Simple array question

the below code works:
var buttonArray:Array = new Array (button1, button2, button3, button4, button5);
for (var i = 0; i < buttonArray.length; i++) {
buttonArray*.onRelease = function () {
this._x += 5;
};
}
but this doesn’t:
var buttonArray:Array = new Array (button1, button2, button3, button4, button5);
for (var i = 0; i < buttonArray.length; i++) {
buttonArray*.onRelease = function () {
this.onEnterFrame=function(){
this._x += 5;
}
};
}

Why won’t the onEnterFrame work?