Development and mechanistic investigation of a highly efficient iridium(V) silyl complex for the reduction of tertiary amides to amines

TY - JOUR

T1 - Development and mechanistic investigation of a highly efficient iridium(V) silyl complex for the reduction of tertiary amides to amines

AU - Park, Sehoon

AU - Brookhart, Maurice

PY - 2012/1/11

Y1 - 2012/1/11

N2 - The cationic Ir(III) acetone complex (POCOP)Ir(H) 2(acetone) + (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) was shown to catalyze the reduction of a variety of tertiary amides to amines using diethylsilane as reductant. Mechanistic studies established that a minor species generated in the reaction, the neutral silyl trihydride Ir(V) complex (POCOP)IrH 3(SiEt 2H), was the catalytically active species. High concentrations of this species could be conveniently generated by treatment of readily available (POCOP)IrHCl with tert-butoxide in the presence of Et 2SiH 2 under H 2. Thus, using this mixture in the presence of a trialkylammonium salt, a wide array of tertiary amides, including extremely bulky substrates, are rapidly and quantitatively reduced to tertiary amines under mild conditions with low catalyst loading. A detailed mechanistic study has been carried out and intermediates identified. In brief, (POCOP)IrH 3(SiEt 2H) reduces the amide to the hemiaminal silyl ether that, in the presence of a trialkylammonium salt, is ionized to the iminium ion, which is then reduced to the tertiary amine by Et 2SiH 2. Good functional group compatibility is demonstrated, and a high catalyst stability has provided turnover numbers as high as 10 000.

AB - The cationic Ir(III) acetone complex (POCOP)Ir(H) 2(acetone) + (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) was shown to catalyze the reduction of a variety of tertiary amides to amines using diethylsilane as reductant. Mechanistic studies established that a minor species generated in the reaction, the neutral silyl trihydride Ir(V) complex (POCOP)IrH 3(SiEt 2H), was the catalytically active species. High concentrations of this species could be conveniently generated by treatment of readily available (POCOP)IrHCl with tert-butoxide in the presence of Et 2SiH 2 under H 2. Thus, using this mixture in the presence of a trialkylammonium salt, a wide array of tertiary amides, including extremely bulky substrates, are rapidly and quantitatively reduced to tertiary amines under mild conditions with low catalyst loading. A detailed mechanistic study has been carried out and intermediates identified. In brief, (POCOP)IrH 3(SiEt 2H) reduces the amide to the hemiaminal silyl ether that, in the presence of a trialkylammonium salt, is ionized to the iminium ion, which is then reduced to the tertiary amine by Et 2SiH 2. Good functional group compatibility is demonstrated, and a high catalyst stability has provided turnover numbers as high as 10 000.

UR - http://www.scopus.com/inward/record.url?scp=84862908135&partnerID=8YFLogxK

U2 - 10.1021/ja209567m

DO - 10.1021/ja209567m

M3 - 文章

C2 - 22091749

AN - SCOPUS:84862908135

SN - 0002-7863

VL - 134

SP - 640

EP - 653

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 1

ER -