Silyl Anions Research Articles

Alkoxides of <i>o</i>-silyl benzyl alcohols in cleavage reactions: approaches to benzyl and silyl anion equivalents

Alkoxides of <i>o</i>-silyl benzyl alcohols in cleavage reactions: approaches to benzyl and silyl anion equivalents

A novel α,ω silyl dianionic salt. The synthesis and characterization of remotely connected benzannulated silole monoanions

The novel dilithium salt of 1,2-bis((BPSI)2)ethane (BPSI = 3-butyl-2-phenyl-1-silaindenyl) 4 was prepared from the reaction of 2 with 1,2-bis(chloro-BPSI)ethane 3 and characterized by NMR spectroscopy and by X-ray crystallography. It is demonstrated that dianions of silicon not only can perform stepwise reactions but also that, when a quenching reagent possesses two remote electrophilic centers, they can be attacked separately and maintain single charges on the silicon centers. The two lithium ions in 4 are η1 -coordinated to two remote silyl anions. NMR and X-ray data are consistent with a low degree of π-electron delocalization in the C4Si ring.

Polysilyldianions — Synthesis and reactivity

Reaction of α,ω-bis[tris(trimethylsilyl)silyl]alkanes with one equivalent of potassium tert-butoxide resulted in clean formation of mono-potassium silyl anions. Addition of another equivalent of the transmetallating agent led to the formation of the di-potassium compounds. Partial hydrolysis of the di-potassium compounds induced an intramolecular reaction yielding a cyclic silyl potassium compound.

D0 Bis(silyl) Complexes Free of Anionic π-Ligands: Syntheses, Structures, and a Novel Exchange between Silyl Ligands and Silyl Anions

d⁰ Bis(silyl) Complexes Free of Anionic π-Ligands: Syntheses, Structures, and a Novel Exchange between Silyl Ligands and Silyl Anions

Recent developments in silicon interelement linkage: the case of functionalized silyllithium, silylenoid and sila-ylide

Abstract

UV-Visible and NMR Spectroscopic Studies of Disilanylene 1,2-Dianions. Questions of Charge Delocalization of Silyl Anions

Abstract The reaction of 1,2-dichloro-1,2-diisopropyl-1,2-disilaacenaphthene with an excess of alkali metal resulted in the formation of the corresponding dialkali metal, 1,2-disila-1,2-acenaphthenediide, as the disilanylene 1,2-dianion. UV-vis and NMR spectroscopic analyses strongly support the delocalization of the silyl anion.

Preparation of substituted network polysilanes by a disproportionation reaction of alkoxydisilanes in the presence of alkoxysilanes

Network methylethoxypolysilanes containing various substituents such as hexyl, phenyl, ethylene, hexamethylene, phenylene, and thiophene groups were prepared by a disproportionation reaction of 1,1,2,2-tetraethoxy-1,2-dimethyldisilane in the presence of the corresponding substituted alkoxysilanes. The reaction was considered to proceed via a silyl anion mechanism. The silyl anion produced from a disilane or a higher homologue attacked the alkoxysilane, and that caused the alkoxysilane moiety to be introduced into the polysilane. The amount of incorporated substituents varied from 3 to 29% of all organic substituents, depending on which alkoxysilane was reacted. The electrical conductivities of some polysilanes were measured, and the polymer with thiophene groups was found to show relatively higher conductivity of 10 -5 Scm -1 after iodine doping.

ChemInform Abstract: Synthetic Applications of Functionalized Silyl Anions: Aminosilyl Anions as Hydroxy Anion Equivalent.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Question of Aromaticity in the 1-Lithio-1-methyl-1-silafluorenide Anion. Evidence for a Localized Silyl Anion1

The Question of Aromaticity in the 1-Lithio-1-methyl-1-silafluorenide Anion. Evidence for a Localized Silyl Anion¹

Synthetic applications of functionalized silyl anions: Aminosilyl anions as hydroxy anion equivalent

An (aminosilyl)lithium and the corresponding copper and magnesium reagents serve as a hydroxy anion equivalent through (1) allylic substitution, (2) addition to vinyloxirane, and (3) addition to acetylene, followed by oxidative cleavage of the silicon-carbon bonds. Highly regio- and stereoselective transformations have been achieved in all cases. An (aminosily)lithium and the corresponding copper and magnesium reagents serve as a hydroxy anion equivalent. [Display omitted]

