Organometallics  17  (1998) 2352-2360
Probing Delocalization in Stable Silylenes: Core Excitation Spectra of Si(NRCH=CHNR),
Si(NRCH2CH2NR), H2Si(NRCH=CHNR), and H2Si(NRCH2CH2NR) (R = tBu)
Stephen G. Urquhart,, Adam P, Hitchcock,*, John F. Lehmann, and Michael Denk§
Department of Chemistry, McMaster University, Hamilton, Ontario, Canada, L8S 4MI
§Department of Chemistry, University of Toronto, Mississauga, Ontario, Canada L5L lC6
Received October 21, 1997
The silicon ls, 2p, and 2s, carbon ls, and nitrogen ls gas-phase core excitation spectra are reported for two stable divalent silylenes, Si(NRCH =CHNR) and Si(NRCH2CH2NR) (R = tBu), and for the two analogous  tetravalent  dihydridosilane molecules, H2Si(NRCH=CHNR) and H2Si(NRCH2CH2NR) (R = tBu).  The nature of the excited states arising from one electron core®p* and core®s* excitations at different sites on the silylene ring are examined by relating the changes in the spectra of these compounds to differences in their molecular structure.  The variations in the intensities of core®p* transitions in these spectra probe the extent of delocalization in the p-electron manifold and, thus, allow us to investigate the nature of p stabilization in heterocycles containing divalent silicon.  Low-lying transitions to a p*(Si-N) lever observed in all core edge spectra strongly support the existence of p-delocalization in the C=C unsaturated silylene. Ab initio calculations are used to confirm spectral assignments.

©1998 American Chemical Society