One-pot, room-temperature conversion of dinitrogen to ammonium chloride at a main-group element

Légaré, Marc‐André; Bélanger‐Chabot, Guillaume; Rang, Maximilian; Dewhurst, Rian D.; Krummenacher, Ivo; Bertermann, Rüdiger; Braunschweig, Holger

doi:10.1038/s41557-020-0520-6

Cited by 105 publications

(76 citation statements)

References 41 publications

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“…As such, B is considerably more stable than A, making the regeneration of the latter an energetically uphill process. Thus, this new report 13 provides hope for the future but also demonstrates the formidable challenge remaining to make the process practical, feasible and economical-namely the regeneration of a species that will activate dinitrogen, presumably a high-energy species such as A (Fig. 2).…”

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confidence: 88%

“…Indeed, while we were able to demonstrate the unprecedented synthesis of ammonium using a p-block species, along with a full elucidation and structural authentication of the key intermediates in the process (Fig. 2), a strong acid (HCl) is required in order to release the product from the boron reagent 13 Fig. 2) in the demonstrated production of ammonium, while conceptually an adduct of NH 3 with the presumed N 2 -activating species A, is essentially a conventional aminoborane.…”

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confidence: 97%

“…Details of the isolated compounds can be found in refs. 11,13 . Figure adapted with permission from ref.…”

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confidence: 99%

“…An alternative, but potentially complementary, strategy is to devise and test potential additives or physical methods that can assist with key steps of the reaction but will not quench the highly reactive activating species, such as photolysis, steric shielding, solubility differences, etc. An interesting example of this can be seen in our one-pot synthesis of ammonium chloride from N 2 13 , wherein the strong reductant (potassium graphite) and the proton source (boric acid) coexist in the reaction mixture and take part in the reaction, but do not interact with each other due to their low solubility. In time, through catalyst design and the employment of additives and/or physical stimulus, there is hope that the challenge of combining high activating power with catalytic turnover can be met.…”

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Towards the catalytic activation of inert small molecules by main-group ambiphiles

2020

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The activation of very inert small molecules generally requires highly reactive activating species, but the high energy of these species makes their regeneration, and thus also catalytic turnover of the reaction, difficult to achieve. Here, the authors highlight the formidable challenge of overcoming the tradeoff between activating power and catalytic turnover in the context of main-group ambiphiles. There is intense current interest in the possibility of using main-group elements in the place of transition metals (TMs) in molecular catalysis 1,2 , due mainly to the cost of the metals themselves and increasing concerns about the health and environmental impact of the residual metal retained in the products. Along these lines, main-group ambiphiles, as embodied by dual-site ambiphiles such as frustrated Lewis pairs (FLPs) 3 and single-site ambiphiles such as singlet carbenes (CR 2) 4-6 , constrained phosphines 7 , dicoordinate borylenes (LBR, L = Lewis donor) 8,9 and dicoordinate group 14 cations 10 have begun to emerge as powerful TM-free reagents for the activation of inert small molecules of catalytic interest (Fig. 1). Mimicking TMs, these ambiphilic species combine filled and vacant orbitals to break bonds of substrates by synergic donation and acceptance of electron density. However, merely binding and breaking bonds of a substrate has limited utility; the ability to form and liberate a product, while also regenerating the active reagent and thus making the process catalytic (or at least recyclable), is the true goal of smallmolecule activation. It is here where very inert small molecules (e.g., N 2 , alkanes, etc.) present a major challenge to catalysis: the more inert the substrate, the more reactive the activating agent needs to be, and regenerating this high-energy species for catalytic turnover can become difficult in a thermodynamic (if not also kinetic) sense. Our recent discovery of the binding and reduction of N 2 at boron 11 has provided inspiration for the use of main-group species to activate the most inert of substrates. Our work in this area not only highlights the potential of main-group single-site ambiphiles to perform very challenging transformations that are usually the preserve of transition metal chemistry, but has also

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confidence: 88%

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confidence: 97%

“…Details of the isolated compounds can be found in refs. 11,13 . Figure adapted with permission from ref.…”

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confidence: 99%

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confidence: 99%

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Towards the catalytic activation of inert small molecules by main-group ambiphiles

2020

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“…31 With boron-centred lled and vacant orbitals, this species was the rst crystalline borylene with an electronic structure similar to that of a transition metal, and was able to effect metallomimetic reactivity in the binding of CO and scission of dihydrogen at ambient temperature. 32 In another advance, in 2018 we reported the capture of dinitrogen by a eeting singly base-stabilised borylene, 33,34,42,43 revealing the powerful ability of these emerging species to activate highly inert bonds (Scheme 1). 37 Ligand exchange is a hallmark of transition metal chemistry, allowing reversible bond activations that are crucial steps in a multitude of catalytic processes, and is an emerging property of low-valent main group species.…”

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Phosphinoborylenes as stable sources of fleeting borylenes

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Low Valent Main Group Compounds in Small Molecule Activation

Weetman

2021

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Since the discovery that main group elements can mimic transition metals, efforts have focussed on harnessing main group elements' abilities to break strong bonds to enable new sustainable methodologies. In this regard, use of small molecules, such as those found in greenhouse gases, is a prime target for incorporation into catalytic cycles to produce value‐added products. Initial challenges in main group chemistry focussed on the ability to isolate these highly reactive low‐oxidation state species, whilst also maintaining the reactive sites. An array of low valent compounds have been successfully isolated (i.e., multiple bonds, tetrylenes, anions, and cations), through careful ligand design, and have challenged traditional bonding models and preconceptions of the main group elements. Current advances have highlighted how reactive these low‐valent sites are with the ability to activate strong bonds, such as those found in small molecules (e.g., H 2 , CO, CO 2 , etc.). This represents the first step in a redox‐based catalytic cycle, as the low‐valent main group center undergoes oxidative addition reactions. Current challenges remain in reductive elimination, and thus functionalization of the small molecule, but examples of low‐valent main group elements in catalysis are starting to emerge and represent a bright future for main group chemistry. This article highlights the achievements of low valent main group elements, with a focus on group 2, 13, and 14 elements, in small molecule activation as well as the fundamental concepts that have aided the development of this rapidly advancing field.

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One-pot, room-temperature conversion of dinitrogen to ammonium chloride at a main-group element

Cited by 105 publications

References 41 publications

Towards the catalytic activation of inert small molecules by main-group ambiphiles

Towards the catalytic activation of inert small molecules by main-group ambiphiles

Phosphinoborylenes as stable sources of fleeting borylenes

Low Valent Main Group Compounds in Small Molecule Activation

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