Main Group Redox Catalysis: Reversible P<sup>III</sup>/P<sup>V</sup> Redox Cycling at a Phosphorus Platform

Dunn, Nicole L.; Ha, Minji; Radosevich, Alexander T.

doi:10.1021/ja302963p

Cited by 275 publications

(220 citation statements)

References 40 publications

(26 reference statements)

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“…Chemical proof fort he electrophilicn ature of the phosphenium ligand in this species was derived from its reaction with hydride sourcest ot he anionic phosphine complex [4] À ,w hich can be quenched with acids to yield the neutral metal hydride 5.A lthough the transferred H + /H À pair is released as dihydrogen upon heating or irradiation, an attempt to directly access compound 5 from complex 2 andt he polar H 2 transfer reagent ammonia borane did not result in the expected transfer hydrogenationb ut rather in ac atalytic dehydrogenation of AB. We are currently searching for other phospheniumcomplex-catalysed transfer hydrogenation or dehydrocoupling reactions that complement conventional transition-metalbased and entirely metal-free processes like, for example, (transfer)-hydrogenation and dehydrocoupling promoted by frustrated Lewisp airs, [37] highly electrophilic phosphonium ions [38] or hyper-coordinate phosphorus-based [39] electrophiles. Computational models tudies allowed us to identify two possible reactionp athways in which the AB activation is either accomplished through at ransfer hydrogenation of the Mn=Pd ouble bond or through an entirely ligand-centred mechanism where the substrate transfers aH + /H À pair to the phosphorus atom and one nitrogen atom of the phosphenium ligand.U nexpectedly,t he ligand-centred pathway seems to be somewhat better in accord with the experimental findings but more sophisticated studies are needed to confirmt his mechanistic hypothesis.…”

Section: Resultsmentioning

confidence: 99%

N‐Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic Activity in Ammonia Borane Dehydrogenation

Gediga

Feil

Schlindwein

et al. 2017

Chemistry A European J

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A neutral N-heterocyclic phosphenium complex of manganese was synthesised by a metathesis approach and characterised by IR, NMR, and XRD studies. The short P-Mn distance suggests a substantial metal-ligand double bond character. Reaction with a hydride produced an anionic phosphine complex, which was also characterised by IR and NMR spectroscopy and, after anion exchange, a single-crystal XRD study. Protonation of the anion occurs at the metal to yield a neutral phosphine metal carbonyl hydride, which releases dihydrogen upon irradiation with UV light. These reactions confirm the electrophilic nature of the phosphenium ligand and suggest that the title complex might undergo reactions displaying metal-ligand cooperativity. Surprisingly, reaction with ammonia borane (AB) did not proceed under transfer hydrogenation of the Mn=P double bond but through the catalytic dehydrogenation of AB. The phosphenium complex behaves here as a class II catalyst, which dehydrogenates AB to NH BH that was trapped with cyclohexene. Computational model studies led to the identification of two possible catalytic cycles, which differ in the regioselectivity of the initial AB activation step. In one case, the activation proceeds as cooperative transfer hydrogenation of the Mn=P bond, whereas in the other case a H /H pair is transferred to the phosphorus atom and a nitrogen atom of the phosphenium unit, resulting in a ligand-centred reaction in which the metal fragment acts merely as stabilising substituent. Unexpectedly, this pathway, which constitutes a new reaction mode for phosphenium complexes, seems to be better in accord with experimental findings on the course of the catalysis.

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Section: Resultsmentioning

confidence: 99%

N‐Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic Activity in Ammonia Borane Dehydrogenation

Gediga

Feil

Schlindwein

et al. 2017

Chemistry A European J

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“…The aniline reactions were done at 100°C, whereas the reductions using thiol were performed at 25°C (Table 2, entries 9-12). 2-Methylstyrene was reduced in up to 67% yields under similar conditions using thiophenols as the proton source at 25°C (Table 2, entries 13 and 14), whereas (E)-α-methylstilbene was hydrogenated in high yields using thiophenol or carboxylic acids ( Table 2, entries [15][16][17]. Interestingly, the carboxylic acid C 6 F 5 CO 2 H with Et 3 SiH resulted in complete reduction of internal olefins (E)-α-methylstilbene (Table 2, entry 18) and 1-phenyl-2,2-diphenylethylene in less than 2 h (Table 2, entry 19).…”

Section: Resultsmentioning

confidence: 99%

“…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 addition reactions to polar unsaturates (20), Gabbaï and coworkers (21) have more recently exploited the acceptor capabilities of phosphonium cations, in fluoride sensor strategies.…”

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confidence: 99%

Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis

Pérez

Caputo

Dobrovetsky

et al. 2014

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

140

111

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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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“…[21] Another interesting example is the activation of PH 3 and AsH 3 at as ilylene,w hich was investigated by Driess et al (C, Scheme 1). [24] Recently,t he use of geometrically restrained P III centers in the activation of small molecules has been investigated by Radosevich et al (G) [25,26] and, with adifferent backbone,bythe groups of Aldridge and Goicoechea. [24] Recently,t he use of geometrically restrained P III centers in the activation of small molecules has been investigated by Radosevich et al (G) [25,26] and, with adifferent backbone,bythe groups of Aldridge and Goicoechea.…”

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Metal‐Free Activation of Hydrogen, Carbon Dioxide, and Ammonia by the Open‐Shell Singlet Biradicaloid [P(μ‐NTer)]₂

2016

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The Group 15 open-shell singlet biradicaloid [P(μ-NTer)]2 (Ter=2,6-bis(2,4,6-trimethylphenyl)phenyl) was utilized in the activation of stable small molecules. Fast reactions with H2 , CO2 , and NH3 were observed. Dihydrogen easily added to [P(μ-NTer)]2 , yielding [HP(μ-NTer)]2 under ambient conditions whereas reversible release of molecular hydrogen was observed at slightly elevated temperatures (T>60 °C). As [P(μ-NTer)]2 is a species with phosphorus in the unusual formal oxidation state +II, it is capable of reducing carbon dioxide to afford a zwitterionic compound, [OP(μ-NTer)2 P], and carbon monoxide. The reaction of [P(μ-NTer)]2 with ammonia led to the formation of an azadiphosphiridine after rearrangements of the central P2 N2 heterocycle.

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Main Group Redox Catalysis: Reversible P^III/P^V Redox Cycling at a Phosphorus Platform

Cited by 275 publications

References 40 publications

N‐Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic Activity in Ammonia Borane Dehydrogenation

N‐Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic Activity in Ammonia Borane Dehydrogenation

Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis

Metal‐Free Activation of Hydrogen, Carbon Dioxide, and Ammonia by the Open‐Shell Singlet Biradicaloid [P(μ‐NTer)]₂

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Main Group Redox Catalysis: Reversible PIII/PV Redox Cycling at a Phosphorus Platform

Cited by 275 publications

References 40 publications

N‐Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic Activity in Ammonia Borane Dehydrogenation

N‐Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic Activity in Ammonia Borane Dehydrogenation

Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis

Metal‐Free Activation of Hydrogen, Carbon Dioxide, and Ammonia by the Open‐Shell Singlet Biradicaloid [P(μ‐NTer)]2

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Product

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Main Group Redox Catalysis: Reversible P^III/P^V Redox Cycling at a Phosphorus Platform

Metal‐Free Activation of Hydrogen, Carbon Dioxide, and Ammonia by the Open‐Shell Singlet Biradicaloid [P(μ‐NTer)]₂