Synthesis and Reactivity of the First Isolated Hydrogen‐Bridged Silanol–Silanolate Anions

We report on the first examples of isolated silanol–silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol–silanolate anions are postulated intermediates in the hydroxide‐mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization.     

Easy saponification by metal silanolates: application in SPPS and in (S)-5-hydroxynorvaline preparation

Alkali metal trimethylsilanolates, TMSO⁻, M⁺, has been used for efficient conversion of methyl esters into their corresponding anhydrous acid salts under mild non-aqueous conditions. This strategy has been applied to SPPS for the preparation of neurotoxin cyclic analogues and in (S)-5-hydroxynorvaline synthesis.     

Tris(pentafluoroethyl)silanol Derivatives and the Lewis Amphoteric Tris(pentafluoroethyl)silanolate Anion, [Si(C2F5)3O]−

While alkyl-substituted siloxanes are widely known, virtually nothing is known about perfluoroalkyl siloxanes and their congener species, the silanols and silanolates. We recently reported on the tris(pentafluoroethyl)silanide ion, [Si(C₂F₅)₃]⁻, which features Lewis amphoteric character deriving from the pentafluoroethyl substituents and their strong electron-withdrawing properties. Transferring this knowledge, we investigated the Lewis amphoteric behavior of the tris(pentafluoroethyl)silanolate, [Si(C₂F₅)₃O]⁻. In order to examine such Lewis amphoteric behavior, we first developed a strategy for the synthesis of the corresponding silanol Si(C₂F₅)₃OH, which readily condenses at room temperature to the hexakis(pentafluoroethyl)disiloxane, (C₂F₅)₃SiOSi(C₂F₅)₃. Deprotonation of Si(C₂F₅)₃OH employing a sterically demanding phosphazene base allows the characterization of the first example of a dimeric triorganosilanolate: the dianionic hexakis(pentafluoroethyl)disilanolate, [{Si(C₂F₅)₃O}₂]²⁻, implies Lewis amphoteric character of the monomeric [Si(C₂F₅)₃O]⁻ anion.     

Palladium-catalyzed cross-coupling reactions of silanolates: a paradigm shift in silicon-based cross-coupling reactions

This paper chronicles the conceptual development, proof of principle experiments, and recent advances in the palladium-catalyzed cross-coupling reactions of the conjugate bases of organosilanols. The discovery that led to the design and refinement of this process represents a classical illustration of how mechanistic studies can provide a fertile ground for the invention of new reactions. On the basis of a working hypothesis (which ultimately proved to be incorrect) and the desire to effect silicon-based cross-coupling without the agency of fluoride activation, a mild and practical palladium-catalyzed cross-coupling of alkenyl-, aryl-, and heteroaryl silanolates has been developed. The mechanistic underpinnings, methodological extensions, and the successful applications of this technology to the synthesis of complex molecules are described.     

1,2-Dimethyl-1,2-diphenyidisilane-1,2-diol and its K,Na, and FeII derivatives. Molecular structure of the all-trans-isomer, 2,3,5,6-tetra-methyl-2,3,5,6-tetraphenyl-1,4-dioxa-2,3,5,6-tetrasilacyclohexane

Hydrolysis of 1,2-dimethyl-1,2-diphenyl-1,2-dichlorodisilane yields 1,2-dimethyl-1,2diphenyldisilane-1,2-diol, which undergoes dimerization into stereoisomeric 2,3,5,6-tetramethyl-2,3,5,6-tetraphenyl-1,4-dioxa-2,3,5,6-tetrasilacyclohexanes under the action of H₂SO₄. Pure all-trans-isomer has been isolated and characterized by¹H NMR and IR spectroscopy and X-ray analysis. The reaction of sodium disilanediolate with FeBr₂ results in the formation of 1,2-dimethyl-1,2-diphenyl-4-ferra(ii)-3,5-dioxa-1,2-disilacyclopentane.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2550–2556, October, 1996.     

The Influence of Weakly Coordinating Cations on the O−H⋅⋅⋅O− Hydrogen Bond of Silanol-Silanolate Anions

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol-silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol-silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate–oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol-silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol-silanolate chains in the solid state.     

Synthese und Struktur von Vanadium(III)- und Vanadium(IV)-silanolaten

Synthesis and Structures of Vanadium(III) and Vanadium(IV) Silanolates The syntheses of the new and partially known vanadium(III)-silanolate complexes [{V(OSiMe^t₂Bu)₃}₂(THF)] ( 1 ), [Li(THF)₂V(OSiMe^t₂Bu)₄] ( 2 ), [V(OSiMe^t₂Bu)(lut)] ( 3 ), V(OSiPh₃)₃(THF)₃ ( 4 ), [Li(THF)₄][V(OSiPh₃)₄](THF)₂ ( 5 ), [Li(DME)VMes(OSiMe^t₂Bu)₃] ( 7 ), [Li(THF)₄][VMes · (OSiPh₃)₃] ( 8 ), [Li(THF)₄][VMes₃(OSiMe^t₂Bu)] ( 9 ), and Na[VMes₃(OSiPh₃)](THF)₄ ( 10 ) as well as the vanadium(IV) compounds [V(OSiPh₃)₄] ( 6 ), [VMes₃(OSiMe^t₂Bu)] ( 11 ) and [VMes₃(OSiPh₃)] ( 12 ) are reported. In most cases the vanadium atom displays a coordination number of four. The dimeric structure of 1 with coordination numbers of four and five, respectively, has been deduced from molecular mass measurements, mass spectrometry and its magnetic properties. The crystal structures of compounds 2 , 4 , 5 , 9 and 11 were resolved. Complex 2 resembles a bridged contact ion pair in which both metal centres are in a tetrahedral coordination environment. In 4 the ligands are arranged trigonal bipyramidally with the THF molecules in the axial positions. Complexes 5 and 9 crystallize in separated ion paires with the vanadium in a tetrahedral coordination sphere. The crystal structure of 11 is analogous to that of 9 but with consequences due to the higher oxidation state. Oxidation of the vanadates(III), e. g. 5 , 9 and 10 , yields the corresponding vanadium(IV) compounds 6 , 11 and 12 .     

Lithium and sodiumtris(trimethylsilyl)silanolates. Synthesis and reactivity

Lithium and sodium tris(trimethylsilyl)silanolates were obtained by the reaction of tris(trimethylsilyl)silanol with BuⁿLi or PrⁱONa in hexane. The degree of association of silanolates in benzene solution was found to be 2 and 4 for the sodium and lithium derivatives, respectively. (Me₃Si)₃SiONa is noticeably more active than the lithium derivative in the reaction with Me₃SiCl. Tris(trimethylsilyl)silanol reacts with trimethylchlorosilane to give (Me₃Si)₃SiCl. The hydrolysis of (Me₃Si)₃SiONa (Li) in benzene and hexane yields the corresponding silanol, whereas in HMPA the splitting of Si-Si bonds and hydrogen evolution were observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1146–1149, June, 1995.This work was carried out with financial support from the International Scientific and Technical Center (Project No 015-94).