I'm not sure if this is a bug or is intended, but in a current game I have, the AI demanded more money than I had on hand. I could accept and give it to him, which sent me into the negative.
I think this is a bug, but if it's not, this makes no sense. I can't really fork over money I don't have unless I am to assume that my faction has advanced banking securities and whatnot. Especially since the player can't ask for more money from the AI, so I cant then extort my enemies, since you could potentially force them to go negative, setting them back and preventing them from building more units.