That's exactly what a motor speed control inverter does, it lowers the frequency to reduce the speed.
The problem is your motor isn't designed to be operated from a lower frequency than 50Hz. Because the impedance of an inductor is directly proportional to the frequency more current will flow causing it to overheat. It might be possible to use a modified sine wave to keep the current down but there might be issues with harmonics and the motor's phase shifting mechinism not working at the lower frequency.
Normal AC motors won't work from a single phase mains supply, they require a rotating magnetic field to work, otherwise how do the magnets know which way to turn? To get round this problem all sorts of techniques are used, like a run capacitor or shaded pole, the idea is to provide a phase shift and a rotating field. The problem is often these techniques are highly frequency dependant, for example at a lower frequency a start capacitor will have a much lower phase shift which might not be enough to start the motor