Navigated Self-Assembly of a Pd₂L₄ Cage by Modulation of an Energy Landscape under Kinetic Control

Abstract

Kinetic control of molecular self-assembly remains difficult because of insufficient understanding of molecular selfassembly mechanism. Here we report the formation of a metastable [Pd2L4] 4+ cage structure composed of naphthalene-based ditopic ligands (L) and Pd(II) ions in very high yield (99%) under kinetic control by modulating the energy landscape. The guest anion trapped in the cage and the solvent with very weak coordination ability prefer the formation of suitable intermediates and prevent the conversion of the metastable cage into the thermodynamically most stable decomposed state. The cage formation pathways under kinetic control and the effect of the anions encapsulated on the self-assembly processes were investigated by QASAP (quantitative analysis of self-assembly process) and NASAP (numerical analysis of self-assembly process). It was found that the self-assembly with a preferred guest (BF4-) proceeds through intermediates composed of no more components than the cage ([PdaLbXc] 2a+ (a ≤ 2, b ≤ 4, X indicates a leaving ligand)) and that the final intramolecular cage-closure step is the rate-determining step. In contrast, a weaker guest (OTf-) causes the transient formation of intermediates composed of more components than the cage ([PdaLbXc] 2a+ (a > 2, b > 4)), which are finally converted into the cage.

Inducing Social Self‐Sorting in Organic Cages To Tune The Shape of The Internal Cavity

“…We previously used density functional theory (DFT) formation energies to explain the thermodynamically preferred cage topologies in the dynamic imine-based selfassembly processes. [41,[57][58][59] Comparing the thermodynamic stabilities of potential cage products can be ag ood guide to selectivity,b ut the reaction outcome can also be affected by factors,s uch as reaction kinetics, [39,[60][61][62][63][64] solvent effects, [65][66][67][68] and the solubilities of the species involved in the equilibrium. [33,40,47] In parallel with the synthetic efforts,w eu sed computational techniques to predict the stability of the different homo-and heteroleptic structures originating from aldehydes B1-B2 and L1-L4.T he experimentally observed outcomes agreed with the relative gas-phase formation energies of the possible Tet 3 Di 6 products,s howing the predictive power of the simple model for the self-sorting behaviour of imine-based organic cages.…”

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

“…NASAP for the (BF 4 − ) [Pd 2 4 4 ] 4+ cage assembly in the same reaction network model with five reaction types used for the (NO 3 − ) [Pd 2 3 4 ] 4+ cage (Figures 9a and 11c) showed that the rate constant of the final crosslinking ( k 5 ) is the smallest among the three intramolecular reactions ( k 3 , k 4 , and k 5 ), which is the same as seen in the [Pd 2 2 4 ] 4+ and the (NO 3 − ) [Pd 2 3 4 ] 4+ cages (Figure 12b) [16] . However, k 3 and k 4 for the (BF 4 − ) [Pd 2 4 4 ] 4+ cage are much smaller than those for the (NO 3 − ) [Pd 2 3 4 ] 4+ cage, indicating that more flexible ditopic ligand 3 is more advantageous for the cyclization probably due to the preferential formation of the distorted transition structure and intermediate of the cyclization, where one of the Pd(II) ions has to adopt five‐coordinate geometry [9]…”

“…Recently, it was found that a metastable Pd 2 L 4 cage can be prepared under the QASAP condition [16] . The ditopic ligand 4 gave [Pd 2 4 4 ] 4+ cage only when a good template anion such as BF 4 − is present in the reaction mixture (Figure 12a).…”

Light-induced assembly and disassembly of polymers with PdnL2n-type network junctions

“…On the other hand, the donor strength of the ligand can be compensated by other factors ( e.g. anion effects), 23 as evidenced by the higher G ′ value of P1 when compared to what is found for P2 .…”