NiII–PdII as a More Solution-Stable Paddlewheel Alternative to CuII–CuII in Metal–Organic Cages

The dinuclear CuII-carboxylate paddlewheel is a lynchpin of metal–organic cages (MOCs), yet has been shown to be highly labile in solution. Herein, kinetically stable heterometallic (NiPd)2L4 lantern-type helicate cages have been assembled from preformed [NiPd(OAc)4] paddlewheel precursor complexes. Ligand exchange experiments followed by HPLC revealed the half-lives of the (NiPd)2L4 cages in solution to be 103 times greater than that of Cu4L4 cage analogues. Due to the unique non-coordinating, charge-neutral PdII···PdII cavity, the hydrophobic guest chloranil was encapsulated inside a (NiPd)2L4 cage with no evidence of guest uptake in the presence of the analogous Cu4L4 cage. The NiII–PdII paddlewheel system provides a kinetically stable yet synthetically accessible alternative to labile CuII-based metallosupramolecular cages with cavities unoccupied by coordinating solvent molecules or counterions.