A Rottweiler has a powerful jaw and strong grip, but it is unlikely to defeat a black bear. Black bears can weigh up to 600 pounds and have powerful claws and teeth. A Rottweiler would be at a significant disadvantage.
Black bears are wild animals, unafraid of humans, and can be aggressive toward dogs. If a Rottweiler encountered a black bear, the bear would likely attack the dog. For these reasons, it is not advisable to allow a Rottweiler to come into contact with a black bear.