Anionic Ring-Opening Polymerization of 1,2,2-Trimethyl-1-phenyl-1,2-disilacyclopentane

The anionic ring-opening polymerization of 1,2,2-trimethyl-1-phenyl-1,2-disilacyclopentane took place in THF at 0∼−78°C. The initiators were nBu4NF, PhMe2SiK, and (PhMe2Si)2Cu(CN)Li2. When PhMe2SiK was used, the addition of HMPA was required for the polymerization. The polymerization initiated with (PhMe2Si)2Cu(CN)Li2 showed a living character to some extent. The product polymers contained not only a head-to-tail structure but also head-to-head and tail-to-tail structures, whose amounts were dependent on the initiator: 4% (nBu4NF), 30% (PhMe2SiK), and 12% ((PhMe2Si)2Cu(CN)Li2). These values reflect the efficiency of the phenyl group to stabilize the silyl anion that is the propagating end.

Thermal degradation of poly(methyl‐n‐hexylsilylene)

AbstractThermal degradation of poly(methyl‐n‐hexylsilane) in the solid state in absence of oxygen reveals formation of a cyclic pentamer between 150 and 250°C. Polymer is gradually degraded to an intermediate molecular weight distribution. The weight average of this new distribution is not only temperature‐dependent, but is also a function of viscosity of the polymer and nature of chain ends. As no insolubles or SiH groups are formed, the degradation mechanism is most likely a back‐biting mechanism induced by active chain ends such as silyl anions or SiCl rather than a homolytic cleavage of the main chain. A concurrent intramolecular rearrangement reaction is also proposed. Moreover, this study proposes an explanation to the trimodal molecular weight distribution obtained by the Wurtz coupling of dichlorosilanes with molten sodium in refluxing toluene. © 1995 John Wiley & Sons, Inc.

The Chemistry of Silylenoids: Preparation and Reactivity of (Alkoxysilyl)lithium Compounds

The ambiphilic reactivity exhibited by the silicon compound 1 contrasts the behavior of neutral silanes and simple silyl anions. This reactivtiy is an indication of silylenoid character, which can be accounted for by the two limiting electronic structures 1 a and 1 b.

Access to stabilized silyl anions by electroreduction of chlorosilanes

Using the sacrificial anode technique, the electroreduction of arylchlorosilanes into the corresponding arylhydrosilanes occurs via a silylaluminium intermediate characterized for the first time in such reactions.

Peculiarities in the cleavage by methyllithium of unsymmetrical disilanes

The title reactions did not produce the more stable silyl anions from the disilanes studied, they either occurred by attack at the more electrophilic silicon atom, or led to unexpected products.

(Trialkylstannyl)cuprates: A spectroscopic and chemical investigation

AbstractLow‐temperature 1H, 13C, and 119Sn NMR spectroscopic techniques were used to probe the nature of cuprates derived from Me3SnLi, CuCN, or CuBr · Me2S. In THF, addition of Me3SnLi and CuX (X = Br or CN) gives aggregated [Me3SnCu · LiX]n. When the ratio of stannyl anion to cuprous cation is 2 : 1, mixtures of (Me3Sn)3Cu2Li, (Me3Sn)2CuLi · LiX, and (Me3Sn)3CuLi2 are formed. This behavior is unlike either homo trialkylsilycyanocuprates, which form (R3Si)2Cu(CN)Li2 at 2 : 1 ratios of silyl anion to cuprous ion, or mixed trialkylstannyl‐ or trialkylsilyl‐cuprates, which exist as (R3M)Cu(R′)(CN)Li2 (M = Si or Sn and R′ = Me or Bu). (R3Sn)3CuLi2 is the major species when the stannyl anion to cuprous cation ratio reaches 3 : 1. On the other hand, the analogous magnesium cuprates are discrete species in solution and possess differential reactivity.

