Of phenylsilanes

Diiodosilane l2SiH2 1872, prepared by treatment of phenylsilane PhSiHs with iodine, via PhSiH2l, in the presence of catalytic amounts of ethyl acetate at -20 °C, is much more electrophilic than Me3SiI 17 and therefore converts secondary alcohols such as 2-octanol 1871, at room temperature with Walden inversion, into iodides such as 1873 in 93% yield whereas the diol 1874 is nearly quantitatively converted into the monoiodobutane 1875 and only traces of the diiodobutane 1876 [88, 89] (Scheme 12.26). 

Normally, no small cyclopolysilanes are observed in these reactions. Two exceptions we have noted are the very slow reaction of phenylsilane under the influence of Cp2TiMe2 and the reaction of benzylsilane under the influence of dimethyltitanocene at very long reaction times. From both of these reactions we isolate a single isomer of the cyclohexasilane, in ca. 10 per cent yield in the case of the phenylsilane and ca. 60 per cent yield in the case of the benzylsilane. These isomers are believed to be the all-trans isomers. The phenyl derivative is identical to that... 

The compounds 2 and 3, have all been isolated from reactions of phenylsilane with either dimethyltitanocene (1 2) or dimethyl-zirconocene (r ). All of the evidence points to the fact that these compounds are probably resting species and are not involved in the catalytic cycle. They do nevertheless give some indication of the complex series of reactions that transform the dimethyl-metallocene to active catalyst. 

Fig.40a-c Silicon-29 and proton spectra of phenylsilane PhSiH3 in C6D6. a INEPT spectrum with complete proton decoupling, b proton-coupled INEPT spectrum l]sm 200 Hz) the fine structure is due to coupling with the aromatic protons, c proton spectrum showing 29Si satellites for the SiH protons)... 

Figure 4. Schematic of torsional energy levels in Si electronic state of phenylsilane and Do electronic state of phenylsilane+. The torsional state symmetry labels arise under the molecular symmetry group G12.

Figure 6. ZEKE-PFI spectra of phenylsilane (Do) taken with (Oi fixed on three S1-S0 bands as indicated and 2 scanned through the low-energy manifold of cation states.

The initial electron transfer to form the anion radical species seems to be reversible. For example, Allred et al. investigated the ac polarography of bis(trimethylsilyl)benzene and its derivatives which showed two waves in di-methylformamide solutions [71] the first one is a reversible one-electron wave, and the second one corresponds to a two-electron reduction. Anion radicals generated by electrochemical reduction of arylsilanes have been detected by ESR. The cathodic reduction of phenylsilane derivatives in THF or DME at — 16° C gives ESR signals due to the corresponding anion radicals [5] (See Sect. 2.2.1). 

The reagent is obtained as a fairly pure oil by reaction of phenylsilane with iodine catalyzed by a trace of an organic ester. After removal of volatile side products (benzene and HI), the oil can be purified by fractional distillation. 

The deformation of the benzene ring in substituted benzenes is a sensitive indicator of substituent effects. Extensive experimental evidence accumulated over the past two decades, mainly from X-ray diffraction studies of solid state samples However, the first report of a ring distortion in a benzene derivative was done by Keidel and Bauer in their pioneering (1956) gas-phase electron diffraction study of the molecular structure of phenylsilane Recently a... 

We describe herein the synthesis of iodosilane by the reaction of phenylsilane with hydrogen iodide and the preparation of the methylated iodosilanes, namely (CH3) SiH3 I (n = 0-3), by the reaction of the parent hydride with hydrogen... 

The cleaveage of phenylsilane with hydrogen iodide also provides of iodosilane (based on details given in Reference 15). 

Lanthanide-catalyzed enyne cyclization/hydrosilylation was also applied to the synthesis of silylated alkylidene cyclohexane derivatives. For example, reaction of the 3-silyloxy-l,7-enyne 17 with methylphenylsilane catalyzed by Gp 2YMe(THF) at 50°G for 8h gave 18 in quantitative yield as a 4 1 mixture of trans cis isomers (Equation (11)). Employment of methylphenylsilane in place of phenylsilane was required to inhibit silylation of the initially formed yttrium alkenyl complex, prior to intramolecular carbometallation (see Scheme 8). 

