"Front Matter". In: Organosilanes in Radical Chemistry - Index of
"Front Matter". In: Organosilanes in Radical Chemistry - Index of "Front Matter". In: Organosilanes in Radical Chemistry - Index of
Structural Properties of Silyl Radicals 15 according to electronegativity. The calculated angles g (see structure 19) for the silyl radicals with different substituents (in parentheses) are: 17.738 (H), 18.698 (CH3), 21.53 8 (NH2), 20.76 8 (OH), 20.77 8 (F), 13.40 8 (SiH3), 22.68 8 (PH2), 20.51 8 (SH), and 19.43 8 (Cl). Therefore, for all these trisubstituted radicals, the arrangement of atoms around the silicon is found to be essentially tetrahedral with the exception of the (H3Si) 3Si: radical which is much less bent. The magnitude and the trend of the 29 Si hfs constants from EPR spectra are well reproduced by these calculations and are due to more 3s character of the unpaired electron orbital at the Si-center rather than to a general change of geometry at radical centre. The calculations show that in the SOMO the delocalization of the unpaired electron onto the a-substituent increases from second to third row elements, whereas the population on Si-3s increases linearly with the increasing electronegativity of the a-substituent. For example, the calculated distribution of the unpaired electron density for Me3Si: is 81 % on silicon (14.3 % in 3s, 64.6 % in 3p, and 2.1 % in 3d) and 19 % on methyls; for F3Si: it is 84.4 % on silicon (41.8 % in 3s, 32.6 % in 3p, and 6.4 % in 3d) and 15.6 % on fluorines; for Cl3Si: it is 57.3 % on silicon (21.5 % in 3s, 32.6 % in 3p, and 3.2 % in 3d) and 42.7 % on chlorines. UMP2/DZP/TZP calculations have been extended to the series H3 nSi(:)Men(n ¼ 0–2) addressing the early controversy about the signs of a- 1 H hfs constants [34]. The sign was found to be positive for all these radicals, which have a nearly tetrahedral geometry at silicon. The same level of theory has been used to calculate the a- 29 Si hfs constants of series Me3 nSi(:)Cln and Me3 nSi(:)(SiMe3) n(n ¼ 0–3) and to analyse observed trends [60]. The large increase of the 29 Si hfs when Me is successively replaced by Cl is mainly due to the change of the Si orbital populations rather than to structural changes, whereas when Me is replaced by SiMe3 the considerable decrease is due to the increased spin delocalization and the flatter geometry. The structural parameters of (HS) 3Si: radicals were computed at the HF/6- 31G* level for C3 symmetry [58]. The radical centre at silicon is pyramidal. Two minima have been found along the energy surface generated by the synchronous rotation of the SH groups. In the most stable conformation 20, the hydrogens adopt a gauche conformation (v ¼ 50 ) with respect to the SOMO, which is mainly the sp 3 atomic orbital (AO) of Si. In the other minimum 21, which is 18.4 kJ/mol higher in energy, the hydrogens are nearly anti (v ¼ 150 ) with respect to the SOMO. HS 20 ω H SH Multiple scattering Xa (MSXa) method was applied to assign the optical absorption spectra of Me3Si: and (MeS) 3Si: radicals. The strong band HS 21 H SH
16 Formation and Structures of Silyl Radicals observed for (alkyl) 3Si: radicals at ca 260 nm has been attributed to the superimposition of the valence transition from the MO localized at the Si w C bond to the SOMO and of the transition from the SOMO to the 4p Rydberg orbital [61]. Furthermore the observed weak band between 350 and 450 nm for Et3Si: radical (Figure 1.4) has been assigned to the transition from SOMO to the 4s Rydberg orbital. For the (MeS) 3Si: radical [58], the strong band has been attributed to transitions from the SOMO (localized mainly at the 3p AO of Si) to the antibonding s Si S MOs (a1 and e symmetry). A contribution to the intensity of this band could also derive from the valence transition from the sSi S(a1) MO to the SOMO and from the Rydberg transition from the SOMO to the 4p(a 1) orbital. The weak band/shoulder at ca 425 nm has been assigned to the valence excitation from the MO localized at the Si w S bond to the SOMO. Transitions from sulfur lone pairs to the SOMO have much lower oscillator strengths and are predicted to occur in the near-infrared region. 