So, we're here. To all of you claiming that Minato can be trapped by a genjutsu, please support your claim showing that Minato is weak against genjutsu. Until proven, we can say that Minato can't be trapped by a genjutsu. We'll use Tobi vs Minato as an example. Tobi failed to use genjutsu several times. I was the one who said that he can't be trapped in a genjutsu because this is more logical than saying Tobi DID NOT ATTEMPT TO USE IT. It defeats Tobi's purpose/plan of attacking the village.
Try to ask yourself why didn't he attempt to use genjutsu? Can you find an answer to that? Do you think it is reasonable enough that he rather chose to be defeated by Minato than using genjutsu on MInato. Come on, genjutsu are their advantage over the others. HE was able to use it on kyuubi and yagura. Why not on Minato?
Just look at this way. Tobi's plan was to destroy the village that's why he needed the fox. Minato destroyed his plan. If Tobi was wise enough, he will control Minato and order him to destroy the village alongside kyuubi. If he was able to do this, his plan would definitely be a success.
Isn't it odd why he chose not to use it? Is there a logical reason as to why he didn't use it? If this is the case then it defeats his purpose of destroying the village. It doesn't make sense at all. Just try to ask yourself why he didn't attempt to use it. I bet you can't find an answer to that.