Trigonal Planar Phosphorus Cations

and, Olivier Guerret; Bertrand, Guy

doi:10.1021/ar970061a

Cited by 61 publications

(42 citation statements)

References 57 publications

(77 reference statements)

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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%

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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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Section: Resultsmentioning

confidence: 99%

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.

140

111

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“…Clearly, derivative 5 is the desired cation, featuring two σ 3 -phosphorus centers. The 31 P NMR chemical shifts are in the range for a bis(diisopropylamino)(methylene)phosphonium salt [10] and an (alkyl)(amino)(phenyloxy)phosphane; therefore, as predicted by the calculations, this ''1σ 3 ,3σ 3 -diphosphaallylic cation'' features a localized double bond involving the diamino-substituted phosphorus atom and a single bond. In other words, the molecule is probably highly unsymmetrical, the phenyloxy-substituted phosphorus atom remains pyramidal.…”

Section: Resultsmentioning

confidence: 68%

Synthesis of a Persistent 1σ³,3σ³‐Diphosphaallyl Cation Featuring a Localized Phosphorus−Carbon Double Bond

2004

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Abstracttert‐Butyl thiol, 2,6‐dimethylthiophenol, 2,6‐dimethylphenol, and 2,6‐bis(tert‐butyl)‐4‐methylphenol cleanly add to the 1σ4,3σ2‐diphosphacumulene 1 to afford the corresponding C‐phosphanyl phosphorus ylides 2a−d. Treatment of 2a with gallium trichloride quantitatively leads to the C‐phosphonio phosphaalkene 3, resulting from the1,3‐migration of the sulfido group. Under the same experimental conditions, cleavage of the arylthio and aryloxy groups of 2b and 2c leading to the C‐phosphonio phosphaalkene 4 is observed. In the case of the sterically most crowded derivative, 2d, abstraction of the chloride ion affords the 1σ3,3σ3‐diphosphaallyl cation 5, which is stable for several weeks in dichloromethane at −20 °C, but decomposes after a few minutes at above 0 °C. Compound 5 reacts at low temperatures with an excess of acetonitrile or benzaldehyde to afford quantitatively and regioselectively the corresponding five‐membered heterocycles 6 and 7. The NMR spectroscopy data and reactivity suggest that 5 features a localized double bond with a planar diamino‐substituted phosphorus center, and a single bond with a pyramidalized (amino)(aryloxy)phosphanyl group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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“…The 31 P NMR chemical shift of I Rh (d +100.8 ppm) is deshielded by 130 ppm compared to that of the free carbene I, and now appears in the region typically associated with methylene phosphonium salts (trigonal planar phosphorus cations) [40]. Moreover, the 13 C NMR chemical shift for the carbene center (d 120.6 ppm, 1 J C-P ¼ 2 Hz, 1 J C-Rh ¼ 59 Hz) is shielded compared to that of the free carbene (d 146.1 ppm, 1 J C-P ¼ 271 Hz).…”

Section: Ligand Properties Of Non-nhcsmentioning

confidence: 97%