Multiple Pathways in the Self-Assembly Process of a Pd4L8 Coordination Tetrahedron.

The self-assembly of a Pd418 coordination tetrahedron (Tet) from a ditopic ligand, 1, and palladium(II) ions, [PdPy*4]2+ (Py* = 3-chloropyridine), was investigated by a 1H NMR-based quantitative approach (quantitative analysis of self-assembly process, QASAP), which allows one to monitor the average composition of the intermediates not observed by NMR spectroscopy. The self-assembly of Tet takes place mainly through three pathways and about half of the Tet structures were produced through the reaction of a kinetically produced Pd3L6 double-walled triangle (DWT) and 200-nm-sized large intermediates (IntL). In two of the three pathways, the leaving ligand (Py*), which is not a component of Tet, catalytically assisted the self-assembly. Such a multiplicity of the self-assembly process of Tet suggests that molecular self-assembly takes place on an energy landscape like a protein-folding funnel.