1. The Ph.D. Students’ Day Steve Dierick István E. Markó
Hydrosilylation of Alkenes and Alkynes Catalyzed by NHC Platinum(0) Complexes
The Ph.D. Students’ Day
Steve Dierick
István E. Markó
June 1, 2012
Louvain-la-Neuve

2. Outline 1. What is the hydrosilylation reaction?
2. Hydrosilylation of C−C multiple bonds with Platinum(0) carbene complexes
a) 1st generation catalyst in alkenes hydrosilylation
The breakthrough
b) 1st and 2nd generation catalysts in alkynes hydrosilylation
More challenging substrates
c) 3rd generation catalyst in alkenes and alkynes hydrosilylation
How serendipity, intuitions and detailed mechanistic studies lead to discovery
3. Conclusions and Perspectives

3. Hydrosilylation Addition of a Si−H unit across multiple bonds1
Straightforward and atom-economical formation of Si−C bonds2
→ second most important reaction in the silicone industry
→ used for the production of silicone-based polymers, fluids, surfactants,
adhesives etc…
Since 1953, transition metals, particularly platinum, are used extensively as catalysts for this transformation3
1. Marciniec, B.; Maciejewski, H.; Pietraszuk, C.; Pawluć, P. In Hydrosilylation: A Comprehensive Review on Recent Advances; Marciniec, B., Ed.; Springer: New York, 2009
2. Troegel, D.; Stohrer, J. Coord. Chem. Rev. 2011, 255, 1440
3. Wagner, G. H. (Union Carbide) U.S. Patent , 1953

4. Birth of the Research Project
Since 1973, the Karstedt catalyst1 is widely used in industry
despite its limitations:
Industrial waste!
Product coloration!
Platinum colloids are formed through ligands dissociations
Alkanes are produced by hydrogenation on platinum colloids
Isomerized olefins originate from unselective catalysis
1. Karstedt, B. D. (General Electric) U.S. Patent , 1973

5. Birth of the Research Project
How could all these shortcomings be tackled?
Through stabilization of the platinum species involved
→ avoid platinum colloids and thus hydrogenation
Via the fine tuning of the catalyst properties
→ control the catalyst reactivity and selectivity
Both objectives might be addressed by introducing
a strongly binding ancillary ligand on platinum! 4

6. A Novel Family of Pt(0) Catalysts
Readily available
Stable towards air and moisture
Non-hygroscopic
Indefinitely storable
Easy to handle
Dierick, S.; Bastug, G.; Markó, I. E. Org. Synth. 2012, accepted
Berthon-Gelloz, G.; Schumers, J.-M.; Lucaccioni, F.; Tinant, B.; Wouters, J.; Markó, I. E. Organometallics 2007, 26, 5731 5

7. Alkenes Hydrosilylation
No colloids
Markó, I. E.; Stérin, S.; Buisine, O.; Mignani, G.; Branlard, P.; Tinant, P.; Declercq, J.-P.
Science 2002, 298, 204
Markó, I. E.; Stérin, S.; Buisine, O.; Berthon, G.; Michaud, G.; Tinant, B.; Declercq, J.-P.
Adv. Synth. Catal. 2004, 346, 1429 6

8. Alkynes Hydrosilylation1 2
More labile dienes increase the selectivity and the reaction rate but the complexes are less stable
Increased steric hindrance on the NHC enhance the selectivity and the reaction rate
De Bo, G.; Berthon-Gelloz, G.; Tinant, B.; Markó, I. E. Organometallics 2006, 25, 1881
Berthon-Gelloz, G.; Schumers, J.-M.; De Bo, G.; Markó, I. E. J. Org. Chem. 2008, 73, 4190 7

9. Alkynes Hydrosilylation Mechanism1 2
Increased steric
hindrance 1 1 2
More labile diene
De Bo, G.; Berthon-Gelloz, G.; Tinant, B.; Markó, I. E. Organometallics 2006, 25, 1881
Berthon-Gelloz, G.; Schumers, J.-M.; De Bo, G.; Markó, I. E. J. Org. Chem. 2008, 73, 4190 8

