Structure-Function Relationships with the Ligand

Ligands other than the departing carbon monoxide will influence the rates of substitution reactions. Good electron donating ligands such as amines and phosphines speed dissociative substitution reactions, because they compensate for the loss of electrons on the metal that occurs in the rate-determining step. This is an important factor to consider when one wants to increase the rate of ligand loss in a catalytic cycle. 

The CO ligands that most rapidly exchange are those that are cis to the donating group (Eq. 12.14). This is because the donating ligands increase the extent of back-bonding mostly 

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