A THEORETICAL INVESTIGATION OF DONOR-ACCEPTOR BONDING BETWEEN AMINES AND SILYLENES

The dative Si-N bond dissociation enthalpy D0 in SiH2<--NH3 has been estimated as 97 +/- 10 kJ mol-1 at the G2 level of theory. D0 values for substituted analogs and cyclic complexes closed by intramolecular Si-N bonds have been obtained by means of isodesmic reactions, and strains in four-, five-, and six-membered rings are shown to be small. D0 in SiH2-(NH3)2 is estimated to be 7 +/- 20 kJ mol-1. Kinetic implications of D0 are discussed. Vibrational frequencies and UV/visible spectra of various silylenes and silaylides are predicted, to obtain changes in the S0 --> S1 energy relative to SiH2. Ylide formation is seen to increase this gap, and CIS/6-31+G* results suggest that complexation of SiH2 with NH3 shifts the absorption from 485 to 301 nm.