On A Form with a split container I added a Map Control docked in one panel and a toccontrol docked the other.  I set the mapcontrol to be the buddycontrol of the toccontrol.
and added a mouse down event to that has the following code.  This works perfectly in ArcGIS 10.2.2, the map expands and contracts and changes the extent as expected. Basically what your button would do.  

This functionality works fine out of the box.


        private void axMapControl1_OnMouseDown(object sender, ESRI.ArcGIS.Controls.IMapControlEvents2_OnMouseDownEvent e)
        {
            if (splitContainer1.Panel1Collapsed == true)
            {
                splitContainer1.Panel1Collapsed = false;

            }
            else
                splitContainer1.Panel1Collapsed = true;
        }