Hydrosilylation of carbonyl-containing substrates catalyzed by an electrophilic η1-silane iridium(III) complex

Sehoon Park, Maurice Brookhart*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

111 Scopus citations

Abstract

Hydrosilylation of a variety of ketones and aldehydes using the cationic iridium catalyst (POCOP)Ir(H)(acetone)+, 1 (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl), is reported. With triethyl silane, all but exceptionally bulky ketones undergo quantitative reactions employing 0.5 mol % catalyst in 20-30 min at 25 °C. Hydrosilylation of esters and amides results in over-reduction and cleavage of C-O and C-N bonds, respectively. The diastereoselectivity of hydrosilylation of 4-tert-butyl cyclohexanone has been examined using numerous silanes and is highly temperature dependent. Using EtMe2SiH, analysis of the ratio of cis:trans hydrosilylation products as a function of temperature yields values for ΔΔH (ΔH(trans) - ΔH (cis)) and ΔΔS (ΔS (trans) - ΔS(cis)) of -2.5 kcal/mol and -6.9 eu, respectively. Mechanistic studies show that the ketone complex (POCOP)Ir(H)(ketone)+ is the catalyst resting state and is in equilibrium with low concentration of the silane complex (POCOP)Ir(H)(HSiR 3)+. The silane complex transfers R3Si + to ketone, forming the oxocarbenium ion R3SiOCR' 2+, which is reduced by the resulting neutral dihydride 3, (POCOP)Ir(H)2, to yield product R3SiOCHR'2 and (POCOP)IrH+, which closes the catalytic cycle.

Original languageEnglish
Pages (from-to)6057-6064
Number of pages8
JournalOrganometallics
Volume29
Issue number22
DOIs
StatePublished - 22 Nov 2010

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