Structural and Dynamic Aspects of Palladium(II)‐Based Self‐Assembled Binuclear Coordination Complexes

Mapping the Assembly of Neutral Tetrahedral Cages Tethered by Oximido Linkers and Their Guest Encapsulation Studies

A primary criterion for the design of polyhedral metal-organic cages is the requirement of geometrically matched pairs of metal ions and ligand moieties. However, understanding the pathway it takes to reach the final polyhedral structure can provide more insights into the self-assembly process and improved design strategies. In this regard, we report two neutral tetrahedral cages with the formulas {[Pd₃(NⁱPr)₃PO]₄(L¹)₆} (1-TD) and {[Pd₃(NⁱPr)₃PO]₄(L²)₆} (2-TD) starting from the acetate-bridged cluster {[Pd₃(NⁱPr)₃PO]₂(OAc)₂(OH)}₂·2(CH₃)₂SO (HEXA-Pd) and the respective oxamide precursors (L¹H₂: [C₂(NH₂)₂O₂]) and (L²H₂: (C₂(NHMe)₂O₂]). When subtle variations in the reaction conditions were made, two new tetrameric Pd₁₂ assemblies, {[Pd₃(NⁱPr)₃PO]₄(L¹)₂(OAc)₄(OMe)₄} (1-TM) and {[Pd₃(NⁱPr)₃PO]₄(L²)₂(OAc)₄(OMe)₄} (2-TM), were obtained from the same precursors. Detailed investigations using NMR, mass spectrometry, X-ray crystallography, and computational studies indicate that the macrocyclic complexes 1-TM and 2-TM are the reaction intermediates involved in the formation of the tetrahedral cages 1-TD and 2-TD, respectively. Moreover, the tetrahedral cages 1-TD and 2-TD exhibited intrinsic cavities of volume ∼85 ų. Guest encapsulation studies revealed that the cage 1-TD can encapsulate a wide range of guest molecules such as CH₂Cl₂, CHCl₃, CCl₄, C₆H₆, and C₆H₅F. Interestingly, 1-TD was shown to exhibit a preferential binding of C₆H₅F and C₆H₆ over other halogenated guest molecules, as determined from NMR titrations and computational studies.

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

The importance of the collaboration of experiment and theory has been proven in many examples in science and technology. Here, such a new example is shown in the investigation of molecular self-assembly process, which is a complicated multi-step chemical reaction occurring in the reaction network composed of a huge number of intermediates. An experimental method, QASAP (quantitative analysis of self-assembly process), developed by us and a numerical approach, NASAP (numerical analysis of self-assembly process), that analyzes the experimental data obtained by QASAP to draw detail molecular self-assembly pathways, which was also developed by us, are introduced, and their application to the investigation of Pd(II)-mediated coordination assemblies are presented. Further, the possibility of the prediction of the outcomes of molecular self-assembly by varying the reaction conditions is also demonstrated. Finally, a future direction in the field of artificial molecular self-assembly based on pathway-dependent self-assembly, that is, kinetic control of molecular self-assembly is discussed.