I was reading in The Organometallic Chemistry of the Transition Metals (Robert Crabtree) that lewis acids like BF3 often accept electrons from d(pi) orbitals. Is this generally true for all pi acceptor ligands? That is, do metals with filled d(pi) orbitals form thermodynamically stable bonds with pi acceptor ligands? I would imagine that d(pi) electrons would only be available for donation if said metal was in a low oxidation state. Correct me if I'm wrong.

If this post merits two different question threads, I'd be happy to separate them.