Your problem is that you can't bind to a View-level event from a view-model. That breaks the no-visual-dependency rule for the view model. So you have to covert the routed event into a command.
The most common way to work around this is to use the EventToCommand class in the MVVMLight toolkit. It is the easiest way to do it. However, there is a similar function in the Blend libraries if you don't want to use MVVMLight. It is in the Interactivity namespace. This link should help: http://blogs.msdn.com/b/luc/archive/2010/11/18/executing-a-command-from-an-event-of-your-choice.aspx
Either way you will get the same result.