Chiral Self‐Discrimination and Guest Recognition in Helicene‐based Coordination Cages

Chiral, nano‐sized confinements play a major role for enantioselective recognition and reaction control in biological systems. Supramolecular self‐assembly gives access to artificial mimics with tunable sizes and properties. Here, a new family of [Pd2L4] coordination cages based on a chiral [6]helicene backbone is introduced. The racemic mixture of bis‐monodenate pyridyl ligand L1 assembles with PdII cations under chiral self‐discrimination selectively to an achiral meso cage cis‐[Pd2L1P2L1M2]. Enantiopure L1 forms homochiral cages [Pd2L1P/M4]. Longer derivative L2 forms chiral cages [Pd2L2P/M4] with larger cavities, able to bind optical isomers of chiral guests with different affinities. Owing to its distinct chiroptical properties, this cage can distinguish non‐chiral guests of different lengths, as they were found to squeeze or elongate the cavity under modulation of the helicenes' helical pitch. CD spectroscopic results are supported by ion mobility mass spectrometry. L2 was further found to yield a unique homochiral, interpenetrated double‐cage [Pd4L2P/M8], as supported by NMR, MS and single crystal X‐ray results.

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