Create 2D box colliders based on current frame of animation

I'm working on a 2D side-scrolling RPG. I'm looking for ideas on how to set the player's collision boxes based on the animation. For example, if the player is entering a punch combo, I need to create a 2D collider that is only enabled during the frames of the animation when his arm is extended. I'm trying to sync the 2D colliders with the mecanim system.