Persistent Silylium Ions Stabilized by Polyagostic SiH⋅⋅⋅Si Interactions

Khalimon, Andrey Y.; Lin, Zi Hua; Simionescu, Razvan; Vyboishchikov, Sergei F.; Nikonov, Georgii I.

doi:10.1002/ange.200604258

Cited by 17 publications

(6 citation statements)

References 71 publications

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“…This is similar to coordinated (Me 3 Si)(B(C 6 F 5 ) 4 ) (MAS NMR: δ =84.8 ppm)32 or the with respect to Si half ionized [Me 3 Si‐H‐SiMe 3 ][HCB 11 Cl 11 ] ( δ =85.4 and 82.2 ppm) 28. 33, 34 All other spectroscopic data of 1 are as expected and not discussed herein, but are included in the Supporting Information.…”

Section: Comparison Of the Bonding Situation Between (Me3si)(etcb11fsupporting

confidence: 56%

A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me₃Si‐F‐Al(OR^F)₃

Rohde

Müller

Himmel

et al. 2014

Chemistry A European J

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Upon reaction of gaseous Me3SiF with the in situ prepared Lewis acid Al(OR(F))3, the stable ion-like silylium compound Me3 Si-F-Al(OR(F))3 1 forms. The Janus-headed 1 is a readily available smart Lewis acid that differentiates between hard and soft nucleophiles, but also polymerizes isobutene effectively. Thus, in reactions of 1 with soft nucleophiles (Nu), such as phosphanes, the silylium side interacts in an orbital-controlled manner, with formation of [Me3Si-Nu](+) and the weakly coordinating [F-Al(OR(F))3](-) or [((F)RO)3Al-F-Al(OR(F))3](-) anions. If exchanged for hard nucleophiles, such as primary alcohols, the aluminum side reacts in a charge-controlled manner, with release of FSiMe3 gas and formation of the adduct R(H)O-Al(OR(F))3. Compound 1 very effectively initiates polymerization of 8 to 21 mL of liquid C4 H8 in 50 mL of CH2 Cl2 already at temperatures between -57 and -30 °C with initiator loads as low as 10 mg in a few seconds with 100% yield but broad polydispersities.

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Section: Comparison Of the Bonding Situation Between (Me3si)(etcb11fsupporting

confidence: 56%

A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me₃Si‐F‐Al(OR^F)₃

Rohde

Müller

Himmel

et al. 2014

Chemistry A European J

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“…Such observations, although weak in this case, are characteristic for C–H agostic interactions in transition metal complexes 53 , 54 but unusual as the source of structural deformation in p-block element chemistry. E–H σ-bond donor-acceptor interactions in the p-block were only observed for combinations of more hydridic bonds with the most Lewis acidic boranes, 55 , 56 silylium ions, 2 , 57 anagostic, 9 or structurally enforced. 58…”

Section: Resultsmentioning

confidence: 99%

An isolable, crystalline complex of square-planar silicon(IV)

Ebner

Greb

2021

Chem

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Our Earth's crust is covered with compounds of silicon(IV). In each, tetracoordinated silicon(IV) arranges its four substituents in a tetrahedral fashion, while other environments are unknown. This work describes the isolation and properties of a molecular complex with square-planar silicon(IV). The flattened structural motif provokes a range of features that primes the second most abundant element for new applications in catalysis and materials science.

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“…We may extend our comparisons also to other experimentally known dialkyl‐substituted silylium ions with rather different stabilization mechanisms (Figure 1). Table 5 shows that the by far lowest Lewis acidity is found for compound 6 ,10 which possesses a rigid structure and a cationic silicon center stabilized by two additional interactions with hydrogen atoms from the neighboring silyl groups. In contrast, the highest FIAs in this series are predicted for the hydrogen‐bridged disilyl cation, 4 ,9a and [FcSiMe 2 ] + .…”

Section: Resultsmentioning

confidence: 99%

“…Intramolecular 3c2e [Si⋅⋅⋅H⋅⋅⋅Si] + bridges delocalize the positive charge in such a way that steric shielding is not required anymore. Several congeners are known today (not shown),1 and the structure of 6 (Figure 1, lower right) is particularly noteworthy 10. In all these cases, coordination of neither solvent nor counteranion is an issue.…”

Section: Introductionmentioning

confidence: 99%

The Family of Ferrocene‐Stabilized Silylium Ions: Synthesis, ²⁹Si NMR Characterization, Lewis Acidity, Substituent Scrambling, and Quantum‐Chemical Analyses

Müther

Hrobárik

Hrobáriková

et al. 2013

Chemistry A European J

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The purpose of this systematic experimental and theoretical study is to deeply understand the unique bonding situation in ferrocene-stabilized silylium ions as a function of the substituents at the silicon atom and to learn about the structure parameters that determine the (29)Si NMR chemical shift and electrophilicity of these strong Lewis acids. For this, ten new members of the family of ferrocene-stabilized silicon cations were prepared by a hydride abstraction reaction from silanes with the trityl cation and characterized by multinuclear (1)H and (29)Si NMR spectroscopy. A closer look at the NMR spectra revealed that additional minor sets of signals were not impurities but silylium ions with substitution patterns different from that of the initially formed cation. Careful assignment of these signals furnished experimental proof that sterically less hindered silylium ions are capable of exchanging substituents with unreacted silane precursors. Density functional theory calculations provided mechanistic insight into that substituent transfer in which the migrating group is exchanged between two silicon fragments in a concerted process involving a ferrocene-bridged intermediate. Moreover, the quantum-chemical analysis of the (29)Si NMR chemical shifts revealed a linear relationship between δ((29)Si) values and the Fe···Si distance for subsets of silicon cations. An electron localization function and electron localizability indicator analysis shows a three-center two-electron bonding attractor between the iron, silicon, and C'(ipso) atoms, clearly distinguishing the silicon cations from the corresponding carbenium ions and boranes. Correlations between (29)Si NMR chemical shifts and Lewis acidity, evaluated in terms of fluoride ion affinities, are seen only for subsets of silylium ions, sometimes with non-intuitive trends, indicating a complicated interplay of steric and electronic effects on the degree of the Fe···Si interaction.

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Persistent Silylium Ions Stabilized by Polyagostic SiH⋅⋅⋅Si Interactions

Cited by 17 publications

References 71 publications

A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me₃Si‐F‐Al(OR^F)₃

A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me₃Si‐F‐Al(OR^F)₃

An isolable, crystalline complex of square-planar silicon(IV)

The Family of Ferrocene‐Stabilized Silylium Ions: Synthesis, ²⁹Si NMR Characterization, Lewis Acidity, Substituent Scrambling, and Quantum‐Chemical Analyses

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Persistent Silylium Ions Stabilized by Polyagostic SiH⋅⋅⋅Si Interactions

Cited by 17 publications

References 71 publications

A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me3Si‐F‐Al(ORF)3

A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me3Si‐F‐Al(ORF)3

An isolable, crystalline complex of square-planar silicon(IV)

The Family of Ferrocene‐Stabilized Silylium Ions: Synthesis, 29Si NMR Characterization, Lewis Acidity, Substituent Scrambling, and Quantum‐Chemical Analyses

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Product

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A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me₃Si‐F‐Al(OR^F)₃

A Janus‐Headed Lewis Superacid: Simple Access to, and First Application of Me₃Si‐F‐Al(OR^F)₃

The Family of Ferrocene‐Stabilized Silylium Ions: Synthesis, ²⁹Si NMR Characterization, Lewis Acidity, Substituent Scrambling, and Quantum‐Chemical Analyses