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

TY - JOUR

T1 - Hydrosilylation of carbonyl-containing substrates catalyzed by an electrophilic η1-silane iridium(III) complex

AU - Park, Sehoon

AU - Brookhart, Maurice

PY - 2010/11/22

Y1 - 2010/11/22

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=78649232308&partnerID=8YFLogxK

U2 - 10.1021/om100818y

DO - 10.1021/om100818y

M3 - 文章

AN - SCOPUS:78649232308

SN - 0276-7333

VL - 29

SP - 6057

EP - 6064

JO - Organometallics

JF - Organometallics

IS - 22

ER -