Self-Assembled Hexanuclear Organometallic Cages: Synthesis, Characterization, and Host-Guest Properties

A series of iridium- and rhodium-based hexanuclear organometallic cages containing 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone, 9,10-dihydroxy-1,4-anthraquinone, and 6,11-dihydroxynaphthacene-5,12-dione ligands were synthesized from the self-assembly of the corresponding molecular clips and 2,4,6-tri(4-pyridyl)-1,3,5-triazine ligands in good yields. These organometallic cages can form inclusion systems with a wide variety of p-donor substrates, including coronene, pyrene, [Pt(acac)2], and hexamethoxytriphenylene. The 1:1 complexation of the resulting supramolecular assemblies was confirmed by 1H NMR spectroscopy. Large complexation shifts (?d>1 ppm) were observed in the 1H NMR spectra of guests in the presence of cage [Cp*6M6(mu-DHNA)3(tpt)2](OTf)6 (6?a; M=Ir, tpt=2,4,6-tri(4-pyridyl)-1,3,5-triazine). The formation of discrete 1:1 donoracceptor complexes, pyrene?6?b (M=Rh), coronene?6?a, coronene?6?b, and [Pt(acac)2]?6?a was confirmed by their single-crystal X-ray analyses. In these systems, the most important driving force for the formation of guesthost complexes is clearly the donoracceptor p...p stacking interaction, including charge-transfer interactions between the electron-donating and electron-accepting aromatic components. These structures provide compelling evidence for the existence of strong attractive forces between the electron-deficient triazine core and electron-rich guest. The results presented here may provide useful guidance for designing artificial receptors for functional biomolecules.