Diastereomer Resolution of M₄L₆ Coordination Cages by Ultra‐High‐Resolution Ion‐Mobility Mass Spectrometry

Abstract

Coordination cages can be used for enantioand regioselective catalysis and for the selective sensing and separation of isomeric guest molecules. Here, stereoisomers of a family of coordination cages are resolved using ultra-high-resolution cyclic ion-mobility mass spectrometry (cIM-MS). The observed ratio of diastereomers is dependent on both the metal ion and counter ion. Moreover, the point groups can be assigned through complementary NMR experiments. This method enables the identification and interrogation of the individual isomers in complex mixtures of cages which cannot be performed in solution. Furthermore, these techniques allow the stability of individual isomers within the mixture to be probed, with the T-symmetric isomers in this case shown to be more robust than the C 3 and S 4 analogues.

Ion Mobility Mass Spectrometry for Large Synthetic Molecules: Expanding the Analytical Toolbox

“…101 Recently, Mullen and co-workers separated the diastereomers of different {M 4 L 6 } coordination cages. 102 The separation of isomers and even enantiomers 103 is a particular interesting opportunity of IM-MS. While enantiomers cannot be separated directly using conventional IM, this can for example be accomplished via the formation of host−guest complexes with a chiral macrocyclic selector.…”

“…As early as 1990, using a drift-tube IM-MS instrument, Kemper and Bowers were able to separate the ground and excited state of Co + . Recently, Mullen and co-workers separated the diastereomers of different {M 4 L 6 } coordination cages …”