Theoretical Description of Base-Stabilized Silylene Complexes

4 Theoretical Description of Base-Stabilized Silylene Complexes 

For a theoretical consideration of the metal-silicon interaction in silylene complexes, the fragment orbital description proves to be very useful [148], This approach has been extensively used in the organometallic chemistry of carbon and allows a basic understanding of the interrelations also by means of a qualitative description. 

The required fragment orbitals for C3y Fe(CO)4 and C4v Cr(CO)5 are taken from the literature, also the orbitals of the respective silylenes (Fig. 8). 

An ab-initio calculation for (OC)5Cr = Si(OH)H shows parallels to the parent carbon compound. However, the electron deficiency at the silicon atom is significantly higher compared to the carbene complex. The LUMO of the Cr=Si 

Since the LUMO is n-antibonding, the kinetically controlled interaction of a donor molecule (HMPA) with the silicon leads to a decrease of multiple bonding between Cr and Si concomitant with a pyramidalization at the silicon atom. The resulting MSi bond distance and pyramidalization effect are strongly influenced by the respective substituents. 

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