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    Home > Further from the activation of metal free dinitrogens: a new chapter in the chemistry of hindered Lewis acid base pairs (FLPs)

    Further from the activation of metal free dinitrogens: a new chapter in the chemistry of hindered Lewis acid base pairs (FLPs)

    • Last Update: 2017-12-18
    • Source: Internet
    • Author: User
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    In the past century, the activation of small molecules such as H 2, CO x, NO x, N 2 are all related to transition metals Indeed, the versatility of D-region metal makes it indispensable in many catalytic cycles Nitrogen is the basic element of life, which exists in many biomolecules Although N 2 is abundant in the atmosphere, because of the stable n ≡ n triple bond, N 2 activation is a huge challenge in both laboratory and industrial scale Nitrogen fixation of biological system is realized by nitrogenase at room temperature, but the reduction of nitrogen to ammonia is still one of the most challenging and important processes in industry, and it needs very harsh conditions It is worth noting that 1-2% of the global energy supply is consumed on the Haber Bosch process every year to achieve the transformation of element nitrogen to fertilizer ammonia Recently, several research groups reported the biomimetic method of N 2 activation, that is, not using natural enzyme to simulate the active site of nitrogenase Although Fe / Mo system has been proved to be able to combine and reduce dinitrogen, other simpler single transition metal catalysts are beginning to dominate the transition metal field In 2006, the reversible activation of hydrogen by nonmetallic compounds was reported, which is a breakthrough research The field of FLP chemistry was born, which indicated the paradigm shift of the main group chemistry Because of the existence of the UN quenched Lewis acid (electrophilic) and Lewis base (nucleophilic) sites, these compounds can represent the front-line orbits of transition metal catalysts, and have the ability to receive and supply electrons at the same time This feature enables FLPs to activate a variety of small molecules, including hydrogen, carbon oxides, nitrogen oxides and other gas molecules, as well as sulfur oxides and π bonds However, the method of metal free activation of N 2 is still unclear Figure 1 Source of FLPs activated small molecules: angelw Chem Int ed in recent years, the possibility of activating N 2 in a metal free manner has been speculated, although the idea emerged as early as 15 years ago Although there have been many reports on the breakthrough of the main group chemistry in recent years, the reduction of metal free N2 is still an obscure idea For small molecule activation, boranes, especially B (C6F5) 3 and its related fluorinated derivatives, are popular in recent years These compounds are widely used in FLP chemistry and Lewis acid catalysis because of their strong Lewis acid and large steric resistance However, it was not until the beginning of 2017 that szymczak and Simonneau discovered the interaction of transition metal N 2 complexes (Fig 2, top) Szymczak uses strong Lewis acid B (C6F5) 3 to activate the weaker N-N bond in fe-n2, which mimics the push-pull hypothesis of nitrogenase activation site (J am Chem SOC 2017, 139, 5952-5956) Simonneau explained this synergy with FLP mechanism (angelw Chem Int ed 2017, 56, 12268-12272) Recently, Stephan and his colleagues published an article called "1,1-hydroboration and abrane addition of diphenyldiazomethane: a potential prelude to flp-n 2 chemistry", which further brought the activation of metal-free N 2 closer to reality (Figure 2, bottom) In Stephan's paper, diphenyldiazomethane can react with B (C6F5) 3 and Hb (C6F5) 2 through the formation of addition products (angel Chem Int ed 2017, DOI: https://doi.org/10.1002/anie.201710337) Figure 2 Source of N-N bond activation by borane Lewis acid: angelw Chem Int ed significant progress in the use of FLPs to activate diazo in 2017 The electron density of N 2 is "pushed" to N 2 part by the electron rich Lewis alkali metal, and the electron density of N 2 is "pulled" by the strong Lewis acid B (C6F5) 3, which can weaken the N-N bond With the increasing attention of the main group chemistry in chemical transformation, researchers also put forward questions about bypassing transition metals Stephan and his colleagues have shown that in the near future, the activation of metal-free N2 is possible, which also provides a new goal for the field of FLPs In the next few years, it is likely that there will be metal free systems that can activate and functionalize N2 This discovery will further consolidate the importance of the main group chemistry in the activation of small molecules Article link: http://onlinelibrary.willey.com/doi/10.1002/anie.201711945/full original author: Rebecca L Melen (Cardiff University) http:// Rebecca L Melen
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