Transition Metal Frustrated Lewis Pairs for Small Molecule Activation

Key words:Lewis acid, Lewis base, adduct, catalysis, lone pairs

Small molecules, such as carbon dioxide (CO2), hydrogen (H2)and ethene (C2H4), have the potential to become sustainable building blocks for industrial processes as they can be derived from bio-mass sources. Carbon dioxide and ethene are also greenhouse gases if released from industrial processes rather than being recycled. It is important to find useful synthetic methods which incorporate these potentially carbon neutral small molecules as current feedstocks deplete. The catalytic transformation of most of these small molecules can be quite challenging with the initial activation being the major obstacle.

Lewis bases (LB) donate a lone pair of electrons into a vacant orbital of a Lewis acid (LA) to form a classical Lewis adduct. However, if surrounding groups are very sterically hindering (bulky) then the Lewis base and Lewis acid will be too far away from each other to form a bond and form a frustrated Lewis pair (FLP). The unquenched reactivity of the Lewis base and Lewis acid leads to a very high energy molecule which can activate small molecules in various ways. Initially Group 15 elements were used as Lewis bases and Group 13 elements were used as the Lewis acids.

More recently our research groups we have been using transition metals as either the Lewis acid or the Lewis base of the FLP combined with a main group compound. Early transition metals in high oxidation state are good for use as a Lewis acid due to being very electron poor. In our research, we have used a zirconium(IV) complex with a phosphine (PH3) for small molecule activation. We have also shown the use of late transition metals in high oxidation states, as they are very electron rich, as Lewis bases in combination with a borane. The example shows how we have used a platinum(0) complex with tris(pentafluorophenyl)borane (BCF) to activate small molecules such as H2, CO2 and C2H4 (figure 1),

What is actually being produced by these small molecules? Have these got any use? Can you put the simple formulae of the producs/reactant is thereaction scheme?

There needs to be a conclusion paragraph.


Krishna Mistry is a postgraduate researcher assistant at the School of Chemistry, University of Bristol. During her PhD,she is focused upon

She is currently investigating the. COMPLETE, ADD SOMETHING ABOUT CDT, Change photo

Transition Metal Frustrated Lewis Pairs for Small Molecule Activation

Questions

  1. Name an element in Group 13. [1 mark]
  2. Daw a dot and cross diagram of a boron trifluoride (BF3). [1 mark]
  3. Is BF3 a Lewis acid or Lewis base? [1 mark]
  4. Is phosphine a Lewi acid or Lewis base? [1 mark]
  5. Draw a Lewis Adduct formed fromBF3and phosphine[2 marks]
  6. What does the Roman numeral after the elements in the text signify e.g. in ‘zirconium(IV)’? [1 mark]
  7. What is the molar mass of tris(pentafluorophenyl)borane? [1 mark]
  8. The reaction of ethene with the Lewis adduct has a yield of @@@@ %. What mass of product can be isolated from 50 g of ethene? [2 marks]

Extension Question

Explain why the use of catalysts generally can be considered an aspect of ‘green chemistry’. [3 marks]

Transition Metal Frustrated Lewis Pairs for Small Molecule Activation

Questions

  1. Name an element in Group 13. [1 mark]
  1. Daw a dot and cross diagram of a boron trifluoride (BF3). [1 mark]
  1. Is BF3 a Lewis acid or Lewis base? [1 mark]
  1. Is phosphine a Lewi acid or Lewis base? [1 mark]
  1. Draw a Lewis Adduct formed from BF3and phosphine [2 marks]
  1. What does the Roman numeral after the elements in the text signify e.g. in ‘zirconium(IV)’? [1 mark]
  1. What is the molar mass of tris(pentafluorophenyl)borane? [1 mark]
  1. The reaction of ethene with the Lewis adduct has a yield of @@@@ %. What mass of product can be isolated from 50 g of ethene? [2 marks]

Extension Question

Explain why the use of catalysts generally can be considered an aspect of ‘green chemistry’. [3 marks]

Transition Metal Frustrated Lewis Pairs for Small Molecule Activation

Answers

{To be written later}