Topological prediction of palladium coordination cages

Abstract

The preparation of functionalized, heteroleptic Pd _<i>x</i> L_2<i>x</i> coordination cages is desirable for catalytic and optoelectronic applications. Current rational design of these cages uses the angle between metal-binding (∠<i>B</i>) sites of the di(pyridyl)arene linker to predict the topology of homoleptic cages obtained <i>via</i> non-covalent chemistry. However, this model neglects the contributions of steric bulk between the pyridyl residues-a prerequisite for endohedrally functionalized cages, and fails to rationalize heteroleptic cages. We describe a classical mechanics (CM) approach to predict the topological outcomes of Pd _<i>x</i> L_2<i>x</i> coordination cage formation with arbitrary linker combinations, accounting for the electronic effects of coordination and steric effects of linker structure. Initial validation of our CM method with reported homoleptic Pd₁₂ <b>LFu</b> ₂₄ (<b>LFu</b> = 2,5-bis(pyridyl)furan) assembly suggested the formation of a minor topology Pd₁₅ <b>LFu</b> ₃₀, identified experimentally by mass spectrometry. Application to heteroleptic cage systems employing mixtures of <b>LFu</b> (∠<i>B</i> = 127°) and its thiophene congener <b>LTh</b> (∠<i>B</i> = 149° ∠<i>B</i> _exp = 152.4°) enabled prediction of Pd₁₂L₂₄ and Pd₂₄L₄₈ coordination cages formation, reliably emulating experimental data. Finally, the topological outcome for exohedrally (<b>LEx</b>) and endohedrally (<b>LEn</b>) functionalized heteroleptic Pd _<i>x</i> L_2<i>x</i> coordination cages were predicted to assess the effect of steric bulk on both topological outcomes and coordination cage yields, with comparisons drawn to experimental data.