Alternative Catalyst Formats: Catalyst Recovery

Question 1

What is a way to overcome product and catalyst seperation in Homogenous catalysis?

Answer 1

• Using a strategy which combines the best properties of homogenous and heterogenous catalysis - immobilise the ligated transition metal irreversibly on a support
• Allows for efficient catalyst from product mixture seperation
• e.g. immobilisation of a catalyst species via covalent binding of a tethering agent (TA) with a pendant group (PG) of a polymer

Question 2

Polymer supported analogues of catalysts can be attached by a pendant arm to a polymer backbone
What does the position of the attachment strongly affect?

Answer 2

• The position of attachment strongly affects the reactivity and selectivity
• BUT organic polymers have a complex twisted structure that changes (ages) through time
• Therefore can be unsuitable for high temperature and many reagents

Question 3

How does using catalyst immobilisation affect steroisomerism?
Use this as an example

Answer 3

• Large steric barrier from polymer can affect or prevent approach of alkene
• Can change the differentiation between cis and trans alkene
• Can stop catalystic activity completely
• Need optimisation of length, rigidity and physical/chemical nature of tether

Question 4

What are the different attachement of catalyst to the support?

Answer 4

Question 5

This is the catalyst used in metathesis with a support
What does it show

Answer 5

• It take a lot of time and money to architecture a support like that
• Cannot run on a bulk chemical scale

Question 6

How can leaching be an issue with immobilisated catalyst?

Answer 6

• Dissociation of the catalyst and washing away of the catalyst from the support
• The rate of leaching is a very important factor - can lead to loss of high value metal catalyst, health, safety and environmental issues

Question 7

We can modify the ligand to alter intermolecular interactions
For example replace PPh₃ with water soluble phosphines
Why would you do this?

Answer 7

• This ligand makes the catalyst water soluble for easier product separation (like a separating funnel as they are immisible)

Question 8

What is the issue with having an immicible catalyst?
How is this problem partially overcome?

Answer 8

It only reacts at the surface
Can be overcome with stirring however

Question 9

There have also been recent developments in fluorous phase tags
Including: P(CH₂CH₂C₆F₁₃)₃ and CF₃C₆F₁₁
How does it work?

Answer 9

• It is increased in temperature where solvent and organics are all one phase
• The cool down to remove products