1.3 REFERENCES 1. Chatgilialoglu, C., Chem. Rev., 1995, 95, 1229. 2. Chatgilialoglu, C., and Newcomb, M., Adv. Organomet. Chem., 1999, 44, 67. 3. Steinmetz, M.G., Chem. Rev., 1995, 95, 1527. 4. Leigh, W.J., and Sluggett, G.W., J. Am. Chem. Soc., 1993, 115, 7531. 5. Leigh, W.J., and Sluggett, G.W., Organometallics, 1994, 13, 269. 6. Sluggett, G.W., and Leigh, W.J., Organometallics, 1994, 13, 1005. 7. Sluggett, G.W., and Leigh, W.J., Organometallics, 1992, 11, 3731. 8. McKinley, A.J., Karatsu, T., Wallraff, G.M., Thompson, D.P., Miller, R.D., and Michl, J., J. Am. Chem. Soc., 1991, 113, 2003. 9. Davidson, I.M.T., Michl, J., and Simpson, T., Organometallics, 1991, 10, 842. 10. Matsumoto, A., and Ito, Y., J. Org. Chem., 2000, 65, 5707. 11. Tamao, K., and Kawachi, A., Adv. Organomet. Chem., 1995, 38, 1. 12. Kira, M., Obata, T., Kon, I., Hashimoto, H., Ichinohe, M., Sakurai, H., Kyushin, S., and Matsumoto, H., Chem Lett., 1998, 1097. 13. Sekiguchi, A., Fukawa, T., Nakamoto, M., Lee, V. Ya., and Ichinohe, M., J. Am. Chem. Soc., 2002, 124, 9865. 14. Shizuka, H., and Hiratsuka, H., Res. Chem. Intermed., 1992, 18, 131. 15. Kako, M., and Nakadaira, Y., Coord. Chem. Rev., 1998, 176, 87. 16. Pandey, G., and Rao, K.S.S.P., Angew. Chem. Int. Ed. Engl., 1995, 34, 2669. 17. Pandey, G., Rao, K.S.S.P., Palit, D.K., and Mittal, J.P., J. Org. Chem., 1998, 63, 3968. 18. Pandey, G., Rao, K.S.S.P., and Rao, K.V.N., J. Org. Chem., 2000, 65, 4309. 19. Nishiyama, Y., Kajimoto, H., Kotani, K., and Sonoda, N., Org. Lett., 2001, 3, 3087. 20. Nishiyama, Y., Kajimoto, H., Kotani, K., Nishida, T., and Sonoda, N., J. Org. Chem., 2002, 67, 5696. 21. Symons, M.C.R., Chemical and Biochemical Aspects of Electron-Spin Resonance Spectroscopy, Van Nostrand Reinhold, Melbourne, 1978. 22. Sommer, L.H., and Ulland, L.A., J. Org. Chem., 1972, 37, 3878. 23. Chatgilialoglu, C., Ingold, K.U., and Scaiano, J.C., J. Am. Chem. Soc., 1982, 104, 5123. 24. Sakurai, H., and Murakami, M., Bull. Chem. Soc. Jpn., 1977, 50, 3384.
- Page 1 and 2: Organosilanes in Radical Chemistry
- Page 3 and 4: DEDICATION To my parents XrZstoB an
- Page 5 and 6: viii Contents 3.6 Hydrogen Atom: An
- Page 7 and 8: PREFACE A large number of papers de
- Page 9 and 10: ACKNOWLEDGEMENTS I thank Keith U. I
- Page 11 and 12: 2 Formation and Structures of Silyl
- Page 13 and 14: 4 Formation and Structures of Silyl
- Page 15 and 16: 6 Formation and Structures of Silyl
- Page 17 and 18: 8 Formation and Structures of Silyl
- Page 19 and 20: 10 Formation and Structures of Sily
- Page 21 and 22: 12 Formation and Structures of Sily
- Page 23: 14 Formation and Structures of Sily
- Page 27 and 28: 2 Thermochemistry 2.1 GENERAL CONSI
- Page 29 and 30: Bond Dissociation Enthalpies 21 Tab
- Page 31 and 32: Bond Dissociation Enthalpies 23 2.2
- Page 33 and 34: Ion Thermochemistry 25 Table 2.4 Re
- Page 35 and 36: Ion Thermochemistry 27 Table 2.5 El
- Page 37 and 38: References 29 3. Goumri, A., Yuan,
- Page 39 and 40: 32 Hydrogen Donor Abilities of Sili
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- Page 45 and 46: 38 Hydrogen Donor Abilities of Sili
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- Page 55 and 56: 4 Reducing Agents 4.1 GENERAL ASPEC
- Page 57 and 58: General Aspects of Radical Chain Re
- Page 59 and 60: Tris(trimethylsilyl)silane 53 Therm
- Page 61 and 62: Tris(trimethylsilyl)silane 55 4.3.1
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- Page 71 and 72: Tris(trimethylsilyl)silane 65 RO RO
