1. Asymmetric Catalysis using Ru- and Fe- based Catalysts
Lecture at Leeds University, 18th October 2018
Prof. Martin Wills, Warwick University. Ru Fe

2. Asymmetric transfer hydrogenation:
A major breakthrough; combination of TsDPEN and a Ru(II) arene:
In contrast:
Mechanism:
or HCO2H
or HCO2Na (aq)
or CO2
a) Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1995, 117, b) Fujii, A.; Hashiguchi, S.; Uematsu, N.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1996, 118,

3. Control of asymmetric reduction is via a cyclic transition state
(the role of the N-H bond is critical for success):
Hydrogen transfer is stepwise but via the substrate orientation illustrated.
Recent work also found a repulsive Arene-SO2 interaction which destabilises the alternative substrate approach.
Dub, P. A.; Gordon, J. C. Dalton Trans. 2016, 45, ) Dub, P. A.; Ikariya, T. J. Am. Chem. Soc. 2013, 135,
Recently applied on 500 kg scale by Pfizer!
OPRD, 2017, 21,

4. Our design: ‘Tethered’ catalysts - to improve versatility:
Could change basis of stereocontrol from electronic to steric:
‘Tether’
h6-aryl cannot rotate; substitutents can be position to control reactions.
Dissociation of ligand should be reduced due to multipoint binding.
Aidan Hayes
Original synthesis by Aidan Hayes; J. Am. Chem. Soc. 2005, 127,

5. Established synthesis of tethered’ diamine catalysts – 3 steps:
(S,S)-enantiomer
Catalyst is air stable – purification commonly achieved using flash chromatography
With Katherine Jolley, Antonio Zanotti-Gerosa et al, Adv. Synth. Catal , 354,

6. Arene-substitution strategy – A new approach to the catalysts:
ESI MS of crude,
DCM, 51h, 90 oC
ligand
Rina Soni, Katherine E Jolley, Guy J. Clarkson and Martin Wills, Org. Lett. 2013, 15, 5110–5113.

7. Arene-substitution strategy – significantly quicker route:
Old route, via a hexadiene: José E. D. Martins, David J. Morris, Bhavana Tripathi and Martin Wills, J. Organomet. Chem., 2008, 693,
New route: synthesis of benzyl-bridged catalysts via an arene-exchange route is much shorter:
Rina Soni, Katherine E. Jolley, Silvia Gosiewska, Guy J. Clarkson, Zhijia Fang, Thomas H. Hall, Ben N. Treloar, Richard C. Knighton, and Martin Wills, Organometallics 2018, 37, 48–64.
Richard C. Knighton, Vijyesh K. Vyas, Luke H. Mailey, Bhalchandra M. Bhanage, Martin Wills, J. Organomet. Chem. 2018, 875, 72-79

8. Tethered catalyst is highly active – 0.01 mol% is effective:
Follow by 1H-NMR:
At 0.01 mol% level,
acetophenone is reduced
in 96% e.e. and 98% yield
after ca. 84 hours!
David Morris

9. Reduction of aryl/heterocyclic ketones.
R,R
J. Org. Chem., 2006, 71, Org. Lett. 2007, 9,

10. Increasing steric hindrance at arene can force steric effects to dominate…but the rate enhancement is valuable:

11. Extension to asymmetric reduction of substituted acetylenic ketones – same directing effect:
Electron-rich
Via:
Electron-poor
Zhijia Fang (Amphi) –
Joined X Zhang group!
Noyori et al., J. Am. Chem. Soc. 1997, 119,
Zhijia Fang and Martin Wills, J. Org. Chem. 2013, 78, 8594–8605.

12. Summary of stereocontrol:

13. Some subtle differences sometimes observed:
Rina Soni, Katherine E Jolley, Guy J. Clarkson and Martin Wills, Org. Lett. 2013, 18, 5110–5113

14. Reduction of electron-rich substrates pose a problem – compare these results in formic acid/triethyamine:
This is the problem:
Conv.
/%:
Electron-poor = fast
Electron-rich = slow
Time/min
Rina Soni, Thomas H Hall, Benjamin P Mitchell, Matthew R Owen, and Martin Wills J. Org. Chem. 2015, 80, 6784−6793.

