"Dying, Danzō staggered towards Sasuke and Tobi, thinking about Hiruzen and how, no matter what he did, he could never match him, not even having properly become Hokage. With his last breath he proclaimed that for the sake of the world and the safety of Konoha, he would take Sasuke and Tobi with him to the grave. He then activated the Reverse Four Symbols Sealing Technique, but Sasuke and Tobi are able to get out of range. Danzō is nevertheless able to destroy Shisui's Sharingan in order to to prevent Tobi from obtaining it." got from the naruto wiki