1042011-40-4Relevant academic research and scientific papers
Catalytic Olefin Hydrosilations Mediated by Ruthenium η3-H2Si σ Complexes of Primary and Secondary Silanes
Lipke, Mark C.,Poradowski, Marie-Noelle,Raynaud, Christophe,Eisenstein, Odile,Tilley, T. Don
, p. 11513 - 11523 (2018)
Unambiguous examples of η3-H2SiH(R) complexes featuring a terminal Si-H bond have been prepared and examined as possible intermediates in olefin hydrosilation. These species were generated by displacement of the secondary silane ligands in [PhBPPh3]RuH[η3-H2SiMePh] (1b) (PhBPPh3 = PhB(CH2PPh2)3- by primary silanes RSiH3 to generate [PhBPPh3]RuH[η3-H2SiH(R)] (R = Cy (1d), CH2CH2Ph (1e), Trip = 2,4,6-iPr3C6H2 (1f)). Complexes 1d and 1e were characterized in solution, whereas 1f was isolated and studied in detail. Complex 1b is not a competent precatalyst for the hydrosilation of 1-hexene with CySiH3, whereas comparable conditions gave reasonable yields for the selective anti-Markovnikov hydrosilations of Cl3SiCH2CH=CH2 (89%), p-chlorostyrene (73%), and allyl chloride (70%). The 1H NMR spectrum of 1f collected at -30 °C displays a downfield signal (δ = 8.26 ppm) for the terminal Si-H bond that suggests electronic similarities between 1f and cationic silylene dihydrides [Cp?(iPr3P)Ru(H)2=SiH(R)]+ that mediate olefin hydrosilations via the direct insertion of the C=C bond into the terminal Si-H bond. However, further mechanistic considerations, including results on the hydrosilation of p-chlorostyrene with the secondary silane Et2SiH2 and [PhBPPh3]RuH[η3-H2SiEt2] (1a) as the catalyst, indicate that an insertion mechanism involving a Ru-H (rather than a Si-H) group is possible. DFT investigations of the hydrosilation of several olefins with CySiH3 using 1d as the catalyst reveal a preferred pathway involving olefin insertion into a Ru-H bond followed by migration of the resulting alkyl group to the silicon atom of an η3-H2SiH(Cy) ligand. The latter process occurs via an unusual transition state in which a Ru-H-Si linkage acts as a pivot point to facilitate a Si-H bond cleavage/Si-C bond formation step that is otherwise similar to those involving the kite-shaped four-center transition states of σ-bond metathesis. Direct insertion into the Si-H bond is the next lowest accessible pathway.
Alkene hydrosilation by a cationic hydrogen-substituted iridium silylene complex
Calimano, Elisa,Tilley, T. Don
supporting information; body text, p. 9226 - 9227 (2009/02/02)
A cationic hydrogen-substituted iridium silylene complex [(PNP)(H)Ir=Si(Mes)H][B(C6F5)4] (2) was synthesized via hydride abstraction from the corresponding neutral iridium silyl hydride complex. DFT calculations for 2 indicate that the cationic charge is localized at the silicon center and depict a LUMO with predominant silicon p-orbital character. Notably, complex 2 reacts rapidly with unhindered alkenes at ambient temperatures to afford disubstituted silylene complexes via Si-C bond formation. Complex 2 is also the catalyst for alkene hydrosilation of primary silanes with a high degree of anti-Markovnikov selectivity. Copyright
