Below is just a Sample Code Snippet.
You need to bind your isFocused Property of your ContentPane to isEnabled Proeperty of ToolbarItem.
By this was,
If ContentPane is Focused then ToolbarItem will be enabled.
<stackpanel>
<contentpane x:name="contentPane" content="Toggle" xmlns:x="#unknown" />
<toolbaritem>
isEnabled"{Binding isFocused , ElementName=contentPane/>
</toolbaritem></stackpanel>