Structure-direction of chiral 2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium in the cotemplated synthesis of ferrierite: Fundaments of diastereo-recognition from non-chiral microporous structures

In this work we have explored the structure directing effect of two of the diastereoisomers of the chiral cation 2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (bmpm) in aluminosilicate preparations using tetramethylammonium (TMA) as a co-SDA. The pure SS-bmpm isomer, an equimolar mixture of the RS and SS-bmpm isomers and an enriched mixture in the RS isomer (∼77%) were tested in these preparations and the three succeeded in crystallizing a ferrierite-type material with a larger interlayer distance between the FER sheets than in the fully-condensed FER structure. Molecular mechanics calculations showed that the structure directing ability of the RS isomer to direct the crystallization of the fully-condensed FER structure is lower due to the larger molecular size brougth about by the ‘anti’ configuration of the methyl and the hydroxymethyl substituents, thus suggesting a better structure directing efficiency for the SS isomer. However, the large size of the structure directing agent bmpm forces the FER structure to crystallize with a larger interlayer distance between the FER sheets, canceling the difference in the fitting of the diastereoisomers within the zeolite framework and so preventing the observation of a different structure directing efficiency of the two diastereoisomers in the synthesis of the FER materials.

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► Structure directing effect of two diastereoisomers of a chiral molecule.
► Ferrierite-layered zeolites obtained with different diastereoisomer mixtures.
► Molecular calculations suggest that ferrierite could discriminate between the isomers.
► The size of the chiral structure directing agent leads to a large interlayer space.
► This cancels the differences in the fitting of the two isomers within the structure.