Das erste persistente <i>β</i>‐Silyl‐substituierte Vinyl‐Kation

Siehl, Hans‐Ullrich; Kaufmann, Frank‐Peter; Apeloig, Yitzhak; Braude, V.; Danovich, David; Berndt, A.; Stamatis, Nikolaos

doi:10.1002/ange.19911031139

Cited by 43 publications

(4 citation statements)

References 24 publications

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“…The chemical shifts are reported relative to the residual signals of incompletely deuterated solvent CHD 2 OD (3.31 ppm). The probe temperature was calibrated with a 13 C chemical shift thermometer using neat 2-chlorobutane …”

Section: Methodsmentioning

confidence: 99%

Dynamics of Noncovalent Supramolecular Complexes. NMR Study of the Rotational Barriers in Chiral BINAP Palladium(II) and Platinum(II) Bis(phosphane) Complexes That Resemble the Minimal Subunits of Chiral Polygons and Polyhedra

et al. 1999

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In the reaction between 3-picoline, 2-bromo-5-methylpyridine, 2-methylquinoline, 3-methylisoquinoline, and [M(R-(+)-BINAP)][OTf]2 (M = Pd, Pt; BINAP = 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl), the nature and the distribution of the products were investigated by various physical and spectroscopic methods. The α-substituents on the heteroaryl ring, such as the bromine atom in 2-bromo-5-methylpyridine or the methyl group in 2-methylquinoline, tend to promote the simultaneous formation of mono(heteroaryl)- and bis(heteroaryl)-containing products. The reaction of the most sterically demanding 2-methylquinoline favors the formation of mono(heteroaryl) complexes exclusively within the limits of NMR detection. Reaction of 3-picoline with the chiral Pd(II) and Pt(II) bis(triflates) results in the formation of diastereomeric, square-planar, cationic complexes, due to the hindered rotation about the metal−nitrogen heteroaryl bond. 1H NMR variable-temperature studies of [M(R-(+)-BINAP)(3-picoline)2][OTf]2 were performed. The activation barriers for the rotation of the β-picoline ligands around the M−N linkage axis were determined for [Pd(R-(+)-BINAP)(3-picoline)2][OTf]2 and [Pt(R-(+)-BINAP)(3-picoline)2][OTf]2 by a kinetic line shape analysis of the methyl signals. The Gibbs free energy of activation was found to be 12(±0.5) kcal/mol for the Pd complex 15 and 14(±0.5) kcal/mol for the Pt complex 16. Ab initio calculations (HF/lanl2dz) of model complexes [dpe]Pd(HNCH2)2 2+ and [dpe]Pt(HNCH2)2 2+ (dpe = diphosphinoethylene) provided insights into the observed results. The nitrogen−metal π−σ-interaction is found to be stronger for the Pt complex, resulting in a higher energy barrier for the rotation around the Pt−N bond compared to the rotation around the Pd−N bond. A comparison is made between the covalent and coordinated Pt(II) complexes, and the similarities and differences of their dynamic behavior are discussed.

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Section: Methodsmentioning

confidence: 99%

Dynamics of Noncovalent Supramolecular Complexes. NMR Study of the Rotational Barriers in Chiral BINAP Palladium(II) and Platinum(II) Bis(phosphane) Complexes That Resemble the Minimal Subunits of Chiral Polygons and Polyhedra

et al. 1999

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“…Vinyl cations are well‐established reaction intermediates in many synthetic transformations in organic chemistry 1. Direct spectroscopic evidence for vinyl cations in superacidic media was provided by low temperature NMR studies2–6 and recently significant progress in the synthetic methodology allowed the isolation of salts of stabilized vinyl cation, such as 1 [B(C 6 F 5 ) 4 ], at room temperature7–12 and the experimental molecular structures of two examples were determined by X‐ray diffraction methods (Chart ) 11, 12. These recent advancements are a result of (i) kinetic stabilization by the reaction conditions, that is, weakly coordinating anions and aromatic hydrocarbons as solvents, and (ii) the thermodynamic stabilization by hyperconjugational interaction between the dicoordinated carbon atom C + and the two β‐silyl groups.…”

Section: Introductionmentioning

confidence: 99%

Hyperconjugation in β,β′‐silyl substituted vinyl cations – indications from IR spectroscopy

Klaer

Müller

2010

J of Physical Organic Chem

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Alkyl substituted vinyl cations 1a–c have been synthesized in the form of their [B(C6F5)4]− salts and have been characterized by NMR and IR spectroscopy. The IR absorption bands detected for the νas(CC+) vibrations in vinyl cations are of great diagnostic value, due to their high intensity and relative isolated position in the IR spectra ($\tilde {\nu }$ = 1930–2020 cm−1). DFT calculations of the harmonic force constants at the B3LYP/cc‐pvtz level of theory allowed for an unequivocal assignment of the band after scaling of the theoretical values to account for the anharmonicity of the experimental vibrational potential. A study on the energy of the νas(CC+) of alkyl (1) and aryl substituted vinyl cations (2) revealed a systematic trend, which indicates a decreasing stabilization of the vinyl cations by β‐SiC hyperconjugation when the electron donating ability of the substituent R2 next to the positively charged carbon atom is increased. Copyright © 2010 John Wiley & Sons, Ltd.

