The hydrosilylation of alkenes and alkynes catalyzed by N-heterocyclic carbene platinum(0) complexes
(2007)
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- Authors
- Supervisors
- Marko, Istvan
- Abstract
- (en) This PhD deals with the fundamental understanding of the hydrosilylation of alkene and alkynes catalyzed by N-heterocyclic carbene platinum(0) complexes ((NHC)Pt(dvtms)). These catalysts have been found to be uniquely selective for the hydrosilylation of alkenes and yield low amounts of isomerized alkene byproducts (< 3%). The detailed mechanistic study of the mode of action of (NHC)Pt(dvtms) complexes has revealed that the high selectivity observed is due to their capability to act as stable reservoirs of catalytically active species, which are very slowly liberated during the course of the hydrosilylation. The slow-release of the active catalyst is the key factor in minimizing the amount of isomerized alkenes formed throughout the reaction. Moreover, the mechanistic study pointed towards the possibility of a unique hydrosilylation mechanism, whereby the oxidative addition of the silane step and the migratory insertion of the alkene would be combined in one concerted operation. Alkynes have been found to undergo a highly regioselective hydrosilylation, in favor of the â-(E)-regioisomer, with the (IPr)Pt(AE) complex. This complex was designed through the understanding of the catalyst activation and the steric factors governing the regioselectivity of the silane addition. The (IPr)Pt(AE) complex represents the state-of-the-art for the generation of beta-(E)-vinylsilanes through the hydrosilylation of alkynes. Insights into the mode of action of (IPr)Pt(AE) has enabled us to isolate the unprecedented (IPr)Pt(SiMe2Ph)2 complex which is a very potent and regioselective hydrosilylation catalyst. Interestingly, the X-ray structure, 195Pt NMR, and reactivity of the (IPr)Pt(SiMe2Ph)2 complex all indicate that this complex represents a snapshot of the oxidative addition process of a disilane onto a Pt(0) center. Hypotheses made on the steric bulk of NHC ligands prompted us to design a novel class of sterically hindered NHCs.
- Affiliations
Citations
Berthon-Gelloz, G. (2007). The hydrosilylation of alkenes and alkynes catalyzed by N-heterocyclic carbene platinum(0) complexes. https://hdl.handle.net/2078.5/65176