(R)-(+)-Binol-functionalized mesoporous organosilica as a highly efficient pre-chiral catalyst for asymmetric catalysis.
(R)-(+)-Binol-functionalized chiral periodic mesoporous organosilicas (PMOs) with different framework compositions were successfully synthesized by cocondensation of (R)-2,2'-di(methoxymethyl)oxy-6,6'-di(1-propyltrimethoxysilyl)-1,1'-binaphthyl (BSBinol) with 1,2-bis(trimethoxysilyl)ethane (BTME) and tetramethoxysilane (TMOS) using triblock copolymer P123 as a template in acidic solution. The mixture of BTME and BSBinol can result in a highly ordered mesostructure in an acidic medium but the mesoporous materials synthesized using a mixture of TMOS and BSBinol can only be obtained in a weak acidic buffer solution. All the materials are efficient catalysts (coordinated with Ti) for asymmetric addition of diethylzinc to aldehydes. The chiral PMO with ethane and (R)-(+)-Binol in the framework exhibits an enantioselectivity as high as 90% with a turnover frequency (TOF) of 104 h(-1), which is even higher than the homogeneous (R)-(+)-Binol catalyst (83% ee with TOF of 96 h(-1)) using toluene as solvent under similar conditions. This work demonstrates the positive effect of the rigid pore wall in increasing the enantioselectivity of the chiral PMOs.
Liu
Xiao
X
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences Institution, 457 Zhongshan Road, Dalian 116023, China.
Wang
Peiyuan
P
Yang
Yan
Y
Wang
Peng
P
Yang
Qihua
Q
D000447:Aldehydes / Q000737:chemistry; D002384:Catalysis; D004980:Ethane / Q000031:analogs & derivatives / Q000737:chemistry; D009281:Naphthalenes / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry; D016062:Porosity; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism; D014297:Trimethylsilyl Compounds / Q000737:chemistry
D000447:Aldehydes; D009281:Naphthalenes; D009942:Organometallic Compounds; C475744:S(-)2,2'-dihydroxy-1,1'-binaphthyl; D012821:Silanes; D012997:Solvents; D014297:Trimethylsilyl Compounds; C517344:bis(trimethoxysilyl)ethane; C061205:tetramethoxysilane; D012822:Silicon Dioxide; D004980:Ethane; C454811:diethylzinc