15 donor–acceptor cryptands: A computational study

Hydrogen splitting by pyramidalized 13–15 donor–acceptor cryptands: A computational study

Reversible Activation of Water by an Air‐ and Moisture‐Stable Frustrated Rhodium Nitrogen Lewis Pair

Ambiphilic Molecules: From Organometallic Curiosity to Metal-Free Catalysts

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