17988-20-4Relevant articles and documents
Nucleophile-assisted cleavage of benzyltrialkylsilane cation radicals
Dockery, Kevin P.,Dinnocenzo, Joseph P.,Farid, Samir,Goodman, Joshua L.,Gould, Ian R.,Todd, William P.
, p. 1876 - 1883 (1997)
The cation radicals of benzyltrialkylsilanes have been generated using photoinduced electron transfer and characterized using transient absorption spectroscopy. Absolute rate constants for nucleophile-assisted C-Si bond cleavage have been determined, for different nucleophiles in different solvents and with different substituents on the phenyl ring. The short lifetime (-9 s) of the parent benzyltrimethylsilane cation radical in acetonitrile was unambiguously shown to be due to a rapid nucleophile-assisted bond cleavage, with the solvent acting as the nucleophile. Even in less polar solvents, such as dichloromethane, the lifetime of benzyltrimethylsilane cation radical is quite short (ca. 20 ns) unless trace amounts of water, which acts as an efficient nucleophile, are removed. Consistent with the nucleophile-assisted cleavage mechanism for the benzyltrialkylsilanes, sterically-demanding substituents on silicon decrease the rate constant for cleavage by as much as 4 orders of magnitude, depending upon the nucleophile. Similarly, increasing steric crowding on the nucleophile also decreases the rate constant, although smaller changes in the rate constants are observed. Electron-donating substituents (4-methyl and 4-methoxy) on the phenyl group also lead to a substantial decrease in the rate constant for cleavage of the cation radicals. When measurements are performed in the least nucleophilic solvent and under conditions that minimize contributions from adventitious nucleophiles, the lifetimes of the cation radicals of the benzyltrialkylsilanes can be so long that the rate of pseudofirst-order decay can not be accurately determined. If the cation radicals undergo unimolecular C-Si bond cleavage (i.e., not nucleophile-assisted) under these conditions, the rate constant for this process is estimated to be less than 104 s-1.
Iron-catalyzed cross coupling of aryl chlorides with alkyl Grignard reagents: Synthetic scope and FeII/FeIV mechanism supported by x-ray absorption spectroscopy and density functional theory calculations
Agata, Ryosuke,Takaya, Hikaru,Matsuda, Hiroshi,Nakatani, Naoki,Takeuchi, Katsuhiko,Iwamoto, Takahiro,Hatakeyama, Takuji,Nakamura, Masaharu
supporting information, p. 381 - 390 (2019/02/25)
A combination of iron(III) fluoride and 1,3-bis(2,6-diiso-propylphenyl)imidazolin-2-ylidene (SIPr) catalyzes the high-yielding cross coupling of an electron-rich aryl chloride with an alkyl Grignard reagent, which cannot be attained using other iron catalysts. A variety of alkoxy-or amino-substituted aryl chlorides can be cross-coupled with various alkyl Grignard reagents regardless of the presence or absence of β-hydrogens in the alkyl group. A radical probe experiment using 1-(but-3-enyl)-2-chlorobenzene does not afford the corresponding cyclization product, therefore excluding the intermediacy of radical species. Solution-phase X-ray absorption spectroscopy (XAS) analysis, with the help of density functional theory (DFT) calculations, indicates the formation of a high-spin (S = 2) heteroleptic difluorido organoferrate(II), [MgX][FeIIF2(SIPr)-(Me/alkyl)], in the reaction mixture. DFT calculations also support a feasible reaction pathway, including the formation of a difluorido organoferrate(II) intermediate which undergoes a novel Lewis acid-assisted oxidative addition to form a neutral organoiron(IV) intermediate, which leads to an FeII/FeIV cata-lytic cycle, where the fluorido ligand and the magnesium ion play key roles.
Direct oxidation of the C(sp2)-C(sp3) bond from benzyltrimethylsilanes to phenols
Li, Wei,Gao, Guolin,Gao, Yuan,Yang, Chao,Xia, Wujiong
supporting information, p. 5291 - 5293 (2017/07/10)
A novel pathway for direct conversion of benzylsilanes to phenols by oxidation with Na2S2O8 and oxygen is efficiently developed under mild and neutral conditions. The reaction shows good functional group tolerance to afford phenols in moderate yields. The possible mechanism is proposed based on the isotopic labeling trials.
