Question

Which complex would you expect to have longer Fe-P bonds, (η⁵-C₅H₅)Fe(Cl)[PMe₃)(CO) or (η⁵-C₅Me₅)Fe(Cl)[PMe₃)(CO)? Explain.

Answer 1

The whole coordination sphere is same just -C₅H₅ has been replaced by -C₅Me₅ in the second complex. Now cyclopentadienyl moiety is e- donor ligand . Changing the substituent of H by Me increases the e- density in the ligand as well as thus in Fe centre also. Now look over the rest of the ligands which are PMe₃ and CO which are e- withdrawing type. In 2nd complex e- density over the metal is higher so e- will be much more attracted by both PMe₃ and CO . Thus increasing the bond order between metal and this ligands. Thus Fe-P bond length will become shorter in 2nd complex.