Palpatine seduced Anakin by promising he could save Padmé using the dark side of the Force. But in the end, he lied that she was killed by Anakin by mistake. Anakin had already turned to the dark side, so she couldn't have been a hurdle. The dark side was powerful enough to save Padmé (think about the virgin birth of Anakin).
So, what was the point behind not keeping his promise?