Silanes silols

Table 3 lists PAEs containing Si, Fe, and B. Silole containing Si in the five-mem-bered ring [157] has a low transition energy because of its low LUMO level [158], and its homopolymers have been prepared [159, 160]. 2,5-Dili-thiosiloles, which can be prepared by the ring-closing reaction of diethynyl-silane, serve as starting materials for various 2,5-disubstituted siloles such as 2,5-dibromosiloles and 2,5-di(trialkylstannyl)siloles [161,162]. PAEs with the silole ring have been reported as shown in Nos. 1-4 in Table 3. PAE-type polymers with Si atoms in the main chain have also been prepared (Nos. 12-16), and their optical properties including photoconductivity have been revealed [155,156].

An extensive theoretical investigation does not exist for the siloles, but PM3 calculations of formation enthalpies of 2 and its tautomers have indicated that the l//-silole is the most thermodynamically stable species200. The activation barrier for 11 — 2 isomerization was calculated to be 96 kJ moC1, comparable to that for cyclopentadiene2d 116. The (1H + 1H) dimer 1019 is isolated rather than the (2H + 1H) dimer as in the case of phosphole. This directly confirms the thermodynamic stability and the Diels-Alder kinetic instability of 2. The marked difference in the stability of the parent silole and phosphole was explained3 by the relative stabilities of the a bonds in silanes and phosphines (Si > P) and of the ji bonds in silenes and phosphenes (P > Si)117. 

Tetrasubstituted silanes are also sources of silylene. Suginome and coworkers reported that palladium catalyzed the transfer of dimethylsilylene, formed from silylborane 44, to alkynes [equation (7.8)], 60 Exposure of silylborane 48 and alkyne 49 to substoichiometric amounts of palladium and P(7-Bu)2(2-biphenyl) afforded 2,4-disubstituted silole 50. This process tolerates a variety of functionality including silyl ether-, dimethylamino-, and trifluoromethyl groups. In addition to aliphatic terminal acetylenes, arylacetylenes were also competent substrates. For... 

While some of the reactions mentioned above can be used for the synthesis of 1,1-difunctionalized siloles30, none of them can afford 2,5-difunctionalized siloles. 2,5-Difunctionalized siloles can be directly prepared only by route B. Wrackmeyer has reported that a reaction of bis(stannylethynyl)silanes 8 with BR3 (R = Me, Et, i-Pr, and n-Bu) affords 2,5-distannyl-3-borylsiloles 9 (equation 3)31. We have recently reported a general synthesis of 2,5-difunctionalized siloles by the intramolecular reductive cyclization of diethynylsilanes (equation 4)32. Thus, the reaction of bis(phenylethynyl)silanes 10 with lithium naphthalenide affords 2,5-dilithiosiloles 11, which can be further transformed into a variety of 2,5-difunctionalized siloles 12. In addition, starting from bis(phenylethynyl)diaminosilanes 13, various 1,1-difunctionalized siloles 15 are also accessible through 1,1-diaminosiloles 14 (equation 5)33. With these functionalized siloles in hand, various silole-based <7- and jr-con jugated compounds have been prepared as described below. 

The analogous reaction with trichloro(phcnylethynyl)silane affords the silole 171. On the other hand, trichloro-vinylsilane reacts with dilithioderivative 170 in the ratio 2 1 forming silacycloheptadiene 172 <2000CC697>. 

In the presence of an excess of trimethyl(vinyl)silane, the olefmic Rh complex 191 slowly undergoes rearrangement to the complex 66, containing an 7] -coordinated silole ligand <1999JA4385>. 

Ni-catalyzed cleavage of the Si-Si bond in the pseudo-pentacoordinated silane 192 leads to a short-lived silylene species which is trapped by an excess of tolane to give the silole 193 <1996JOM(521)325>. 

Diethynyl(dimethyl)silane, Me2Si(C C-H)2 47, reacts slowly at 80-90 °C with BEt3 to give the silole 48 which, however, undergoes fast various [4-1-2] cycloadditions (see Section 3.17.4.3.1) <2002ZNB741>. 

Two alkynes molecules are gathered by the Pd catalyst to react with diaUcylamino-(pinacolatoboryl)silanes, consequently 2,4-disubstituted siloles are produced. ... 

Once more most of the pertinent chemistry reported centres upon siloles and parallels that are generally associated with silanes. Apart from those encountered in Section 2.17.4.3 the more common conversions encountered are summarized in Table 1 along with appropriate references. 

This reaction was first reported by Peterson in 1968. It is a two-step synthesis of olefin involving the addition of an a-silyl carbanion to a carbonyl compound to form y3-silyl alcohol (or /3-hydroxy silane) and the elimination of silol. Therefore, this reaction is generally known as the Peterson olefination. In addition, this reaction is also referred to as the Peterson reaction " and Peterson elimination. Occasionally, the Peterson olefination is also called the Peterson alkenation or Peterson alkenylation. ... 

TTie first general synthetic route to 2,5-difunctionaUzed siloles is the intramolecular reductive cyclization of diethynylsilanes [10]. Thus, the reduction of bis(phenylethynyl)silane 1 using an... 

Scheme 1. Synthesis of 2,5-difunctionalized siloles 4 by reduction of bis(phenylethynyl)silane 1...

Poly(silole-silane)s have been prepared by Sakurai and coworkers [114]. These copolymers contain a silole unit along with silane units that are con-... 

Hies L, Tsuji H, Sato Y, Naktunura E (2008) Modular synthesis of functionalized benzosUoles by tin-mediated cyclization of (o-alkynylphenyl)silane. J Am Chem Soc 130 4240-4241 Hies L, Tsuji H, Nakamura E (2009) Synthesis of benzo[b]siloles via KH-promoted cyclization of (2-alkynylphenyl)silanes. Org Lett 11 3966-3968... 

In 1993, Ikenaga et al. reported efficient silole synthesis using readily prepared (trialkylstannyl)hydrosilanes as a silylene source [30]. Silanes 75 reacted with various terminal alkynes 74 at room temperature to afford 3,4-disubstituted siloles 76 as a major regioisomer (Scheme 6.22). 

Silafluorene exhibited superior reactivity for the double trans hydrosilylation, giving spirocyclic silole in 79% yield. The use of diethylsilane and methyl(phenyl)silane as hydrosilylation agents was unsuccessful. 

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