# Nucleophilicity of bonding vs lone pairs

Does the bonding pair in $\ce{FeCl4^-}$ attack a proton or does a lone pair on the chlorine attack the proton?

My prof has an argument for the first one; the first one involves fewer steps, so it is probably more favorable. My proposed mechanism has three steps of electron pushing versus two, so okay.

However, I can see an argument for the second mechanism - the first one involves a bonding pair acting as a nucleophile rather than a lone pair on chlorine. The bonding pair is stabilized by the chlorine and the iron atom, while the lone pair is stabilized by only the chlorine.

So, which one wins? I'm guessing both mechanisms are operative here.