Abstract
Fullerenes and their derivatives are of tremendous technological relevance. Synthetic access and application are still hampered by tedious purification protocols, peculiar solubility, and limited control over regioselective derivatization. We present a modular self-assembly system based on a new low-molecular-weight binding motif, appended by two palladium(II)-coordinating units of different steric demands, to either form a [Pd2L14]4+ cage or an unprecedented [Pd2L23(MeCN)2]4+ bowl (with L1 = pyridyl, L2 = quinolinyl donors). The former was used as a selective induced-fit receptor for C60. The latter, owing to its more open structure, also allows binding of C70 and fullerene derivatives. By exposing only a fraction of the bound guests’ surface, the bowl acts as fullerene protecting group to control functionalization, as demonstrated by exclusive monoaddition of anthracene. In a hierarchical manner, sterically low-demanding dicarboxylates were found to bridge pairs of bowls into pill-shaped dimers, able to host two fullerenes. The hosts allow transferring bound fullerenes into a variety of organic solvents, extending the scope of possible derivatization and processing methodologies.
Highlights
As stable carbon allotropes, fullerenes feature curved, fully πconjugated surfaces with unique electronic properties that render them highly versatile for application in functional materials.[1]
Within the field of supramolecular chemistry, large efforts have been devoted to the construction of fullerene receptors aimed at facilitating selective purification and derivatization methods.[3]
Straightforward conversion into ligands L1 and L2 was achieved by reaction with 3-aminopyridine and 6-aminoquinoline, respectively
Summary
Fullerenes feature curved, fully πconjugated surfaces with unique electronic properties that render them highly versatile for application in functional materials.[1]. The bowl’s sterically congested coordination environment allows clean conversion into a heteroleptic assembly[11] via hierarchical reaction with bridging carboxylates,8c,12 yielding a pill-shaped dimer, capable of binding two fullerenes.[13] All findings are supported by NMR and mass spectrometric results as well as single crystal X-ray structures of one ligand, both empty hosts, and three different host−guest complexes, achieved with a combination of cryogenic crystal handling, the use of highly brilliant synchrotron radiation,[14] and advanced macromolecular refinement protocols. 1H−1H NOESY NMR spectrum (Figure S15), the quinoline moieties’ 1H signal splitting into two sets with 2:1 integral ratio and the observation of prominent peaks in the ESI mass spectrum consistent with the formula [Pd2L23(MeCN)2]4+, alongside further + X]3+ (X = F−, Cadl−d,uBcFts4−w)i.thSuvrapriroisuins galnyi,osnlosw[Pvda2pLo2r3(dMiffeuCsiNon) of isopropyl ether into a MeCN solution of bowl [Pd2L23(MeCN)2]4+ produced single crystals for which a synchrotron-based diffraction experiment revealed the structure of cage [Pd2L24]4+ (Figure 4d), indicating the fine energetic balance between these two species. Analogous NMR and MS results were obtained for the guest-free (Figure S53−57) and (C70)2containing (Figure S64−69) dimers, showing that guest encapsulation is orthogonal to the dimerization process
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