UPDATE: Deal is done according to a Bruce Levine tweet, don't know the name of the minor leaguers yet and the players must pass physicals.
ESPN Chicago and Fox Sports both reported last night that the Cubs were close on a deal to send the "best left-handed reliever in baseball" to the Cincinnati Reds, possibly for left-handed starter Travis Wood and 2 more minor leaguers. It seems the "2 more" will be the key to deal. And of course, nothing is official yet with plenty of water already thrown on this rumor fire. But it may happen, and if so, let's see why it might make some sense.
Under the new CBA, relievers will almost certainly not being getting their old club free agent compensation and Marshall was set to be one after 2012. Better to get something now than nothing later with 2012 looking like a non-competitive season for the Cubs. Also, it's generally a good idea to trade a reliever for a starter, at least a starter that won't be a free agent until after 2016 and you probably expect to be average or slightly better. Wood will be just 25 next season after all. And as mentioned, there seems to be talk of at least 2 other Reds coming over and we'll have to see who those are.