I am assuming that when you are trying to catch him he is running around with his tail stuck up but as soon as you get ahold then he is fine and walks with you the barn- then it is just a game to him. It this is the case then you need to reverse it.
If you walk out to catch him and he walks away from keep walking to his head. As soon as he stops and looks at you turn your back to him and ignore him. When he walks off walk to his head and when he stops repeat. You are taking the pressure away when he does what you want, stopping and looking at you. After you catch him I would probably turn him loose again, walk away and try again. if you keep bribing with with grain, soon he will be a grain snatcher and just run off when you go to stick the lead rope over his neck.
As far as the bucking, has he been started by someone else and you bought him or did you start him? All I can say about that is without having a better idea is, there is no sense in throwing your leg all the way over on one if he isn't ok with you being on one side. When starting my colts and getting on for the first time I get their head bent around stand in the stirrup with just my toe and "sack" them out with my other leg. I take my right leg and rub all over their hindquarters rub on their neck with my hand. Don't sneek rides on colts all they end up doing is getting you later. Then I do the same on the other side. Until he is fine with me doing that from both sides do I swing my leg all the way over. Then I get off and on, off and on. Don't ask him to step off yet until he's ok with it. When you do ask him to step off, don't step off straight, always ask for a direction with your rein first.
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.