Ligand‐Directed Synthesis of a Self‐Organized Chloro‐Bridged Cubic Pd(II) Cage Showing Selective Encapsulation of Phenols

The synthesis and guest recognition properties of a neutral Pd24‐cubic cage, [{Pd3(NiPr)3PO}8(μ2‐Cl)24] 1 are reported. The formation of the cubical assembly takes place by an exclusive one‐pot ligand‐assisted pathway directed by an oximido linker. The initial coordination of the oximido ligand pre‐organizes the [Pd3(NiPr)3PO]3+ polyhedral building units into a tetrameric intermediate, which then transforms into an oximido‐tethered tetrahedral assembly and to the cubical cage 1 in the presence of chloride ions. In the absence of the directing oximido linker, no cage formation was observed, and the Pd6‐precursor was found to undergo self‐condensation, giving rise to a new pentameric polyhedral cluster, [Pd5{(NiPr)3PO}2(OAc)2(OH)2] 2. The central cavity of the cube has been probed for guest encapsulation studies, which shows a high binding with phenolic guest molecules with association constants of the order of 104–105 M−1. The favorable formation of host–guest complexes was attributed to the strong hydrogen bonding interactions between the host and guest functional groups. A stepwise formation of a metal‐chloride neutral cage has been shown to involve the initial pre‐organization of the Pd3 subunits of a Pd6‐hexamer mediated by a directional oxamide linker to a tetrameric Pd12 assembly followed by its conversion into a Pd12‐tetrahedron and finally to a chloro‐bridged Pd24 cube upon ligand substitution. The Pd24‐cube shows selective encapsulation of phenolic guest molecules.