- Page 73 and 74: Tris(trimethylsilyl)silane 67 O AcO
16 Formation and Structures <strong>of</strong> Silyl <strong>Radical</strong>s<br />
observed for (alkyl) 3Si: radicals at ca 260 nm has been attributed to the<br />
superimposition <strong>of</strong> the valence transition from the MO localized at the Si w C<br />
bond to the SOMO and <strong>of</strong> the transition from the SOMO to the 4p Rydberg<br />
orbital [61]. Furthermore the observed weak band between 350 and 450 nm for<br />
Et3Si: radical (Figure 1.4) has been assigned to the transition from SOMO to<br />
the 4s Rydberg orbital. For the (MeS) 3Si: radical [58], the strong band has been<br />
attributed to transitions from the SOMO (localized ma<strong>in</strong>ly at the 3p AO <strong>of</strong> Si)<br />
to the antibond<strong>in</strong>g s Si S MOs (a1 and e symmetry). A contribution to the<br />
<strong>in</strong>tensity <strong>of</strong> this band could also derive from the valence transition from the<br />
sSi S(a1) MO to the SOMO and from the Rydberg transition from the SOMO<br />
to the 4p(a 1) orbital. The weak band/shoulder at ca 425 nm has been assigned to<br />
the valence excitation from the MO localized at the Si w S bond to the SOMO.<br />
Transitions from sulfur lone pairs to the SOMO have much lower oscillator<br />
strengths and are predicted to occur <strong>in</strong> the near-<strong>in</strong>frared region.<br />
1.3 REFERENCES<br />
1. Chatgilialoglu, C., Chem. Rev., 1995, 95, 1229.<br />
2. Chatgilialoglu, C., and Newcomb, M., Adv. Organomet. Chem., 1999, 44, 67.<br />
3. Ste<strong>in</strong>metz, M.G., Chem. Rev., 1995, 95, 1527.<br />
4. Leigh, W.J., and Sluggett, G.W., J. Am. Chem. Soc., 1993, 115, 7531.<br />
5. Leigh, W.J., and Sluggett, G.W., Organometallics, 1994, 13, 269.<br />
6. Sluggett, G.W., and Leigh, W.J., Organometallics, 1994, 13, 1005.<br />
7. Sluggett, G.W., and Leigh, W.J., Organometallics, 1992, 11, 3731.<br />
8. McK<strong>in</strong>ley, A.J., Karatsu, T., Wallraff, G.M., Thompson, D.P., Miller, R.D., and<br />
Michl, J., J. Am. Chem. Soc., 1991, 113, 2003.<br />
9. Davidson, I.M.T., Michl, J., and Simpson, T., Organometallics, 1991, 10, 842.<br />
10. Matsumoto, A., and Ito, Y., J. Org. Chem., 2000, 65, 5707.<br />
11. Tamao, K., and Kawachi, A., Adv. Organomet. Chem., 1995, 38, 1.<br />
12. Kira, M., Obata, T., Kon, I., Hashimoto, H., Ich<strong>in</strong>ohe, M., Sakurai, H., Kyush<strong>in</strong>, S.,<br />
and Matsumoto, H., Chem Lett., 1998, 1097.<br />
13. Sekiguchi, A., Fukawa, T., Nakamoto, M., Lee, V. Ya., and Ich<strong>in</strong>ohe, M., J. Am.<br />
Chem. Soc., 2002, 124, 9865.<br />
14. Shizuka, H., and Hiratsuka, H., Res. Chem. <strong>In</strong>termed., 1992, 18, 131.<br />
15. Kako, M., and Nakadaira, Y., Coord. Chem. Rev., 1998, 176, 87.<br />
16. Pandey, G., and Rao, K.S.S.P., Angew. Chem. <strong>In</strong>t. Ed. Engl., 1995, 34, 2669.<br />
17. Pandey, G., Rao, K.S.S.P., Palit, D.K., and Mittal, J.P., J. Org. Chem., 1998, 63,<br />
3968.<br />
18. Pandey, G., Rao, K.S.S.P., and Rao, K.V.N., J. Org. Chem., 2000, 65, 4309.<br />
19. Nishiyama, Y., Kajimoto, H., Kotani, K., and Sonoda, N., Org. Lett., 2001, 3, 3087.<br />
20. Nishiyama, Y., Kajimoto, H., Kotani, K., Nishida, T., and Sonoda, N., J. Org.<br />
Chem., 2002, 67, 5696.<br />
21. Symons, M.C.R., Chemical and Biochemical Aspects <strong>of</strong> Electron-Sp<strong>in</strong> Resonance<br />
Spectroscopy, Van Nostrand Re<strong>in</strong>hold, Melbourne, 1978.<br />
22. Sommer, L.H., and Ulland, L.A., J. Org. Chem., 1972, 37, 3878.<br />
23. Chatgilialoglu, C., <strong>In</strong>gold, K.U., and Scaiano, J.C., J. Am. Chem. Soc., 1982, 104,<br />
5123.<br />
24. Sakurai, H., and Murakami, M., Bull. Chem. Soc. Jpn., 1977, 50, 3384.
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