yes caliburn is right guysBecause he can't. He can't throw his Rasenshuriken either, only if he's in Sage Mode and even then it's a small miracle as Ma was surprised he could throw such dense-spinning chakra.
Maybe it's possible he can throw it in Sage Mode, but I doubt it. Rasenshuriken is a wind-type jutsu + it pretty much has the form ideal for a throwing object, if a Rasengan would be thrown, it would just disappear.
Thats because that type of rasengan is held in a Shuriken like chakra...When Naruto creates and throws the Rasen-shurikan, the Rasengan stilll holds it's shape. I still think he should be able to throw the Rasengan.