Base—Stabilized Silyliums

University of Bordeaux, Institute of Molecular Sciences, Talence, France 

Efficient Methods for Preparing Silicon Compounds. http //dx.doLoi l0.1016/B978-0-12-803530-6.00003-2 

Preparation of the silylium ion was carried out through the abstraction of the hydrogen of the silane, following the Bartlett— Condon—Schneider hydride transfer reaction first reported in the silicon series by Corey (12,13). Trityl reagents having a weakly coordinating anion are generally used to fully convert the silane. 

A dry J. Young NMR tube, syringe (1 mL), safety glasses, laboratory coat, and protective gloves. 

In a dryj. Young NMR tube was added the tert-butyl(2 -methoxy-[l,l -binaphthalen]-2-yl)(methyl)silane (20 mg, 0.052 mmol). The solid was dried under vacuum for 1 h, flushed with argon, and transferred into a glove box filled with argon. Dichloromethane-d2 (0.25 mL) was added, followed by a solution of Ph3C+[B(C6F5)4l (50 mg, 0.052 mmol) in dichloromethane-d2 (0.25 mL). The tube was sealed and subjected to NMR measurements. 

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Detailed mass spectrometry data (El, 50 eV) were recorded for l,3-diaza-2-silacyclopentane 8. The molecular ion peak has only small intensities (5%) and for the base peak, the mass of the stabilized silylium ion 45 is detected <2004IC3537>. Similar results were obtained for other diazasilacyclopentanes <20040M1180>. 

The synthesis of 61 by Lambert and Zhao [135] proofs that it is possible to generate free silylium cations in solution. The success of this work is based on fulfilling the requirements listed in section 8, namely (1) internal stabilization of the cation, (2) steric blocking of the Si+ center, (3) use of a weakly nucleophilic solvent with (4) not too small solvent molecules, and (5,6) use of bulky, weakly coordinating counterions with delocalized anionic charge. 

Donor-acceptor interactions between the electrophilic Si atoms of three-coordinate silicon derivatives and suitable bases lead to an effective stabilization of these usually extremely reactive systems. Thus, for example, silenes and silanimines have been shown to be stabilized by tertiary amines [1]. Extraordinary stabilizations have been achieved by intramolecular Si-N coordinations, making possible the isolation of stable silanethiones [2] and silylium salts [3]. Intramolecularly donor-stabilized silenes have been unknown till now, possibly because of the lack of suitable synthetic methods. 

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