Bootstrap Dropdown Button with Block Level?

I'm trying to make a bootstrap 3 dropdown button accept the full width (.btn-block class) properties. It doesn't seem to work the same way with the drop down button as it does with regular buttons. Here is my current code:

<div class="row">
  <div class="col-md-6 col-sm-6 col-xs-6">
    <!-- Single button -->
    <div class="btn-group">
      <button type="button" class="btn btn-primary btn-block dropdown-toggle" data-toggle="dropdown">
        <span class="glyphicon glyphicon-cog"></span> Dealer Tools  <span class="caret"></span>
      </button>
      <ul class="dropdown-menu" role="menu">
         <li><a href="#"><span class="glyphicon glyphicon-user"></span> Dealer Area</a></li>
         <li class="divider"></li>
         <li><a href="#"><span class="glyphicon glyphicon-phone"></span> App Registration</a></li>   
      </ul>
    </div>
    <!-- Single button -->
  </div>
  <div class="col-md-6 col-sm-6 col-xs-6">
    <a href="http://www.agrigro.com/testarea/contact-us/">
      <button type="button" class="btn btn-primary btn-block">
        <span class="glyphicon glyphicon-envelope"></span>  CONTACT US
      </button>
    </a>
  </div>
</div>

How can I get this to work right so the dropdown button takes up the full col-6?