Methyl cation affinity (MCA) values for phosphanes

Lindner, Christoph; Maryasin, Boris; Richter, Frank; Zipse, Hendrik

doi:10.1002/poc.1726

Cited by 23 publications

(10 citation statements)

References 33 publications

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“…Analysis of the results for unbranched trialkylphosphanes indicates that longer alkyl chains increase the MCA values in a systematic manner. This was also found for trialkylamines and reflects inductive electron donation through alkyl substituents with variable length [ 13 ]. The results obtained for dimethylalkylphosphanes of general structure Me 2 P(CH 2 ) n H with n = 1–8 lead to a general expression for the chain-length dependence of the MCA values that can again be derived as given in equation 4 ( Scheme 4 ).…”

Section: Resultsmentioning

confidence: 72%

Cation affinity numbers of Lewis bases

Lindner

Tandon²,

Maryasin³

et al. 2012

Beilstein J. Org. Chem.

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SummaryUsing selected theoretical methods the affinity of a large range of Lewis bases towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles.

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Section: Resultsmentioning

confidence: 72%

Cation affinity numbers of Lewis bases

Lindner

Tandon²,

Maryasin³

et al. 2012

Beilstein J. Org. Chem.

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“…The donor potential of phosphines was experimentally and theoretically determined by their carbocation affinity by Kempf and Mayr 27 and Zipse. 28 These methods support a linear dependence of nucleophilicity and pK a for the conjugate acids. Accordingly, the pK a is an ideal and straightforward accessible parameter for the classication of Lewis bases in FLP-mediated H 2 -activation.…”

Section: Electronic and Structural Features Of Ortho-substituted Tria...mentioning

confidence: 72%

Electronic effects of triarylphosphines in metal-free hydrogen activation: a kinetic and computational study

et al. 2013

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The frustrated Lewis pair-mediated reversible hydrogen activation is studied as a function of the electrondonor quality of a series of phosphines. The increasing acidity of the generated phosphonium species leads to a stepwise lowering of the temperature for the highly reversible H 2 -activation and permits concrete classification for the first time. The influence of the acid strength on the metal-free hydrogenation of selected olefins is investigated by kinetic experiments and quantum chemical calculations. Detailed information for the rate-determining steps fully support our mechanistic model of a protonation step prior to hydride transfer. The rate of hydrogenation is strongly dependent on the electronic nature of the phosphine and of the acidity of the corresponding phosphonium cation. A careful balance of these two factors provides highly efficient metal-free hydrogenation catalysts. The provided findings are used to revise the reactivity of Lewis bases in the hydrogenation of imines, one of the most recognized applications of FLPs.

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“…2,3,9,10 In an attempt to quantitatively account for the Lewis basicity of available phosphines, computational methods have been used to calculate the reaction enthalpy for the methyl detachment reaction. 11 Methyl Cation Affinity is chosen over pK a or analogous transition metal indices for ligand activity as a measure of the Lewis basicity of phosphines due to the closer correlation between the methyl cation and isoelectronic boron centre. Tris-tert-butylphosphine (P( t Bu) 3 ) has been used extensively in FLP chemistry to induce small molecule activation, [12][13][14] heterolytically cleave H 2 .…”

Section: Synthesis Of Novel Flpsmentioning

confidence: 99%

Small molecule activation by frustrated Lewis pairs

et al. 2013

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A series of frustrated Lewis pairs (FLPs) based on the Lewis acids tris(perchloroaryl)borane (BAr(Cl)), and tris(2,2',2''-perfluorobiphenyl)borane (PBB) and trialkylphosphines were prepared; their ability to effect the heterolytic cleavage of dihydrogen, insert carbon dioxide into the borohydride, and reduce the resulting formatoborate to methanol were studied. Additionally, the insertion of CO(2) into a B-OH bond is explored with the ultimate aim of developing a homogeneous, catalytic preparation of carbonates. The compound [PBB-OH][H-P((t)Bu)(3)] was characterised by single crystal X-ray crystallography.

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Methyl cation affinity (MCA) values for phosphanes

Cited by 23 publications

References 33 publications

Cation affinity numbers of Lewis bases

Cation affinity numbers of Lewis bases

Electronic effects of triarylphosphines in metal-free hydrogen activation: a kinetic and computational study

Small molecule activation by frustrated Lewis pairs

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