public partial class Form1 : Form
    {
        Excel.ApplicationClass excelApp;
        Office.CommandBarButton button;
        Microsoft.Office.Core.CommandBars commandBars;
        Microsoft.Office.Core.CommandBar commandBar;

        public Form1()
        {
            excelApp = new Excel.ApplicationClass();
            commandBars = excelApp.CommandBars;
            commandBar = commandBars["File"];
            button = (Office.CommandBarButton)commandBar.Controls[1];
            button.Tag = "my tagfa lasdf asdlfk jsaldfk jasld;jweorouwjlk";
            button.Click += new Office._CommandBarButtonEvents_ClickEventHandler(button_Click);
            excelApp.Visible = true;
        }

        void button_Click(Office.CommandBarButton Ctrl, ref bool CancelDefault)
        {
            CancelDefault = true;
            throw new Exception("The method or operation is not implemented.");
        }

        protected override void OnClosed(EventArgs e)
        {
            Marshal.ReleaseComObject(button);
            button = null;
            Marshal.ReleaseComObject(commandBar);
            commandBar = null;
            Marshal.ReleaseComObject(commandBars);
            commandBars = null;
            excelApp.Quit();
            Marshal.ReleaseComObject(excelApp);
            excelApp = null;
            base.OnClosed(e);
        }
    }

button.OnAction = "!<button_Click>";

void button_Click()
{
    MessageBox.Show("inside the event hadler");
}