it has been my experience that at this age, a child cannot just calm down. My girl is now 6 1/2 and she still has issues with being able to calm down when she gets upset like this.Granted, she is so much better now compared to then, but she is still young, and doestn have total control over her emotins the way a child older than her has. The best thing to do when your son is acting this way is ignore him, and not discuss his issue further until he calms himself down. Go into another room, away from him, let him have his tantrum, and when he is calm, explain the punishment you have settled on, and more importantly, review with him WHY he is in trouble inthe first place. Children at 4 1/2 have very short attention spans, and quickly lose sight of why they are in trouble. Sit down with him and say "What did you do that got you in trouble? Why was that bad? This is why I don't want you to behave that way." And then give him his punishment.
If he continues to try and hurt you, you need to constrain him. wrap your arms around his arms while he is tryin to hit, and sit down with him. You dont want to hurt him, just keep him from hurting himself or you.
I would also suggest your boyfriend and you sit down together, adn make up a good behavior chart for your boy. Every time he behaves well, he gets a sticker. When he gets a certain amount of stickers, he can have a prize. This seems to work well.
goodluck.
liz