Which of the following carbonyls will have the strongest C - O bond?
Fe(CO)5
CO is a pi acceptor ligand, it accepts electron cloud density from metal centre resulting in synergistic effect which called M→L charge transfer. Stronger the M→CO bond weaker the CO bond strength.
Since the manganese complex has a positive metal centre, it is reluctant to give away the electron. As a result, the M→CO bond in the mangnese complex is the weakest.
Hence Mn complex has the strongest C=O bond.