15. However p-aminoacetophenone can be reduced using the tethered catalysts in water:
Tom
Hall
Rina Soni, Thomas H Hall, Benjamin P Mitchell, Matthew R Owen, and Martin Wills J. Org. Chem. 2015, 80, 6784−6793.

16. N’-alkylated TsDPEN derivatives can also be used:
Catalysts:
Eduardo Martins
S/C=100:1
MeCN added to imine reduction, 28oC, followed by 1H-NMR.
J. E. D. Martins, G. J. Clarkson and M. Wills, Org. Lett. 2009, 11,
T. Koike and T. Ikariya, Adv. Synth. Catal. 2004, 346,

17. Reduction of aryl/alkyne ketones – also challenging;
Which substituent will engage in the CH-p interaction?
Answer – the Aromatic ring, just… with low conversions and low ees!
Low ee because two substrate approaches are competing:

18. Reduction of aryl alkyne ketones – can it be improved?;
Related result – takes advantage of a second directing effect with ortho-phenyl substituted substrates*:
Here the more hindered ring occupies the position from which an in-plane aromatic ring is normally disfavoured due to an unfavourable interaction with the SO2 group (not illustrated). ) Dub, P. A.; Ikariya, T. J. Am. Chem. Soc. 2013, 135,
The same modification works in this situation as well, i.e. introduction of ortho-aryl substituent – now high yield and medium ee!:
* Touge, T.; Nara, H.; Fujiwhara, M.; Kayaki, Y.; Ikariya, T. J. Am. Chem. Soc. 2016, 138,

19. In this case, the alkyne is favoured in the CH-p position:
Vijyesh Vyas, Richard Knighton

20. Same occurs for di-ortho-fluoro substituted substrate:
Vijyesh K. Vyas, Richard C. Knighton, Bhalchandra M. Bhanage, and Martin Wills, Org. Lett. 2018, 20, 975–978

21. Selectivity is even higher when alkyne is made more electron-rich – now get very high ees:
Vijyesh K. Vyas, Richard C. Knighton, Bhalchandra M. Bhanage, and Martin Wills, Org. Lett. 2018, 20, 975–978

22. Application to a synthetic target:
Summary of selectivity (R,R catalyst):
* Leblanc, M.; Fagnou, K. Org. Lett. 2005, 7,

23. VERY challenging ketone substrates – 1,3 dialkoxy propanones – can we get a high ee?:
Sam Forshaw

24. Sam Forshaw, Alexander J. Matthews, Thomas J. Brown, Louis J
Sam Forshaw, Alexander J. Matthews, Thomas J. Brown, Louis J. Diorazio, Luke Williams and Martin Wills, Org. Lett, 2017, 17,

25. Dynamic Kinetic Resolution of ferrocenyl ketones, with Prof Weiping Chen (Xi’an):
Ruixia Liu, Gang Zhou, Thomas H. Hall, Guy J Clarkson, Martin Wills, and Weiping Chen, Adv. Synth. Catal. 2015, 357,

26. Reductions of challenging ketones – remote N vs OR group:
Renta Jonathan Chew and Martin Wills J. Catal. 2018, 361,
Reduction of iminium salts:
Renta Jonathan Chew and Martin Wills J. Org. Chem. 2018, 83, 2980–2985.

