Alfonso Soriano, who has a no-trade clause, reportedly would not have allowed a trade to the Pirates, although it's not clear whether the Pirates were in discussions to get him.
UPDATE: I'm not sure I totally get the sentiment in the comments. Soriano isn't a bad player. He's just massively overpaid. I agree it isn't likely, but if the Cubs had been willing to eat a ton of salary, I don't see why acquiring him would have been a bad move.