Cooperative THF Ring‐Opening by B(C6F5)3 and a Tellurium Diimide Dimer

Chivers, Tristram; Schatte, Gabriele

doi:10.1002/ejic.200300344

Cited by 26 publications

(18 citation statements)

References 30 publications

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“…[ 22 ] Strong Brønsted acids can initiate polymerization of THF,[ 19b , c ] as can strong Lewis acids, including 1 a . [ 23 ] Nevertheless, during the course of our studies no evidence for borane or proton-catalyzed polymerization of THF was detected for solutions of 1 a – d under H 2 , even after prolonged heating. [ 24 ] Nor, during our subsequent investigations into catalytic hydrogenation, was any FLP-mediated ring-opening of the solvent observed, even in the presence of relatively basic imines.…”

mentioning

confidence: 84%

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

2014

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In recent years ‘frustrated Lewis pairs’ (FLPs) have been shown to be effective metal-free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional-group tolerance restricts the range of solvents in which FLP-mediated reactions can be performed, with all FLP-mediated hydrogenations reported to date carried out in non-donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C6Cl5)x(C6F5)3−x (x=0–3) are capable of heterolytic H2 activation in the strong-donor solvent THF, in the absence of any additional Lewis base. This allows metal-free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal-free catalytic hydrogenation of furan heterocycles. The air-stability of the most effective borane, B(C6Cl5)(C6F5)2, makes this a practically simple reaction method.

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confidence: 84%

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

2014

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“…Clearly H 2 activation in this manner generates a substantially acidic proton (the p K a of protonated THF has been measured as −2.05 in aqueous H 2 SO 4 ) 22. Strong Brønsted acids can initiate polymerization of THF,19b,c as can strong Lewis acids, including 1 a 23. Nevertheless, during the course of our studies no evidence for borane or proton‐catalyzed polymerization of THF was detected for solutions of 1 a – d under H 2 , even after prolonged heating 24.…”

Section: Methodsmentioning

confidence: 99%

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

2014

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In recent years frustrated Lewis pairs (FLPs) have been shown to be effective metal-free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional-group tolerance restricts the range of solvents in which FLP-mediated reactions can be performed, with all FLP-mediated hydrogenations reported to date carried out in non-donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C 6 Cl 5 ) x (C 6 F 5 ) 3Àx (x = 0-3) are capable of heterolytic H 2 activation in the strong-donor solvent THF, in the absence of any additional Lewis base. This allows metal-free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal-free catalytic hydrogenation of furan heterocycles. The air-stability of the most effective borane, B(C 6 Cl 5 )(C 6 F 5 ) 2 , makes this a practically simple reaction method.

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“…[90] Related combinations of Lewis acids and Lewis bases exhibit similar THF ring-opening chemistry. These include systems involving Lewis acidic transition metals, such as U, [91] Sm, [92] Ti, [93] and Zr [90,94] and main-group Lewis acids including carborane, [95] alane, [96] tellurium species, [97] and boranes [98] in combination with either nitrogen-or phosphorus-based Lewis bases (Scheme 53). The most pertinent of these to the present discussion is the zwitterionic species R 2 PH(CH 2 ) 4 OB(C 6 F 5 ) 3 (R = tBu, C 6 H 2 Me 3 ) derived from the treatment of (THF)B-(C 6 F 5 ) 3 with sterically encumbered phosphines.…”

Section: Ring Opening Of Thfmentioning

confidence: 99%

Frustrated Lewis Pairs: Metal‐free Hydrogen Activation and More

2009

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Sterically encumbered Lewis acid and Lewis base combinations do not undergo the ubiquitous neutralization reaction to form "classical" Lewis acid/Lewis base adducts. Rather, both the unquenched Lewis acidity and basicity of such sterically "frustrated Lewis pairs (FLPs)" is available to carry out unusual reactions. Typical examples of frustrated Lewis pairs are inter- or intramolecular combinations of bulky phosphines or amines with strongly electrophilic RB(C(6)F(5))(2) components. Many examples of such frustrated Lewis pairs are able to cleave dihydrogen heterolytically. The resulting H(+)/H(-) pairs (stabilized for example, in the form of the respective phosphonium cation/hydridoborate anion salts) serve as active metal-free catalysts for the hydrogenation of, for example, bulky imines, enamines, or enol ethers. Frustrated Lewis pairs also react with alkenes, aldehydes, and a variety of other small molecules, including carbon dioxide, in cooperative three-component reactions, offering new strategies for synthetic chemistry.

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Cooperative THF Ring‐Opening by B(C₆F₅)₃ and a Tellurium Diimide Dimer

Cited by 26 publications

References 30 publications

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

Frustrated Lewis Pairs: Metal‐free Hydrogen Activation and More

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