Arylsilane radical anions undergo cleavage and coupling reactions, usually under conditions where excess reducing agent is available. Reduction of phenylsilane, diphenylsilane, or triphenylsilane with sodium-potassium alloy under preparative conditions gives high yields of tetraphenylsilane (7). In the reduction of phenylsilanes, the appearance of 1,4-bis(silyl)benzene radical anions is frequently observed (135, 35, 86, 97, 75, 120, 100). Typical results are shown in Table II. 

Sign of rotation. h With 1.1 equiv of phenylsilane to imine. TBDMS = f-C4H9(CH3)2Si. ... 

The phenylsilyl cation CgHsSi 4 (85) and its interconversion to other possible isomers such as the silacylcoheptatrienyl cation (86) have attracted considerable experimental as well as theoretical interest in view of the possible similarities or differences of the well-known benzyl and cycloheptatrienyl cations243 and their silicon analogues. Thus, Beauchamp and coworkers244,245 have found that electron ionization of phenylsilane gives rise to both isomers 85 and 86, which do not interconvert at room temperature and can be readily distinguished by their ion-molecule reactions. 

A domino reduction-aldol reaction of ketones with methyl acrylate produces tertiary alcohols bearing an ester group (51) in high ee and de.151 Using a diphosphine- modified copper fluoride complex in the presence of phenylsilane, the method avoids having to preactivate the nucleophile prior to the C—C bond-forming step. 

Woo recently developed a rapid, highly linear-selective dehydrocoupling catalyst system of phenylsilane CpjMCL/Hydride (C p = C5H5 or C5Me5 M = Ti, Zr, Hf Hydride = Red-Al, Selectride, Super Hydride) combination catalysts [Eq. (2)].11,17... 

Insoluble solid polymers were isolated in 82% yield for Ti, 95% yield for Zr, and 80% yield for Hf. TGA ceramic residue yields were 72% for Ti, 73% for Zr, and 74% for Hf. The weight average molecular weights of the oily polymers were 4120 for Ti, 9020 for Zr, and 5010 for Hf. The TGA ceramic residue yields of the soluble oily polymers were ca. 14%. The dehydrocoupling mechanism of 4 should be similar to the sigma-bond metathesis for the dehydrocoupling of phenylsilane.11,12... 

The readily available yttrocene derivative (C5Me5)2YMe(THF) has been shown to be an effective catalyst for the hydrosilylation of internal alkynes [85]. A single stereoisomer, i.e. the product of cis addition of phenylsilane to the alkyne, is formed in the reaction with symmetrically substituted alkynes. Comparable reactions with a variety of unsymmetrically substituted internal alkynes resulted in a regioselective hydrosilylation reaction in which the silane moiety is placed at the sterically less hindered carbon atom of the alkyne. Various functional groups such as halides, amines, protected alcohols, and trisubstituted... 

This behavior reflects the high basicity of the silylated carbon and, in fact, protonation of phenylsilane and aryltrimethylsilanes yields the //mo-protonatcd species as the... 

Birchall, T., Drummond, I. Nuclear magnetic resonance spectra of phenylsilane, phenylgermane, and their anions Comments on the relative acidities of phenylgermane and germane. J. Chem. Soc. (A) 1970, 1401-05. 

The functionalization of polymers is another useful feature of the hydrosilation reaction. The introduction of highly fluorinated alkyl chains by the hydrosilation of Si-H groups of the polymer with fluorinated aUcenes is a typical example. Poly(phenylsilanes) obtained by the dehydrocouphng polymerization of phenylsilane undergo AIBN initiated free radical hydrosilation with aUcenes, ketones and aldehydes. Cross-linking and branching of polymers can also be easily accomplished using hydrosilation. 

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