Heterogeneous asymmetric catalysis remains as an exciting research field in chiral catalysis since the heterogeneous catalyst can be separated easily from the reaction mixture compare to conventional homogeneous catalyst. The aim of the research is to develop and investigate a novel heterogeneous asymmetric catalyst using amino acid as chiral promoter. The catalysts were synthesized by attachment of amino acids such as L-glutamic acid, L-leucine and L-phenylalanine onto the hydrophilic part of hydrolyzed octadecyltrichlorosilane (OTS). The short-range order structure of silicon and organic groups in the catalysts has been confirmed by solid-state 29Si and 13C cross-polarization magic-angle-spinning (MAS) NMR spectroscopies, respectively. The solid state MAS NMR results showed that the amino acids interacted with hydrolyzed OTS. This phenomenon was supported by 13C NMR spectra which showed the signals of the peaks of L-glutamic acid, L-leucine and Lphenylalanine were shifted towards a higher magnetic field. It was confirmed by 29Si NMR spectra which showed the peaks of cross-linked –(OH)Si(R)-O-(OH)Si(R)- (R=octadecyl group) whereas those of R–Si≡(OSiR)3 were not present in amino acid-hydrolyzed OTS. This result suggested that the amino acid was attached via cross-linked –(OH)Si(R)-O-(OH)Si(R)- of hydrolyzed OTS. The amino acidhydrolyzed OTS materials were used as catalysts for the asymmetric hydration of epoxycyclohexene to yield two diastereoisomers, namely (1R,2R)-trans-1,2-cyclohexanediol, (1S,2S)-trans-1,2-cyclohexanediol and cis-1,2-cyclohexanediol.
Available at: http://works.bepress.com/hadi_nur/59/