The Highly Lewis Acidic Dicationic Phosphonium Salt: [(SIMes)PFPh2][B(C6F5)4]2

Holthausen, Michael H.; Mehta, Meera; Stephan, Douglas W.

doi:10.1002/anie.201403693

Cited by 142 publications

(101 citation statements)

References 45 publications

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“…In contrast to a related difluorophosphorane, 23 which requires a very strong fluoride abstracting reagent such as Et 3 Si[B(C 6 F 5 ) 4 ]·2(C 7 H 8 ), the reaction of 15a,b[OTf ] with Me 3 SiOTf in CH 2 Cl 2 quantitatively gives the fluorophosphonium salts 16a,b [OTf ]. Analytically pure compounds are obtained after the addition of n-hexane (isolated yield >70%).…”

Section: Resultsmentioning

confidence: 99%

Cationic 5-phosphonio-substituted N-heterocyclic carbenes

et al. 2016

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2-Phosphanyl-substituted imidazolium salts 2-PR2(4,5-Cl-Im)[OTf] (9a,b[OTf]) (4,5-Cl-Im = 4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolium) (a: R = Cy, b: R = Ph) are prepared from the reaction of R2PCl (R = Cy, Ph) with NHC 8 (4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolin-2-ylidene) in the presence of Me3SiOTf. 5-Phospanyl-substituted imidazolium salts 5-PR2(2,4-Cl-Im)[OTf] (10a,b[OTf]) are obtained in quantitative yield when a slight excess of the NHC 8 is used. 5-Phosphonio-substituted imidazolium salts 5-PR2Me(2,4-Cl-Im)[OTf]2 (14a,b[OTf]2) and 5-PR2F(2,4-Cl-Im)[OTf]2 (16a,b[OTf]2) result from methylation reaction or oxidation of 10a,b[OTf] with XeF2 and subsequent fluoride abstraction. According to our quantum chemical studies the Cl1 atom at the 2-position at the imidazolium ring of dication 14b(2+) carries a slightly positive charge and is therefore accessible for nucleophilic attack. Accordingly, the reaction of 14a,b[OTf]2 and 16a,b[OTf]2 with R3P (R = Cy, Ph) affords cationic 5-phosphonio-substituted NHCs 5-PR2Me(4-Cl-NHC)[OTf] (17a,b[OTf]) and 5-PR2F(4-Cl-NHC)[OTf] (18a,b[OTf]) via a SN2(Cl)-type reaction. A series of transition metal complexes such as [AuCl(5-PPh2Me(4-Cl-NHC))][OTf] (19[OTf]), [CuBr(5-PPh2Me(4-Cl-NHC))][OTf] (20[OTf]), [AuCl(5-PPh2F(4-Cl-NHC))[OTf] (21[OTf]) and [RhCl(cod)(5-PPh2Me(4-Cl-NHC))][OTf] (23[OTf]) are prepared to prove the coordination abilities of carbenes 17b[OTf] and 18b[OTf]. The isolation of a rare example of a tricationic bis-carbene silver complex [Ag(5-PPh2Me(4-Cl-NHC))2][OTf]3 (22[OTf]3) is achieved by reacting 14b[OTf] with Cy3P in the presence of AgOTf. NHC 17b[OTf] represents a very effective dehydrocoupling reagent for secondary (R2PH, R = Ph, Cy, (i)Bu) and primary (RPH2, R = Ph, Cy) phosphanes to give diphosphanes of type R4P2 (R = Ph, Cy, (i)Bu) and oligophosphanes R4P4, R5P5 (R = Ph, Cy), respectively. Methylation of 17b(+) and subsequent deprotonation reaction with LDA affords the cationic NHO (N-heterocyclic olefin) 35(+) of which the gold complex 36(+) is readily accessible via the reaction with AuCl(tht).

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Section: Resultsmentioning

confidence: 99%

Cationic 5-phosphonio-substituted N-heterocyclic carbenes

et al. 2016

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“…[111,196] Efforts to broaden the structural variety of EPCs has led to the synthesis of the formally dicationic [(SIMes)PFPh 2 ] [B(C 6 F 5 ) 4 ] 2 (492). [197] 4 ] (491) and subsequent fluoride abstraction. The resulting species 492 (Scheme 138) is remarkably Lewis acidic in both stoichiometric reactions.…”

Section: Electrophilic Phosphorus Cations (Epcs)mentioning

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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“…44 The first step in this mechanism is believed to be olefin activation, which generates a transient carbocation and affects electrophilic attack on the aryl moiety with concurrent proton transfer to the olefin. 45 EPCs were also shown to mediate ketone deoxygenation in the presence of excess silane. This reactivity demonstrates that the dication is more fluorophilic than [(C 6 F 5 ) 3 PF] + , inferring that the presence of the dicationic charge plays a greater role in generating Lewis acidity than electronwithdrawing substituents.…”

Section: Pf][b(c 6 F 5 ) 4 ] In the Presence Of [Et 3 Si][b(c 6 F 5 )mentioning

confidence: 99%

Phosphorus Lewis acids: emerging reactivity and applications in catalysis

2016

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Part of the renaissance in main group chemistry has been a result of the focus on reactivity. This has led to the development of applications in stoichiometric reactivity and catalysis. In this tutorial review, we focus attention on the role of phosphorus-based Lewis acids in such advances. While early literature recognizes the role of P(iii) and P(v) electrophiles in coordination chemistry, it has generally been more recent studies that have focused on applications of this Lewis acidity. Applications of these novel P-based Lewis acids in stoichiometric reactivity, Lewis acid catalysis and frustrated Lewis pair (FLP) reactivity are reviewed. These advances demonstrate that P-based Lewis acids are a powerful tool for further developments in metal-free catalysis.

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The Highly Lewis Acidic Dicationic Phosphonium Salt: [(SIMes)PFPh₂][B(C₆F₅)₄]₂

Abstract: The dicationic imidazolium-phosphonium salt [(SIMes)PFPh2][B(C6F5)4]2 has been prepared and shown to exhibit remarkable Lewis acidity in stoichiometric reactions and acting as an effective Lewis acid catalyst for the hydrodefluorination of fluoroalkanes and the hydrosilylation of olefins.

Cited by 142 publications

References 45 publications

Cationic 5-phosphonio-substituted N-heterocyclic carbenes

Cationic 5-phosphonio-substituted N-heterocyclic carbenes

Frustrated Lewis Pair Chemistry: Development and Perspectives

Phosphorus Lewis acids: emerging reactivity and applications in catalysis

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