The enantioselective cyanosilylation of aldehydes on a chiral VO(Salen) complex encapsulated in SBA-16

A solid catalyst for enantioselective cyanosilylation of aldehydes was prepared by encapsulating a chiral vanadyl Salen complex [VO(Salen)] in the nanocage of SBA-16. After encapsulation, the pore entrance size of SBA-16 was finely tuned through a silylation method to confine the metal complex in the nanocage and allow the free diffusion of the reactants and products during the catalytic process. For the enantioselective cyanosilylation of benzyldehyde, the enantioselectivity of the solid catalyst can achieve as high as 90%. When alkanes such as pentane, hexane and heptane were used as solvents, VO(Salen) confined in the nanocage of SBA-16 exhibits higher enantioselectivity than its homogeneous counterpart. In halogenated alkanes, the enantioselectivity of VO(Salen) confined in the nanocage of SBA-16 is lower than that of the homogeneous catalyst. The different solvent effect for the solid catalyst from the homogeneous counterpart is probably due to the altered microenvironment of VO(Salen) encapsulated in the nanocage.