27. Iron-based catalysts for hydrogen transfer reactions.
Future Challenges:
Iron-based catalysts for hydrogen transfer reactions. 7 Mn Tc Re 8 Fe Ru Os 9 Co Rh Ir
Fe-H: Knölker, H.-J.; Baum, E.; Goesmann, H.; Klauss, R. Angew. Chem. Int. Edn. 1999, 38,
Used in pressure and transfer hydrogenation: Casey, C. P.; Guan, H. J. Am. Chem. Soc. 2009, 131,
Asymmetric catalysis using iron complexes – ‘Ruthenium Lite’? M. Darwish and M. Wills, Catal. Sci. Technol. 2011, 2,

28. Mechanism of Fe-catalysed hydrogen transfer:
a) Hydride formation:
b) Hydrogen transfer:
Our application in a ketone oxidation:
Tarn C. Johnson, Guy J. Clarkson and Martin Wills, Organometallics,
2011, 30,

29. Iron complexes for hydrogen borrowing… A good result!
Mechanism:
Overall reaction:
Products formed:
Andrew Rawlings:
Andrew J. Rawlings, Louis J. Diorazio, and Martin Wills, Org.Lett. 2015, 17, (51 citations to date).

30. Iron complexes for hydrogen borrowing- update on unsaturated substrates:
Catalyst used:
Thomas Brown:
Thomas J. Brown, Madeleine Cumbes, Louis J. Diorazio, Guy J. Clarkson and Martin Wills, J.Org. Chem. 2017, 82, 10489–10503.

31. Asymmetric Fe-Shvo catalysts - design:
R1=Me, R2=TBDMS
Best result so far:
Jonathan P. Hopewell, José E. D. Martins, Tarn C. Johnson, Jamie Godfrey and Martin Wills, Org. Biomol. Chem. 2012, 10,

32. How can this be improved?
Asymmetric Fe-Shvo catalysts; speculated reduction stereochemical control.
How can this be improved?
Jonathan Hopewell
Tarn Johnson
Jonathan P. Hopewell, José E. D. Martins, Tarn C. Johnson, Jamie Godfrey and Martin Wills, Org. Biomol. Chem. 2012, 10,

33. Chiral Tricarbonyl(cyclopentadienone)iron Complexes:
Up to 32% ee in the asymmetric hydrogenation of acetophenone
Berkessel, A. et al.
Berkessel, A. et al. Organometallics 2011, 30, 3880.
Berkessel, A. et al. ChemCatChem, 2011, 3, 861.
Up to 50% ee in the asymmetric hydrogenation of acetophenone
Gennari, C. et al.
Gennari, C. et al. Eur. J. Org. Chem. 2015, 1887.
Our idea:
(Starting from diols made using the tethered catalyst)
Roy C. Hodgkinson, Alessandro Del Grosso, Guy J. Clarkson and Martin Wills, Dalton Trans., 2016, 45, 3992 – 4005.

34. Reduction of Acetophenone – effective, but still low ee:
Catalyst
Temp oC
Time h
Activator
Conv % ee % 80 18
11.5
----
K2CO3 (5%)
99.7
TMAO (1%)
99.8
5.6 (S)
18.9
9.0 (S)
100 24
7.0
3.0 (S)
8.2 (S)
54.6
7.0 (S)
93.4
18.0
6.0 (S)
99.6
6.6 (S)
42.0
13.8 (R)
59.4
14.8 (R)
9.0
13.0 (R)
12.5 (R)
31.1
20 (R)
33.5
17.6 (R)
12.0
6.0 (R)
71.9
The O-silylate complex gave opposite enantiomer to the diol and O-benzylate complex.
Higer conversion is achieved lowering the temperature.
The use of TMAO as activator resulted in almost full conversion.
The iron tricarbonyl catalysed the reaction also in absence of activator.
Roy C. Hodgkinson, Alessandro Del Grosso, Guy J. Clarkson and Martin Wills, Dalton Trans., 2016, 45, 3992 – 4005.

