Silicon Effects. III. Rates and Products for Solvolysis of .ALPHA.-(Pentamethyldisilanyl)benzyl Halides and 1,1,2,2-Tetramethyl-1,2-disilaindan-3-yl Chloride. Structure and Stability of .ALPHA.-(Pentamethyldisilanyl)benzyl Cation in Solution.

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概要

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• Detailed kinetic and product studies have been made on solvolysis of α-(pentamethyldisilanyl)benzyl halides (<B>1a-X</B>; X=Cl and Br) and 1,1,2,2-tetramethyl-1,2-disilaindan-3-yl chloride (<B>2</B>-Cl) in various solvents. The solvolysis of <B>1a-X</B> at 25°C is characterized by (1) a complete 1,2-SiMe<SUB>3</SUB> rearrangement in the products, (2) <I>m</I> (sensitivity to the solvent ionizing power <I>Y</I><SUB>x</SUB>) values of 0.98 (X=Cl) and 0.91 (X=Br) for the solvolyses in aq acetone, (3) α-deuterium isotope effects of 1.167 and 1.163 for <B>1a-Cl</B> in 97% aq 2,2,2-trifluoroethanol (TFE) and 40% aq ethanol respectively, and (4) substituent effect expressed by a Yukawa–Tsuno LArSR equation: log<I>k</I>⁄<I>k</I><SUP>H</SUP>=−3.71 (σ<SUP>°</SUP>+1.16 Δ\barσ<SUB>R</SUB><SUP>+</SUP>) for the solvolysis of <B>1a-Cl</B> and the <I>p</I>-Me, <I>m</I>-Me, <I>p</I>-Cl, and <I>m</I>-Cl derivatives in 40% aq ethanol. These findings are consistent with <I>k</I><SUB>c</SUB> mechanism. The relative rates for <B>1a-Br</B>, α-(trimethylsilyl)benzyl bromide, and α-(<I>t</I>-butyldimethylsilyl)benzyl bromide are 1.07×10<SUP>5</SUP> : 0.54 : 1.0 in 97% aq TFE at 25°C indicating solvolytic generation of α-(pentamethyldisilanyl)benzyl cation to be ca. 7 kcal mol<SUP>−1</SUP> energetically more favorable than that of the corresponding α-(trialkylsilyl)benzyl cations. In contrast, <B>2-Cl</B> solvolyzes 0.209 times less rapidly than does 2,2-dimethyl-2-silaindan-l-yl chloride in 97% aq TFE indicating that a β-Si-Si σ bond orthogonal to the leaving group does not enhance the rate of ionization at all.

• 公益社団法人 日本化学会の論文

著者

• Tsuno Yuho

  Department Of Chemistry Faculty Of General Education Kumamoto University

• Shimizu Nobujiro

  Department Of Chemistry Faculty Of Science Kyushu University

• Osajima Erika

  Department of Chemistry, Faculty of Science, Kyushu University

• Kinoshita Chieko

  Department of Chemistry, Faculty of Science, Kyushu University

• Hayakawa Fumie

  Department of Chemistry, Faculty of Science, Kyushu University

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