[I_complete_me]

Slight correction: m-dash `Ctrl+k -M` or, for n-dash `Ctrl+k -N`.

What also works (though more cumbersome) are:

For m-dash: Ctrl+q u2014 and for n-dash: Ctrl+q u2013

My vim set up requires Ctrl+q but probably it's normally Ctrl+v, may need to check.