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The power of trichlorosilylation: isolable trisilylated allyl anions, allyl radicals, and allenyl anions.

ABSTRACT: Treatment of hexachloropropene (Cl₂C[double bond, length as m-dash]C(Cl)-CCl₃) with Si₂Cl₆ and [nBu₄N]Cl (1 : 4 : 1) in CH₂Cl₂ results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [nBu₄N][Cl₂C[double bond, length as m-dash]C(SiCl₃)-C(SiCl₃)₂] ([nBu₄N][1]). Tetrachloroallene Cl₂C[double bond, length as m-dash]C[double bond, length as m-dash]CCl₂ was identified as the first intermediate of the reaction cascade. In the solid state, [1]^- adopts approximate C _s symmetry with a dihedral angle between the planes running through the olefinic and carbanionic fragments of [1]^- of C[double bond, length as m-dash]C-Si//Si-C-Si = 78.3(1)°. One-electron oxidation of [nBu₄N][1] with SbCl₅ furnishes the distillable blue radical 1˙. The neutral propene Cl₂C[double bond, length as m-dash]C(SiCl₃)-C(SiCl₃)₂H (2) was obtained by (i) protonation of [1]^- with HOSO₂CF₃ (HOTf) or (ii) H-atom transfer to 1˙ from 1,4-cyclohexadiene. Quantitative transformation of all three SiCl₃ substituents in 2 to Si(OMe)₃ (2 ^OMe) or SiMe₃ (2 ^Me) substituents was achieved by using MeOH/NMe₂Et or MeMgBr in CH₂Cl₂ or THF, respectively. Upon addition of 2 equiv. of tBuLi, 2 ^Me underwent deprotonation with subsequent LiCl elimination, 1,2-SiMe₃ migration and Cl/Li exchange to afford the allenyl lithium compound Me₃Si(Li)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiMe₃)₂ (Li[4]), which is an efficient building block for the introduction of Me, SiMe₃, or SnMe₃ (5) groups. The trisilylated, monochlorinated allene Cl₃Si(Cl)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiCl₃)₂ (6), was obtained from [nBu₄N][1] through Cl^--ion abstraction with AlCl₃ and rearrangement in CH₂Cl₂ (1˙ forms as a minor side product, likely because the system AlCl₃/CH₂Cl₂ can also act as a one-electron oxidant).

SUBMITTER: Georg I

PROVIDER: S-EPMC8480423 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:This study shows that methyl 2-aminobenzoate (also known as methyl anthranilate, hereafter MA) undergoes direct photolysis under UVC and UVB irradiation and that its photodegradation is further accelerated in the presence of H₂O₂. Hydrogen peroxide acts as a source of hydroxyl radicals (·OH) under photochemical conditions and yields MA hydroxyderivatives. The trend of MA photodegradation rate vs. H₂O₂ concentration reaches a plateau because of the combined effects of H₂O₂ absorption saturation and ·OH scavenging by H₂O₂. The addition of chloride ions causes scavenging of ·OH, yielding Cl₂·- as the most likely reactive species, and it increases the MA photodegradation rate at high H₂O₂ concentration values. The reaction between Cl₂·- and MA, which has second-order rate constant k C l 2 • - + M A = (4.0 ± 0.3) × 10⁸ M-1·s-1 (determined by laser flash photolysis), appears to be more selective than the ·OH process in the presence of H₂O₂, because Cl₂·- undergoes more limited scavenging by H₂O₂ compared to ·OH. While the addition of carbonate causes ·OH scavenging to produce CO₃·- ( k C O 3 • - + M A = (3.1 ± 0.2) × 10⁸ M-1·s-1), carbonate considerably inhibits the photodegradation of MA. A possible explanation is that the elevated pH values of the carbonate solutions make H₂O₂ to partially occur as HO₂-, which reacts very quickly with either ·OH or CO₃·- to produce O₂·-. The superoxide anion could reduce partially oxidised MA back to the initial substrate, with consequent inhibition of MA photodegradation. Fast MA photodegradation is also observed in the presence of persulphate/UV, which yields SO₄·- that reacts effectively with MA ( k S O 4 • - + M A = (5.6 ± 0.4) × 10⁸ M-1·s-1). Irradiated H₂O₂ is effective in photodegrading MA, but the resulting MA hydroxyderivatives are predicted to be about as toxic as the parent compound for aquatic organisms (most notably, fish and crustaceans).

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The power of trichlorosilylation: isolable trisilylated allyl anions, allyl radicals, and allenyl anions.

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