Some further observations on polymethylsilane as a precursor for silicon carbide

AbstractPoly(methylsilanes) produced by sodium coupling of methyldichlorosilane (2:1 molar ratio) contain residual chlorine which can be removed by reduction with LiAlH4 at low temperature. Following this reduction, the polymers contain catalytically active centers (presumed to be silyl anions) which, in THF solution, further polymerize and crosslink the polymer at room temperature, while in toluene solution they are inactive. The reduced polymethylsilane gives high yields (ca 75%) of ceramic product on pyrolysis, but the composition is rich in silicon, compared with pure silicon carbide (SiC). Addition of catalytic amounts of dimethylzirconocene (DMZ) to this polymer gives a product which pyrolyzes to a product with stoichiometry close to that of SiC. It is concluded that the DMZ has an important influence in promoting Si–C bond formation, relative to Si–Si bond formation, during the pyrolysis.

Low Temperature Wurtz-Type Polymerization of Substituted Dichlorosilanes

We have studied the heterogeneous Wurtz-type polymerization of a number of substituted dichlorosilanes at low temperatures as a function of solvent, metal reductant, reaction temperature, reagent stoichiometry, and additives. At 65°C, aryl dichlorosilanes rapidly produce polymer while dialkyl substituted monomers do not in the absence of additives. While the rate of polymerization of the former is relatively insensitive to steric effects, it is greatly reduced by the presence of electron donating substituents. Reaction temperature is an important variable with higher temperatures producing lower yields of multimodal products. At 65°C substituted dichlorosilanes produce high molecular weight products at low monomer conversions independent of reagent stoichiometry in a manner more consistent with a chain growth process. Polymerization in the presence of potential hydrogen donating solvents and additives produced no evidence for hydrogen atom chain transfer which would be expected if trappable silyl radicals are intermediates. The evidence is more consistent with silyl anions rather than silyl radicals as the propagating species in the heterogeneous polymerization.

Übergangsmetall-silyl-komplexe: XLVII. Deprotonierung der elektronenreichen hydrido-silyl-komplexe Fe(CO)2(dppe)(H)(SiR3) und Fe(CO)(dppe)H3(SiR3); darstellung der komplexe Fe(CO)2(dppe)(EMe3)(SiR3) und Fe(CO)(dppe)H2(EMe3) (SiR3) (E  Sn, Pb) aus den korrespondierenden anionischen komplexen

The hydridosilyl complexes Fe(CO)2(dppe)(H)[Si(OR)3] (R  Me, Et) and Fe(CO)(dppe)H3[Si(OEt)3] (dppe = Ph2PCH2CH2PPh2) were deprotonated with KH/18-crown-6 to give the anionic silyl complexes [K(18-crown-6)][Fe(CO) 2(dppe){Si(OR)3}] (2) and [K(18-crown-6)] [Fe(CO)(dppe)H2{Si(OEt)3}] (4), respectively. Reaction of 2 with Me3ECl (E  Sn or Pb) affords the octahedral complexes Fe(CO)2(dppe)(EMe3)[Si(OR)3] with trans-CO ligands. From 4 and Me3ECl the complexes Fe(CO)(dppe)H2(EMe3)[Si(OEt)3] are formed. Spectroscopic data suggest that those complexes have a capped octahedral geometry, in which the dppe ligand, ER3 and CO are in plane, one hydride ligand is in an axial position and the other hydride caps a triangular face.

Negative hyperconjugation in methyl and silyl anions and its effect on the acidities of CH (4- n) F n CH (4- n) C1 n SiH (4- n) F n and SiH (4- n) Cl n

Group separation reactions calculated using an ab intio molecular orbital calculation at the MP4/6-31 + + G(d,p) level of theory, show the negative hyperconjugation between fluorine atoms to be larger in methanes than in silanes. Stabilisation due to negative hyperconjugation is larger in anions than in identically substituted neutral molecules, e.g. 43.1 kcal mol −1 in CF 3 − compared with 26.7 kcal mol −1 in CHF 3. By contrast, in chloro-substituted methanes, silanes, methyl anions and silyl anions, group separation energies are approximately zero, indicating no appreciable negative hyperconjugation. An α-chloro substituent is more effective than an α-fluoro one at delocalising the negative charge of an anion and, as a consequence, the chloromethanes and chlorosilanes are all more acidic than the identically substitued fluoromethanes and fluorosilanes. For chloro-substituted molecules the acidity is linearly dependent on the number of chlorine atoms; for fluoro-substituted molecules stabilisation by negative hyperconjugation results in each additional fluorine atom increasing the acidity by larger increments.