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

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

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 2632013, 1953

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 3715334, 1973

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

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

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

Alkynes Hydrosilylation 1 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

Alkynes Hydrosilylation Mechanism 1 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

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

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

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

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

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

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 2012. b) Berthon- Gelloz, G.; Markó, I. E. In N-Heterocyclic Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley, 2006 14

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 !