Inter- and Intramolecular Experimental and Calculated Equilibrium Isotope Effects for (silox)₂(ᵗBu₃SiND)TiR + RH (silox = ᵗBu₃SiO): Inferred Kinetic Isotope Effects for RH/D Addition to Transient (silox)₂Ti=NSiᵗBu₃

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This article discusses inter- and intramolecular experimental and calculated equilibrium isotope effects.

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23 p.

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Slaughter, LeGrande M.; Wolczanski, Peter T.; Klinckman, Thomas R. & Cundari, Thomas R., 1964- August 23, 2000.

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This article discusses inter- and intramolecular experimental and calculated equilibrium isotope effects.

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23 p.

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Reprinted with permission from the Journal of the American Chemical Society. Copyright 2000 American Chemical Society.

Abstract: Intermolecular equilibrium isotope effects (EIEs) were measured (26.5 ˚C) and calculated for (silox)₂₋ (ᵗBu₃SiND)TiRᴅ (1-ND-Rᴅ) + RʜH ⇆ (silox)₂(ᵗBu₃SiNH)TiRʜH/RᴅD = CH₄/CD₄, 2.00(6), calcd 1.88; C₂H₆/C₂D₆, 2.22(8), 1.93; ᶜC₃H₆/C₃D₆, 1.71(4), 1.48; C₂H₄/C₂D₄, 1.41(11), 1.34; C₆H₆/C₆D₆, 1.22(7), 1.26; C₇H₈/C₇D₈ (50.0 ˚C), 1.59(6), 1.55. Related intramolecular EIEs for (silox)₂(ᵗBu₃SiND)- TiR' (1-ND-R') ⇆ (silox)₂(ᵗBu₃SiNH)TiR (1-R) are provided: RH = R'D = CH₃D, 3.16(25), calcd 2.60; CH₂D₂, 1.13(8), 0.911; CHD₃, 0.389(20), 0.303; CH₃CD₃, 1.53(3), 1.44; 1, 1-ᶜC₃H₄D₂, 2.58(6), 2.53; trans-HDC=CHD, 1.00(2), 1.00; 1,3,5-C₆H₃D₃, 1.273(4), 1.25; PhCH₂D (50.0 ˚C), 2.06(2), 1.98. Calculations of pertinent model complexes (e.g., (HO)₂(H₂N)TiR (1'R)) generated the vibrational frequencies necessary to interpret the EIEs in terms of a statistical mechanics description utilizing gas-phase partition functions; EIE = SYM x MMI x EXC x EXP[-(∆∆ZPE/kʙT)]. The large MMI term in the intermolecular cases-a consequence of using perprotio vs perdeuterio small molecule substrates-is attenuated by EXC and EXP[-(∆∆ZPE/kʙT)] contributions derived from low-energy core vibrations. The EIEs are differentiated on the basis of the EXP [-(∆∆ZPE/kʙT)] term, with CH-based bending vibrations playing the major role. Substrate bending vibrations that are absent in intramolecular cases are primarily responsible for the greater intermolecular values. Using measured (or calculated) EIEs and kinetic isotope effects for 1,2-RH-elimination (KIEelim) from 1-R, KIEaddn values for 1,2-RH-addition to putative intermediate (silox)₂Ti=NSiᵗBu₃ (2) were inferred via EIE = KIEaddn/KIEelim. Extraordinary intermolecular KIEaddn values ranging from ~ 30(CH₄/CD₄, C₂H₆/C₂D₆) to ~ 9 (C₆H₆/C₆D₆) are consistent with previous mechanistic accounts and may be conventionally rationalized.

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  • Journal of the American Chemical Society, 2000, Washington DC: American Chemical Society, pp. 7953-7975

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  • Publication Title: Journal of the American Chemical Society
  • Volume: 122
  • Issue: 33
  • Page Start: 7953
  • Page End: 7975
  • Peer Reviewed: Yes

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Slaughter, LeGrande M.; Wolczanski, Peter T.; Klinckman, Thomas R. & Cundari, Thomas R., 1964-. Inter- and Intramolecular Experimental and Calculated Equilibrium Isotope Effects for (silox)₂(ᵗBu₃SiND)TiR + RH (silox = ᵗBu₃SiO): Inferred Kinetic Isotope Effects for RH/D Addition to Transient (silox)₂Ti=NSiᵗBu₃, article, August 23, 2000; [Washington, DC]. (digital.library.unt.edu/ark:/67531/metadc107772/: accessed April 28, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.