Question

Why transition element in low oxidation state form complex with weak legands?

Answer 1

Because they are strong sigma donors and pi acceptors, these strong field ligands can stabilize metal ions in low oxidation state.

Answer 2

Why do transition elements in zero, and lower oxidation states ... Formation of complexes by transition element in zero oxidation states is supported by synergic bond .The metal -carbon bond in metal carbonyl possess both s and p character .The M-C sigma bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant orbital of the metal .