Identification of a Heteroleptic PdLL' Coordination Cage by Screening of a Virtual Combinatorial Library.

The design of structurally defined heteroleptic coordination cages is a challenging task, and only few examples are known to date. Here we describe a selection approach that allowed the identification of a novel hexanuclear Pd cage containing two types of dipyridyl ligands. A virtual combinatorial library of PdL complexes was prepared by mixing six different dipyridyl ligands with substoichiometric amounts of Pd(CHCN). Analysis of the equilibrated reaction mixture revealed the preferential formation of a heteroleptic PdLL' assembly. The complex was prepared on a preparative scale by a targeted synthesis, and its structure was elucidated by single-crystal X-ray diffraction. It features an unprecedented trigonal-antiprismatic cage structure with two triangular PdL macrocycles bridged by six L' ligands. A related but significantly larger PdLL' cage was obtained by using metalloligands instead of organic dipyridyl ligands.