Class Summary 11/12/04

11/12 More on Strain (Anti-Bredt systems)

Computational studies have shown that systems with carbenes sometimes prefer insertion resulting in Anti-Bredt systems as opposed to leaving the carbenes isolated (Hadad, 2000)

These systems (and related species) studied by Borden et al.

If n=3 (Meier, 1993) (and also substituted by MsO ligands), IR indicates C=C at 1615 cm^-1, UV = 217 ± 5 nm. Compare this to the strain-free system (no bridging methylenes), IR is 1675-1685 cm^-1 and UV is <200 nm.

If n=2 (Michl, 1986), IR shows 1557 cm^-1 and UV = 245 nm. Indicates (a) more pyramidization and (b) C=C interaction is weakening.

If n=1(Michl, 1993, JACS, 1454), IR shows 1496 cm^-1. No UV though.

If n=0, this species has been “trapped”, but not characterized.

Also mentioned, “Olefin Strain Energy” of cubane (Kass).

PAPERS MENTIONED

Geise, C.M. and Hadad, C.M. Formation of Anti-Bredt Olefins from Bridgehead Carbene Precursors: A Computational Study J. Am. Chem. Soc. (2000) 122, 5861 – 5865.

Smith, J.M., Hrovat, D.A., Borden, W.T., Allan, M., Asmis, K.R., Bulliard, C., Haselbach, E., and Meier, U.C. Synthesis and spectroscopy of tricyclo[3.3.3.03,7]undec-3(7)-ene: confirmation of computational predictions regarding the effects of pyramidalization on alkene ionization energies and electron affinities J. Am. Chem. Soc. (1993) 115, 3816-3817.

Radziszewski, J.G., Yin, T.K., Renzoni, G.E., Hrovat, D.A., Borden, W.T., and Michl, J. Matrix isolation of tricyclo[3.3.1.03,7]non-3(7)-ene, a doubly pyramidazlized alkene predicted to have a nearly tetrahedral geometry at the olefinic carbons J. Am. Chem. Soc. (1993) 115, 1454-1456.

Radziszewski, J.G., Yin, T.K., Miyake, F., Renzoni, G.E., Borden, W.T., and Michl, J. A doubly pyramidalized olefin. Matrix isolation spectroscopy of tricyclo[3.3.2.03,7]dec-3(7)-ene J. Am. Chem. Soc. (1986) 108, 3544-3545.

Staneke, P.O., Ingemann, S., Eaton, P., Nibbering, N.M.M., and Kass, S.R. Formation of the Radical Anion of Cubene and Determination of the Heat of Formation, Heat of Hydrogenation, and Olefin Strain Energy of Cubene J. Am. Chem. Soc. (1994) 116, 6445-6446.

Hare, M., Emrick, T., Eaton, P.E., and Kass, S.R. Cubyl Anion Formation and an Experimental Determination of the Acidity and C-H Bond Dissociation Energy of Cubane J. Am. Chem. Soc. (1997) 119, 237-238.

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