Selective Construction of Very Large Stacking-Interaction-Induced Molecular 8₁₈ Metalla-knots and Borromean Ring Using Curved Dipyridyl Ligands

Abstract

Two molecular metalla-knots containing over 500 non-hydrogen atoms (especially 16 RhIII ions) and one molecular Borromean ring were obtained in high yields facilitated by multiple intermolecular interactions between their components. The syntheses rely on the strategic selection of the nonlinear dipyridyl ligand 2,7-di­(pyridin-4-yl)-9H-fluorene (L 1 ) as precursor, and the structures of the assemblies were confirmed by detailed X-ray crystallographic analysis. Subsequently, replacing L 1 with the bulkier ligand 4,4′-(9,9-dimethyl-9H-fluorene-2,7-diyl)­dipyridine (L 2 ) led to the formation of three tetranuclear metallocycles in high yields on account of the weakened π–π stacking interactions between the naphthacene/anthracene and fluorene moieties, which in turn confirmed the significance of stacking interactions in the construction of the molecular 818 metalla-knots and the molecular Borromean ring.

Integrative Assembly of Heteroleptic Tetrahedra Controlled by Backbone Steric Bulk

“…A similar backbone design was reported to lead to Fe-based helicates and tetrahedra, 57 − 60 as well as knots and Borromean rings. 61 …”

Selective Construction of Trefoil knots and a Molecular Borromean Ring Induced by Steric Hindrance of Thioether Ligands

“…Recently, our group reported the selective construction of molecular 8 18 metalla‐knots and a Borromean ring using curved dipyridyl ligands, and we found that increasing the steric hindrance of the dipyridyl ligand can weaken π−π stacking interactions, leading instead to the formation of simple tetranuclear metallacycles [39] . This work inspired us to envision whether replacing smaller ligands with bulkier ligands could give rise to more complex structural changes rather than merely the formation of simple monocyclic compounds.…”

“…[3,15,[20][21][22][23][24][25] As a complementary method to template-based syntheses, coordination-driven self-assembly has become an essential -and in many ways advantageous -approach to the high-yielding construction of a range of molecular metalla-knots and -links over the last decade. [4,14,15,23,[26][27][28][29][30][31][32] Focusing on the latter approach, our group has taken advantage of half-sandwich organometallic fragments together with ligands having different geometrical characteristics to construct a family of molecular metalla-knots and -links featuring complex and exquisite topologies, [30,[33][34][35][36][37][38][39] in addition to exploring their applications in the separation of halogenated aromatics [40] and stimuli-responsive topological transformations. [41][42][43] Recently, our group reported the selective construction of molecular 8 18 metalla-knots and a Borromean ring using curved dipyridyl ligands, and we found that increasing the steric hindrance of the dipyridyl ligand can weaken πÀ π stacking interactions, leading instead to the formation of simple tetranuclear metallacycles.…”

“…[41][42][43] Recently, our group reported the selective construction of molecular 8 18 metalla-knots and a Borromean ring using curved dipyridyl ligands, and we found that increasing the steric hindrance of the dipyridyl ligand can weaken πÀ π stacking interactions, leading instead to the formation of simple tetranuclear metallacycles. [39] This work inspired us to envision whether replacing smaller ligands with bulkier ligands could give rise to more complex structural changes rather than merely the formation of simple monocyclic compounds. To this end, we chose ligand L 1 and the bulkier ligand L 2 as comparisons (Scheme 1), together with polydentate ligands H 2 À CA and H 2 À TtDo, respectively, to construct supramolecular organometallic compounds, with the help of Cp*Rh III metal corner units, to determine if the bulkier ligand could drive the generation of compounds with other sophisticated topologies.…”

“…Focusing on the latter approach, our group has taken advantage of half‐sandwich organometallic fragments together with ligands having different geometrical characteristics to construct a family of molecular metalla‐knots and ‐links featuring complex and exquisite topologies, [30,33–39] in addition to exploring their applications in the separation of halogenated aromatics [40] and stimuli‐responsive topological transformations [41–43] …”