Is he grabbing her scruff, dragging her, and trying to hump her? If so, even a neutered male sometimes continues this behavior if the female is not spayed. That said, I've seen even neutered males do this to other neutered males in a sexual way, so spaying alone may not stop this behavior. Like any behavior, even an instinctive one, you can train it out in many cases. Some people spray the mounting cat with water (it is more efficient in a case like this if they do not know you are the one spraying them. Teaching that that humping=wet will be more beneficial in this case than people+humping=wet when people are around) and then reward good behavior. Not just punishing, but also rewarding is very important. Then you are reinforcing the behavior you want to see, not just diminishing a behavior or just stopping it when you are around. How long have these cats been together?
If there is mounting and then chasing the female away, the behavior is probably more territorial/hierarchical in nature. In this case, respecting the male's position around the house will probably help matters. This is especially true if this is a newly introduced cat. If so, it usually helps introductions immensely to keep the cats separated except for supervised interaction time, and slowly making an introduction.
I have heard of male cats carrying around both young kittens and adult ferrets by the neck scruff, not in a predatory way, but as a mother would carry her kittens, but never a two year-old cat.
