Bifurcation of self-assembly pathways to sheet or cage controlled by kinetic template effect

Abstract

The template effect is a key feature to control the arrangement of building blocks in assemblies, but its kinetic nature remains elusive compared to the thermodynamic aspects, with the exception of very simple reactions. Here we report a kinetic template effect in a selfassembled cage composed of flexible ditopic ligands and Pd(II) ions. Without template anion, a micrometer-sized sheet is kinetically trapped (off-pathway), which is converted into the thermodynamically most stable cage by the template anion. When the template anion is present from the start, the cage is selectively produced by the preferential cyclization of a dinuclear intermediate (on-pathway). Quantitative and numerical analyses of the selfassembly of the cage on the on-pathway revealed that the accelerating effect of the template is stronger for the early stage reactions of the self-assembly than for the final cage formation step itself, indicating the kinetic template effect.

Coordination Self‐Assembly Processes Revealed by Collaboration of Experiment and Theory: Toward Kinetic Control of Molecular Self‐Assembly

“…By screening of counter anions, it was found that NO 3 − is strongly bound in the cavity of the cage and that when the self‐assembly of the (NO 3 − ) [Pd 2 3 4 ] 4+ cage was conducted in the presence of NO 3 − , the sheet formation was prevented to give the cage in high yield. The template effect of NO 3 − was confirmed by the acceleration of the macrocyclization in the model complex, [ Pd 2 3 2 ] 4+ , from [ Pd Py* 2 ](BArF) 2 ( Pd indicates Pd(TMEDA) and BArF indicates [{3,5‐(CF 3 ) 2 C 6 H 3 } 4 B]) and 3 in the presence of NO 3 − (Figure 11a) [15b] . Note that NO 3 − has high enough coordination ability to promote ligand exchange of coordination bonds, which may also contribute to the acceleration of the formation of the (NO 3 − ) [Pd 2 3 4 ] 4+ cage.…”

“…When the self‐assembly of the [Pd 2 3 4 ] 4+ cage was carried out with OTf − as the counter anion, the cage formation was dramatically retarded, [15b] suggesting that the counter anion affects the self‐assembly of the cage. It was found that the size of the kinetically produced sheet from [PdPy* 4 ](OTf) 2 and 3 is micrometer‐sized much larger than the size of the sheet prepared with BF 4 − and that the sheet was converted into the cage by the addition of BF 4 − , which indicates that the templation of the counter anion also contributes to the conversion of the sheet into the cage (Figure 11a).…”

“…The self‐assembly process of the (NO 3 − ) [Pd 2 3 4 ] 4+ cage was investigated by NASAP (Figure 11b) [15b] . In order to discuss the rate constants of the three types of intramolecular reactions to form the cage, all the elementary reactions in the network of the Pd 2 L 4 cage are classified into five groups shown in Figure 11c.…”

Coordination/Metal–Organic Cages Inside Out

“…8i, middle) [79]. A solution study of CCs with flexible ligands also revealed that the encapsulation of appropriate anions is essential to selectively obtain a lantern structure over undesired polymerized products [239].…”

Unexpected Self-Assembly Pathway to a Pd(II) Coordination Square-Based Pyramid and Its Preferential Formation beyond the Boltzmann Distribution

“…Molecular self-assembly is a phenomenon where building blocks assemble into a well-defined structure based on their intermolecular interactions and is a fundamental strategy to fabricate functional units and materials in biological and abiotic systems. − The self-assembly mechanism − is one of the research topics in molecular self-assembly because it is mysterious that the building blocks spontaneously assemble into an ordered structure as if they had intention and because the understanding of assembly mechanisms will make it possible to obtain novel assemblies that are inaccessible under thermodynamic control. − Coordination self-assemblies are constructed by reversible coordination bonds that are made between organic multitopic ligands and metal ions. − As their structures are simple compared to biological molecular self-assemblies, coordination self-assemblies are suitable models for the investigation of the self-assembly mechanism.…”