10. Alkynes Hydrosilylation
Advanced Intermediate in the total synthesis of Lactimidomycin
Gallenkamp, D.; Fürstner, A. J. Am. Chem. Soc. 2011, 133, 9232
Berthon-Gelloz, G.; Schumers, J.-M.; De Bo, G.; Markó, I. E. J. Org. Chem. 2008, 73, 4190 9

11. Silylated Alkynes Hydrosilylation
[Pt0]
mol%
Activation (h)
Time (h)
Ratio β : α
GC Purity (%)
Yield (%)
(IPr)Pt(AE)
0.1 - 36
7.8 : 1
n.d.
(100) 2 18
9.4 : 1 91 87 1 3
13 : 1 95 84
(IPr)Pt(dvtms) 94 88
The reaction is sluggish and affords low selectivities:
→ silylated alkynes promote the deactivation pathways!
Serendipity
Optimisation of the reaction conditions: catalyst loading, temperature, silane, dilution, slow addition, addition order, reagents purity, inert atmosphere…
→ 1st and 2nd generation catalysts give the same results?!
There must be a common intermediate !
Intuition
Dierick, S.; Markó, I. E. Unpublished results 10

12. Alkynes Hydrosilylation Mechanism Detailed mechanistic studies
Strongly bound silylated alkynes trigger NHC elimination!
Intuition
Common intermediate to 1st and 2nd generation catalysts
Detailed mechanistic studies
Dierick, S.; Vercruysse, E.; Markó, I. E. Manuscript in preparation
De Bo, G.; Berthon-Gelloz, G.; Tinant, B.; Markó, I. E. Organometallics 2006, 25, 1881
Berthon-Gelloz, G.; Schumers, J.-M.; De Bo, G.; Markó, I. E. J. Org. Chem. 2008, 73, 4190 11

13. 3rd Generation Hydrosilylation Catalyst
[Pt0]
Time (min)
Ratio β : α
Yield (%)
(IPr)Pt(dvtms)
420
12 : 1 95
(IPr)Pt(AE)
240
16 : 1
(IPr)Pt(SiMe2Ph)2
< 15
23 : 1 96
→ best catalyst developed to date!
Berthon-Gelloz, G.; de Bruin, B.; Tinant, B.; Markó, I. E. Angew. Chem., Int. Ed. 2009, 48, 3161
Dierick, S.; Vercruysse, E.; Markó, I. E. Manuscript in preparation 12

14. 3rd Generation Hydrosilylation Catalyst
Dierick, S.; Bastug, G.; Markó, I. E. Org. Synth. 2012, accepted
Dierick, S.; Vercruysse, E.; Markó, I. E. Manuscript in preparation 13

15. Conclusions & Perspectives
NHC Platinum(0) complexes are the ideal user-friendly reagents for the hydrosilylation of alkenes and alkynes:
Exploration of the selectivity between C−C multiple bonds
Hydrosilylation of challenging allyl substrates
Asymmetric version of the process
High activity
Readily available
High selectivity
Indefinitely storable
Low catalyst loading
Easy to handle
Catalysts samples are available on request!
We are always open to new collaborations!
For reviews on NHC Pt(0) complexes, see: a) Dierick, S.; Markó, I. E. “(IPr)Pt(dvtms)” In Encyclopedia of reagents for Organic Synthesis (e-EROS); Wiley, ASAP b) Berthon- Gelloz, G.; Markó, I. E. In N-Heterocyclic Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley, 2006 14

16. Acknowledgment Hydrosilylation family: Dr. Buisine, O. Dr. Stérin, S.
Dr. Michaud, G.
Dr. Berthon, G.
Dr. De Bo, G.
Dr. Schumers, J.-M.
Flamant, M.
Vercruysse E.
Prof. Markó group:
Himself
Lucaccioni, F.
All my colleagues !
Financial support:
UCL, FRIA, FNRS, ARC
Rhodia Silicones, Umicore
The organising committee and YOU !