According to the official twitter of To Love-ru anime, the anime project of To Love-ru Darkness is "thought to be" a false information. Mainichi removed the sentence from the article.
@takaderu_07: I heard To Love-ru Darkness will get an anime adaptation. Is it true?
@toloveru_com: I've also heard of the information, but it looks like a false info. Oh, dear! What should I say. lol
Source: To Love-ru official twitter
According to Mainichi Digital News, an anime project of manga To LOVE-Ru Darkness
has been underway. It's a spin-off of To LOVE-Ru
featuring Golden Darkness and Momo.