This is because the lone pair of electron of `N` (present in the2p orbital ) is transferred to the empty d-orbital of Si (`ppi-dpi` overlapping) and hence it is not available for protonation . As a result, `N(SiMe_(3))_(3)` is a weaker base than `N(CH_(3))_(3)` or `N(SiH_(3))_(3)` is a stronger base than `N(CH_(3))_(3)`.
