Consider that a wolf is about 3-4x bigger than a Coyote. Use your Deer/Big-Game rifle, not your varmint rifle. I would say 243 minimum (90gr or more, not a varmint bullet). You dont want to just barely kill it with a marginal cartridge. You want that thing DEAD
If you're set on an AR15, I would say 6.5 Grendel or 6.8 SPC. Maybe 300 blackout. Would not mess with anything smaller.
(AR10 in .260 Rem would be the shizzy)