Download Activity 5 – Catalytic Cycles

Activity 5 – Catalytic Cycles
We will look at a number of catalytic cycles below, but first it is useful to think about the key
steps which make up all the catalytic cycles.
1) Oxidative Addition (Figure 7). In this step the metal in the centre loses electrons
to the ligands as the ligand are added to the metal centre, hence the name –
oxidative due to oxidation of the metal centre and addition – as the ligand is
added to the complex.
Figure 71. Mechanism of oxidative addition
2) Reductive Elimination (Figure 8). In this step the ligands are lost from the
complex (elimination) whilst the metal centre gains electrons (reductive).
Figure 2. Mechanism of reductive elimination
3) Β-hydride Shift/Alkene Insertion (Figure 9). Here a hydrogen from the second
carbon away from the carbon which joins to the metal centre moves to join the
metal centre whilst the metal bonded alkane is transformed into an alkene.
Alkene insertion is the reverse of this reaction.
Figure 3. Mechanism of β-hydride shift
4) Alkyl Migration (Figure 10). An alkyl group which starts off attached to the metal
centre moves to become part of one of the other ligands.
Figure 4. Mechanism of alkly migration
5) Addition/Subtration of a Ligand (Figure 11). This is the most straightforward step.
A ligand simply attaches to or detaches from the central metal ion.
Figure 5. Mechanism of ligand addition
Using these steps we can understand what is going on in complex catalytic cycles.
Hydrogenation
Figure 6. Catalytic cycle for the hydrogenation of a generic alkene with mechanism
steps labelled.
Hydroformylation
Figure 7. Catalytic cycle for the hydroformylation of a generic alkene with mechanism
steps labelled.
Question: Can you find any other catalytic cycles? See if you can identify the steps using
the breakdown above.