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“…Die Reaktion von 1 mit äquim olaren Mengen LiBu' führt in unpolaren Lösungsmitteln (hier: /7-Pentan) und bei -7 8 °C zunächst zur Addition des Lithiumorganyls an die vinylische D oppelbin dung (Nutzung des Si-/?-Effekts [14]; Bildung von a-Lithioaddukt A). In einem Folgeschritt spaltet sich bei Tem peraturen zwischen -1 5 und 0 °C aus A -möglicherweise über eine Zwischenverbin dung B (Silaethen/LiCl-Addukt) -intram olekular LiCl ab; dabei entsteht Silaethen 2 als reaktives Interm ediat [15].…”

Section: Ergebnisseunclassified

“…' Z-l,l-D ichlor-2-neopentyl-2,3-diphenyl-l -silacyclobutan (Z-14) 'H -N M R : ö = 0,66 (s, 9 H , C (C H 3) Dichlor-l-neopentyl-1 -phenyl-2-sila-l ,2,3,5-tetrahydronaphthalin (15) exo-E/Z-19: MS (CI): m/e M+ = 351 (M + + l, 13), 317 (22), 295 (40), 259 (16), 159 (19), 145 (51), 117 (14); (Synthese aus Quadricyclan).…”

Section: E -L 1 -Dichlor-2-neopentyl-23-diphenyl-l -Silacyclobutan mentioning

confidence: 99%

Silaheterocyclen, XXVII. Substituenteneffekte zur Steuerung des Cycloadditionsverhaltens von Silaethenen [1] / Silaheterocycles, XXVII. Controlling the Cycloaddition Behavior of Silenes by Substituent Effects [1]

1994

Zeitschrift Für Naturforschung B

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The silene Cl2Si=C(Ph)CH2But (2) is formed by the reaction of 1,1,1-trichloro-2-phenyll- silaprop-2-ene (1) with LiBut in n-pentane in the temperature range from -15 to 0 °C. The reaction initially leads to the corresponding α-lithio adduct A (addition of LiBut to the vinyl group of 1); subsequent LiCl elimination yields 2 as an intermediate. 2 can be trapped by Me3SiOMe (3) and dienes which add across the Si=C bond. In the absence of trapping agents but in the presence of the Lewis base NEt3 the mixture 1/LiBut reacts to give the disilacyclobutane 4. Due to its electronic and steric properties, Cl2Si=C(Ph)CH2But (2) and butadienes yield mainly the Diels-Alder adducts (5, 7, 9) while with styrene and 1,3-cyclohexadiene the [2+2] and [4+2] products are formed in competition. With 2-norbornene, 2,5-norbornadiene and quadricyclan the [2+2] and [2+2+2] products are formed selectively but only in low yields. In all reactions except with quadricyclan an ene-reaction competes with the cycloaddition leading to ene-compounds as by-products

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Das erste persistente β‐Silyl‐substituierte Vinyl‐Kation

Abstract: raturen oberhalb + 50°C zwei Signale fur Methylenkohlenstoffatome, bei tiefen Temperaturen ( 5 -25 "C) vier scharfe Signale. Demnach liegen von 15 b zwei Konformere nebena . X = H ; b . X = B r 14 15

Cited by 43 publications

References 24 publications

Dynamics of Noncovalent Supramolecular Complexes. NMR Study of the Rotational Barriers in Chiral BINAP Palladium(II) and Platinum(II) Bis(phosphane) Complexes That Resemble the Minimal Subunits of Chiral Polygons and Polyhedra

Dynamics of Noncovalent Supramolecular Complexes. NMR Study of the Rotational Barriers in Chiral BINAP Palladium(II) and Platinum(II) Bis(phosphane) Complexes That Resemble the Minimal Subunits of Chiral Polygons and Polyhedra

Hyperconjugation in β,β′‐silyl substituted vinyl cations – indications from IR spectroscopy

Silaheterocyclen, XXVII. Substituenteneffekte zur Steuerung des Cycloadditionsverhaltens von Silaethenen [1] / Silaheterocycles, XXVII. Controlling the Cycloaddition Behavior of Silenes by Substituent Effects [1]

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