Dynamic Self‐Assembly of an M₃L₆ Molecular Triangle and an M₄L₈ Tetrahedron from Naked Pd^II Ions and Bis(3‐pyridyl)‐Substituted Arenes

Abstract

The pyridine-appended nonchelating bidentate ligands 1,4-bis(3-pyridyl)benzene (1) and 4,4'-bis(3-pyridyl) biphenyl (2) were complexed with a naked Pd(II) ion for the construction of molecular cage compounds. Prior to these experiments, the complexation of the ligands with cis-[Pd(en)(NO3)2] was also examined, because self-assemblies from the cis-protected Pd(II) ion were expected to be simple motifs that constitute the assemblies from naked Pd(II) ion. The structures of the self-assembled compounds resulting from 1 and [Pd(en)(NO3)2] depended on the solvent employed. In aqueous solution, an M2L2 trenchlike compound was obtained. In dimethyl sulfoxide, however, a mixture of the M2L2 trench and an M3L3 macrocycle was found in equilibrium, the dynamic nature of which was confirmed by the concentration-dependent nature of the species. At higher concentration, an M4L4 macrocycle was mostly observed. The complexation of 1 with naked Pd(II) ions was expected to produce novel structures that are combinations of the M(n)L(n) type frameworks. A peculiar tetrahedral M4L8 assembly was obtained quantitatively from 1 and Pd(NO3)2, rather than the smallest possible M3L6 double-walled triangle. Interestingly, the use of Pd(CF3SO3)2 resulted in the sole formation of the latter structure. Thus, the anion is important as a template in the formation of these assemblies. Ligand 2, which contains an extra p-phenylene unit compared to 1, behaved in a similar manner when treated with [Pd(en)(NO3)2], but showed subtle differences with naked Pd(II) ions. With Pd(NO3)2, 2 gave mostly a tetrahedron along with a double-walled triangle. With Pd(CF3SO3)2, this longer ligand formed a double-walled triangle with a negligible amount of tetrahedra. A single discrete assembly of a perfect tetrahedron was obtained from 2 and Pd(II) ions by choosing p-tosylate as a counterion.

A New Structural Motif for an Enantiomerically Pure Metallosupramolecular Pd4L8 Aggregate by Anion Templating

“…These are shown in Figure 1: The first is a crown-like metallamacrocycle in which two ligands bridge two metal centers. [5] This kind of assembly is even more rare, and in fact only a single ligand with a very rigid linear backbone and two 3-pyridyl units has been reported to form this type of structure upon coordination to tetravalent palladium(II) ions. Synthesis of the axially chiral ligand 1. of 3-pyridyl groups yet described.…”

“…The second has a tetrahedron-like arrangement of the metal ions in which two of the six edges of the tetrahedron are doubly bridged by two ligands, whereas the other four are only singly bridged by a single ligand. [5] This kind of assembly is even more rare, and in fact only a single ligand with a very rigid linear backbone and two 3-pyridyl units has been reported to form this type of structure upon coordination to tetravalent palladium(II) ions. Finally, a catenated structure has been reported in which two M 2 L 4 cages are interlocked into each other.…”

Solvent-dependent Assembly of Discrete and Continuous CoCl2 Adamantane-based Ligand Complexes: Observations by CSI–Mass Spectrometry and X-ray Crystallography

“…Significant attention has recently been given to coordination chemistry, which has found applications in the construction of complicated or nano-sized structures, catenanes, 1,2 rotaxanes, [3][4][5] helices, 6,7 molecular squares, [8][9][10] tetrahedral hosts, [11][12][13][14][15][16] and so on. [17][18][19][20][21] Coordination compounds exist not only as discrete molecules in solution, but also as compounds with infinite periodicity in the crystal state.…”

Self‐Assembly Processes of Pd(II)‐ and Pt(II)‐Linked Discrete Self‐Assemblies Revealed by QASAP

“…The formation of a Pd 4 5 8 tetrahedron ( Tet ) also took place through multiple pathways (Figure ) . In this case, a mixture of primitive intermediates ( Int P ) that are smaller than the final self‐assembly were produced in the very early stage of the self‐assembly (stage I).…”