Question

Why pi acid ligands forms complexes with transition metal?

Answer 1

Answer:

The ligand is thus acting as a σ-donor and a π-acceptor. In π-backbonding, the metal donates π electrons to the ligand π* orbital, adding electron density to an antibonding molecular orbital.

Explanation:

This is a common situation for phosphine complexes (e.g., triphenylphosphine) bound to low-valent, late transition metals.