Oxidative Addition
• We have seen how neutral ligands such as C2H4 or CO can enter the coordination sphere of a
metal by substitution. We now look at a general method for simultaneously introducing pairs of
anionic ligands, A and B, by the oxidative addition of an A−B molecule such as H2 or CH3‐I.
• The reverse reaction, reductive elimination, leads to the extrusion of A−B from an M(A)(B)
complex and is often the product‐forming step in a catalytic reaction.
• In the oxidative addition direction, we break the A
A−B
B bond and form an M
M−A
A and an M
M−B
B bond.
• The oxidation state (OS), electron count (EC), and coordination number (CN) all increase by two
units during the reaction.
• It is the change in formal oxidation state (OS) that gives rise to the oxidative and reductive part
of the reaction names.
, • Oxidative additions proceed by a great variety of mechanisms,
mechanisms however,
however a vacant 2e
site is always required on the metal.
• We can either start with a 16e complex or a 2e site must be opened up in an 18e
complex by the loss of a ligand producing a 16e intermediate species.
• The change in oxidation state means that the starting metal complex of a given
oxidation state must also have a stable oxidation state two units higher to undergo
oxidative addition (and vice versa for reductive elimination).
• We have seen how neutral ligands such as C2H4 or CO can enter the coordination sphere of a
metal by substitution. We now look at a general method for simultaneously introducing pairs of
anionic ligands, A and B, by the oxidative addition of an A−B molecule such as H2 or CH3‐I.
• The reverse reaction, reductive elimination, leads to the extrusion of A−B from an M(A)(B)
complex and is often the product‐forming step in a catalytic reaction.
• In the oxidative addition direction, we break the A
A−B
B bond and form an M
M−A
A and an M
M−B
B bond.
• The oxidation state (OS), electron count (EC), and coordination number (CN) all increase by two
units during the reaction.
• It is the change in formal oxidation state (OS) that gives rise to the oxidative and reductive part
of the reaction names.
, • Oxidative additions proceed by a great variety of mechanisms,
mechanisms however,
however a vacant 2e
site is always required on the metal.
• We can either start with a 16e complex or a 2e site must be opened up in an 18e
complex by the loss of a ligand producing a 16e intermediate species.
• The change in oxidation state means that the starting metal complex of a given
oxidation state must also have a stable oxidation state two units higher to undergo
oxidative addition (and vice versa for reductive elimination).
