Metal-Free Transfer Hydrogenation Catalysis by B(C6F5)3

Farrell, Jeffrey M.; Heiden, Zachariah M.; Stephan, Douglas W.

doi:10.1021/om2005832

Cited by 111 publications

(92 citation statements)

References 47 publications

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“…[30] It is well established that B(C 6 F 5 ) 3 is able to abstract hydride from amines in the a-position to nitrogen. [31] Stephan et al [32] observed that secondary amines undergo racemization upon treatment with the Lewis acid B(C 6 F 5 ) 3 , and further developed this into a B(C 6 F 5 ) 3 -catalyzed transfer hydrogenation of imines, enamines, quinolines, and aziridines using diisopropylamine as the hydrogen source (Scheme 6).…”

Section: Hydrogen Splitting and Metal-free Hydrogenationmentioning

confidence: 99%

Frustrated Lewis Pair Chemistry: Development and Perspectives

2015

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Frustrated Lewis pairs (FLPs) are combinations of Lewis acids and Lewis bases in solution that are deterred from strong adduct formation by steric and/or electronic factors. This opens pathways to novel cooperative reactions with added substrates. Small-molecule binding and activation by FLPs has led to the discovery of a variety of new reactions through unprecedented pathways. Hydrogen activation and subsequent manipulation in metal-free catalytic hydrogenations is a frequently observed feature of many FLPs. The current state of this young but rapidly expanding field is outlined in this Review and the future directions for its broadening sphere of impact are considered.

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Section: Hydrogen Splitting and Metal-free Hydrogenationmentioning

confidence: 99%

Frustrated Lewis Pair Chemistry: Development and Perspectives

2015

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“…Transfer hydrogenations of ketones, aldehydes, and imines can be achieved by the classic Meerwein-Ponndorf-Verley protocol, catalyzed by a variety of transition metal complexes and more recently by FLPs (38). In contrast, transfer hydrogenation of olefins has received much less attention.…”

Section: N (H)sir 3 ]mentioning

confidence: 99%

Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis

Pérez

Caputo

Dobrovetsky

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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A major advance in main-group chemistry in recent years has been the emergence of the reactivity of main-group species that mimics that of transition metal complexes. In this report, the Lewis acidic phosphonium salt [(C 6 F 5 ) 3 PF][B(C 6 F 5 ) 4 ] 1 is shown to catalyze the dehydrocoupling of silanes with amines, thiols, phenols, and carboxylic acids to form the Si-E bond (E = N, S, O) with the liberation of H 2 (21 examples). This catalysis, when performed in the presence of a series of olefins, yields the concurrent formation of the products of dehydrocoupling and transfer hydrogenation of the olefin (30 examples). This reactivity provides a strategy for metalfree catalysis of olefin hydrogenations. The mechanisms for both catalytic reactions are proposed and supported by experiment and density functional theory calculations. fluorophosphonium A wide range of commodity chemicals, petrochemicals, pharmaceuticals, materials, and foods depend on industrial-scale hydrogenation reactions. Catalysts for this process are based on both heterogeneous transition metals materials and homogeneous transition metal complexes. Indeed, it was the discovery of Sabatier (1) in the early 20th century that revealed the utility of amorphous Ni and other metals in hydrogenation processes. Following the dawn of organometallic chemistry in the 1960s, homogeneous catalysts were developed principally based on precious metals (2-4). Although subsequent modifications and optimizations have led to numerous highly selective and efficient catalyst technologies, concerns over cost, natural abundance, and toxicity have prompted efforts to uncover catalysts based on "earth-abundant" elements. The principal targets in these efforts have been the first-row transition metals. Indeed, the groups of Chirik (5, 6), Morris (7), Beller (8), and others (9) have developed remarkably active and selective catalysts based on Fe.Strategies to develop reduction methods using organic or main-group-based reagents have also been explored. For example, use of Hantzsch esters (10), Birch reduction of arenes (11), or the use of B or Al hydrides are effective, albeit stoichiometric reductions. More recently, the advent of "frustrated Lewis pairs" (FLPs) have led to the discovery that combinations of sterically encumbered donors and acceptors act as catalysts for the reductions of imines, enamines, silylenol ethers, olefins, and alkynes (12).To uncover hydrogenation strategies using earth-abundant elements, we have focused our efforts on Lewis acidic phosphorus species. Although Gudat (13), Burford and coworker (14), Yoshifuji (15), and Bertrand and coworker (16), among others, have reported phosphenium cations that demonstrate Lewis acidity, Radosevich and coworkers (17) have exploited the reaction of the unique planar P(III) species with ammoniaborane to give a P(V)H 2 derivative that effects the subsequent reduction of diazobenzene. Although the acidity of P(V) has been exploited previously in ylide reagents (18), Diels-Alder reactions catalysis (19), and add...

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“…We thus accomplished the transfer hydrogenation of imines (Scheme 1, top). [10,13] Theapplication of this approach to alkenes is aworthwhile goal as it would allow for the transfer of dihydrogen from one unsaturated hydrocarbon to another unsaturated hydrocarbon in aprocess that is catalyzed by amain-group Lewis acid (Scheme 1, bottom). [14,15] However,t he involvement of carbenium ions at different stages of this process is likely to provoke cationic oligomerization of both reaction partners.It must be mentioned that Stephan and co-workers recently reported one example of aB (C 6 F 5 ) 3 -catalyzed alkene hydrogenation that required assistance by Et 2 Oa saL ewis basic component.…”

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confidence: 99%

B(C₆F₅)₃‐Catalyzed Transfer of Dihydrogen from One Unsaturated Hydrocarbon to Another

Chatterjee

Grimme

et al. 2015

Angew Chem Int Ed

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A transition-metal-free transfer hydrogenation of 1,1-disubstituted alkenes with cyclohexa-1,4-dienes as the formal source of dihydrogen is reported. The process is initiated by B(C6 F5 )3 -mediated hydride abstraction from the dihydrogen surrogate, forming a Brønsted acidic Wheland complex and [HB(C6 F5 )3 ](-) . A sequence of proton and hydride transfers onto the alkene substrate then yields the alkane. Although several carbenium ion intermediates are involved, competing reaction channels, such as dihydrogen release and cationic dimerization of reactants, are largely suppressed by the use of a cyclohexa-1,4-diene with methyl groups at the C1 and C5 as well as at the C3 position, the site of hydride abstraction. The alkene concentration is another crucial factor. The various reaction pathways were computationally analyzed, leading to a mechanistic picture that is in full agreement with the experimental observations.

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Metal-Free Transfer Hydrogenation Catalysis by B(C₆F₅)₃

Cited by 111 publications

References 47 publications

Frustrated Lewis Pair Chemistry: Development and Perspectives

Frustrated Lewis Pair Chemistry: Development and Perspectives

Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis

B(C₆F₅)₃‐Catalyzed Transfer of Dihydrogen from One Unsaturated Hydrocarbon to Another

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Metal-Free Transfer Hydrogenation Catalysis by B(C6F5)3

Cited by 111 publications

References 47 publications

Frustrated Lewis Pair Chemistry: Development and Perspectives

Frustrated Lewis Pair Chemistry: Development and Perspectives

Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis

B(C6F5)3‐Catalyzed Transfer of Dihydrogen from One Unsaturated Hydrocarbon to Another

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Product

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Metal-Free Transfer Hydrogenation Catalysis by B(C₆F₅)₃

B(C₆F₅)₃‐Catalyzed Transfer of Dihydrogen from One Unsaturated Hydrocarbon to Another