Not sure what rights of last refusal are but I've heard of rights of first refusal. Basically the same thing I guess in that the "refusal" right seems to indicate that the holder would get to match any other higher bid whereas the "negotiation" right could not guarantee such and could be bypassed by a competitor. Certainly not a business expert though.
(1)
(1)
Innovation Pharmaceuticals Inc (IPIX) Stock Research Links