Bind key combo to a mouse button

I would like to bind a key combination Ctrl+1 to a mouse button. Here is how I tried to do it with xbindkeys:

Code:"xte 'keydown Control_L' 'key 1' 'keyup Control_L'"
b:9This doesn't work as expected however. I'm confused because this works:

Code:"xte 'keydown Control_L' 'key C' 'keyup Control_L'"
b:9I get the Ctrl+C shortcut working correctly.

Am I doing something wrong?