Sila anions

In 1989 we reported on the synthesis and structure of the first l,3-diphospha-2-sila-allylic anion 3a [4], mentioning its value as a precursor for phosphino-silaphosphenes. In analogy to 3a we obtained the anions 3b-f [5] by treatment of 4 equivalents of the lithium phosphide 1 with the adequately substituted RSiC, of which 3b and 3c were investigated by X-ray analyses. The very short P-Si bond lengths (2.11-2.13 A) of 3a-c and the almost planar arrangement of Pl-Sil-P2-Lil indicate the cr-character of the Lithium P-Si-P allyl complex. 

A different approach toward highly substituted pyrroles involving a one-pot sila-Stetter/Paal-Knorr strategy was realized by Bharadwaj and Scheidt (Scheme 6.182) [343]. In this multicomponent synthesis, catalyzed by a thiazolium salt, an acyl anion conjugate addition reaction of an acylsilane (sila-Stetter) was coupled in situ with the conventional Paal-Knorr approach. Employing microwave conditions at 160 °C for 15 min, the acylsilane was combined with the cx/l-unsaturated ketone in... 

Phenylthio-l-trimethylsilylalkanes are easily prepared by the alkylation of (phenylthioXtrimethylsilyl)mcthane as shown in Scheme 10 [40], The treatment of (phenylthio)(trimethylsilyl)methane with butyllithium/tetramethylethylene-diamine (TMEDA) in hexane followed by the addition of alkyl halides or epoxides produces alkylation products which can be oxidized electrochemically to yield the acetals. Since acetals are readily hydrolyzed to aldehydes, (phenylthioXtrimethylsilyl)methane provides a synthon of the formyl anion. This is an alternative to the oxidative transformation of a-thiosilanes to aldehydes via Sila-Pummerer rearrangement under application of MCPBA as oxidant [40, 41]. 

An unexpected elimination of cyclopentadienide anion results on reaction of sila-cyclohexadienes with an extremely hindered aryllithium. ... 

The attempted reduction of 9,10-disila-9,10-dihydroanthracene (VIII R = H) led to immediate decomposition with the evolution of gas and an ESR spectrum due to several radicals including biphenyl radical anion. Similar results were obtained for 9-sila-9,10-dihydroanthracene (IX R = H) (89). Reduction of 9,9-dimethyl-9-sila-9,10-dihydroanthracene (IX R = Me) gave rise to an anion radical for which three unassigned couplings of 3.2, 2.6, and 0.7 G are reported (89). 

Formaldehyde anion synthon ( CHO). The anion of 1 (n-BuLi, THF, 0°) is readily alkylated, particularly by primary halides. The products can he converted into aldehydes under very mild conditions. Oxidation with m-chloroperbenzoic acid gives an unstable sulfoxide, which undergoes an sila-Pummerer rearrangement to an acetal. Addition of water liberates the free aldehyde. Epoxides can also be used as electrophiles.2 3 Example ... 

The iron complex 73 is prepared from the germolyl anion and iron(ll) chloride <20020M1734>. This complex 73 can be further lithiated with MeLi to 74 and elimination of Li[Si(SiMc3)3] gives the l,l -sila-[l]-l,l -digermaferro-cenophane 75 <20020M1734>. 

Anionic [RSi]4 (with R = Bu MeSi) has been reported recently and described as a sila analog of the cyclobutadiene dianion." ... 

Ml he anionic RING-OPENING POLYMERIZATION of 1,1-dimethyl-1-silacyclo-pent-3-ene (I) has been reported recently, although the polymer has not been fully characterized (i). The properties of poly(1,1-dimethyl-l-sila-d5-pent-3-ene) (H), as well as several related systems, are reported in this chapter. 

Allyloxysilyl)lithiums undergo a [2,3]Wittig-type rearrangement smoothly to form allylsilanolate anions in an intramolecular fashion (Scheme 11). This is the first example of the sila-Wittig rearrangement (54g). 

The electrochemical reduction of R2SiCl2 in the presence of 2,3-dimethylbutadiene proceeds smoothly to give the sila-cyclopentene derivatives [Eq. (53)] [193]. Probably the initial reduction of R2SiCl2 produces an silyl anion, which adds to the 1,3-diene. The intramolecular displacement reaction of the resulting allylic carbanion with the chlorosi-lane moiety gives the cyclized product. 

Syntheses, structures, and reactions of anions and dianions of sila-, germa-, stanna-, and plumba-cyclopentadienes and related benzannulated systems 04YGK790. 

Sila- and 1,3-disila cyclobutanes possess an increased reactivity because of their ring strain [106] and can be transformed into polycarbosilanes by ring opening polymerization using either thermal activation [107], anionic polymerization with organolithium compounds [108], or mostly platinum [109] or other late transition metal catalysts [110]. 

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