35. Other iron complexes prepared in attempt to increase ee:
OR = OBn
Up to 21% ee in
acetophenone
hydrogenation
OR = OH
Up to ca. 10% ee in acetophenone hydrogenation.
Reaction
Catalyst (%) Obn series…
Activator (%)
Solvent
Conv Ee
ADG364
ADG358 (1%) OBn4
IPA/H2O
4.8
25.2 (R)
ADG363
K2CO3 (5%)
>99
23.2 (R)
ADG362
TMAO (1%)
23 (R)
ADG379
ADG372 (1%) OBn2
3.4 (R)
ADG380 12
5.2 (R)
ADG381
3.2 (R)
ADG421
ADG414 (1%) OBn OTBS
TMAO 1%
85.2%
12% (R)
Alessandro Del Grosso, Alexander E. Chamberlain, Guy J. Clarkson and Martin Wills*, Dalton Trans. 2018, 47,

36. Table 6; Asymmetric transfer hydrogenation of acetophenone using complexes XX and XX.
Reaction
Catalyst (%)
Activator (%)
Conv
Formate (ee)
Alcohol (ee)
ADG368
ADG358 (10%) OBn4
TMAO (10%)
55.7
7.8 (35.8 R)
47.9 (35.6 R)
ADG378
ADG372 (10%) OBn2
96.2
7.9 (26.4 R)
88.3 (25.8 R)
Alessandro Del Grosso, Alexander E. Chamberlain, Guy J. Clarkson and Martin Wills*, Dalton Trans. 2018, 47,

37. Technology Strategy Board.
Acknowledgements
Research Group Contributors
(also listed in talk)
Former group members:
Dr Eduardo Martins (Postdoc)
Dr Rina Soni (PhD 2011, and postdoc)
Katherine Jolley (PhD student)
Zhijia Fang (PhD 2013)
Alessandro Del Grosso (PDRA)
Richard Knighton (PDRA)
Vijyesh Vyas (Newton-Bhabha visitor)
Jonathan Renta Chew (A*STAR fellow)
Current group members
Tom Hall (PhD)
Jonathan Chew (PDRA)
Thomas Brown (PhD)
Sam Forshaw (PhD)
Collaborators and technical staff
Guy Clarkson (X-rays)
David Fox (Kinetics), Adam Clark, Ivan Prokes (NMR), Lijang Song (MS).
Sponsors and Industrial Collaborators
Engineering and Physical Sciences Research Council (EPSRC).
Leverhulme Trust.
Astrazeneca – Mark Graham, Louis Diorazio.
Warwick University WPRF/CIS PG Scheme.
Arran Chemicals – Peter Cairns.
Johnson Matthey – Fred Hancock, Antonio Zanotti-Gerosa, Hans Nedden.
Technology Strategy Board.

38. Technology Strategy Board.
Acknowledgements
Research Group Contributors
(also listed in talk)
Dr Aidan Hayes (PhD 2005)
Dr David Morris (PhD 2000, PDRA)
Dr Tarn Johnson (PhD 2012)
Dr Jon Hopewell (Postdoc)
Dr Eduardo Martins (Postdoc)
Dr Rina Soni (PhD 2011)
Katherine Jolley (Final year PhD student)
Zhijia Fang (PhD 2013)
Andrew Rawlings (MSc)
Tom Hall (PhD)
Roy Hodgkinson (PDRA)
Alessandro Del Grosso (PDRA)
Thomas Brown (PhD)
Lavrentis Galanopoulos (MSc student)
Collaborators and technical staff
Guy Clarkson (X-rays)
David Fox (Kinetics), Adam Clark, Ivan Prokes (NMR), Lijang Song (MS).
Prof Peter O’Connor (MS)
Cookson Chiu (MS)
Sponsors and Industrial Collaborators
Engineering and Physical Sciences Research Council (EPSRC).
Leverhulme Trust.
Astrazeneca – Mark Graham, Louis Diorazio
Warwick University WPRF PG Scheme.
Arran Chemicals – Peter Cairns.
Johnson Matthey – Fred Hancock, Antonio Zanotti-Gerosa.
Technology Strategy Board.

39. Any questions? Alessandro del Grosso.
Vijyesh Vyas, Richard Knighton, Martin Wills,
Ren Ta Jonathan Chew, Anish Mistry. 39

40. Any questions? 40