Self‐Assembly of a Pd4L8 Double‐Walled Square Partly Takes Place Through the Formation of Kinetically Trapped Species

Abstract

We investigated the self‐assembly process of a Pd4L8 double‐walled square (DWS) from [PdPy*4]2+ (Py*: 3‐chloropyridine used as the leaving ligand on the PdII center) and an organic ditopic ligand by QASAP (quantitative analysis of self‐assembly process). DWS is assembled mainly through three pathways. Within 5 minutes of the self‐assembly, all of the substrates, the metal source and the organic ditopic ligand, were completely consumed and converted into primary intermediates. In 2 h, the primary intermediates afforded 30 % of DWS, 200‐nm‐sized large intermediates, and a relatively stable transient intermediate. This stable intermediate was characterized as a kinetically trapped Pd3L6 double‐walled triangle (DWT) by NMR and mass measurements. From 2 h to 1 day, 19 % of DWS was formed from the 200‐nm‐sized large intermediate with the aid of Py*, which is not a component of the final assembly. After 1 day, the remaining large intermediate and DWT afforded 39 % of DWS with the aid of Py* again. This self‐assembly process is quite different from that of previously reported single‐walled macrocycles, and the change in the self‐assembly pathway would arise from the difference in the flexibility of ditopic ligands. This study revealed a complicated multiplicity, not a simple single pathway, of the self‐assembly process of DWS.