Abstract
Subcomponent exchange transformed new high-spin FeII4L4 cage 1 into previously-reported low-spin FeII4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage’s FeII centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addition of p-anisidine to a mixture of high-spin 1 and previously-reported low-spin FeII4L6 cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addition of 2-formylpyridine to an identical mixture of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addition of 2-formylpyridine thus modulated the system’s behavior, fundamentally altering its response to the subsequent signal p-anisidine.
Highlights
Subcomponent exchange transformed new high-spin FeII4L4 cage 1 into previously-reported low-spin FeII4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage’s FeII centers
S timuli-responsive container molecules,[1] whose uptake and release of guests can be controlled through the application of external signals,[2] are useful building blocks for molecular networks.[3]
Structures prepared via subcomponent self-assembly[7] can transform in response to external stimuli through the reversible reconfiguration of the dynamic covalent and coordinative bonds holding the structures together;[8] examples include the rearrangements of a Schiff-base ligand7b and meso-helicates7e via aldehyde exchange, and the imine exchanges undergone by dynamic cages when an electron-rich amine substitutes an electron-poor amine residue.[9]
Summary
In addition to the encapsulated 1-FA within 2, a putative intermediate encapsulated 1-FA species was observed in the 19F NMR spectrum during equilibration (Figure S74), suggesting that the guest remained bound during the transformation. As p-anisidine (24 equiv) was progressively added, the 1H NMR signals corresponding to [1-FA ⊂ 1] were observed to disappear whereas those for [BF4− ⊂ 3] remained (Figures S88−S89). The addition of excess panisidine (24 equiv) to [1-FA ⊂ 1] resulted in its complete disassembly at room temperature in the presence of [BF4− ⊂ 3], releasing 1-FA (Figures S85−S87). The selectivity of cage disassembly was inverted for an equimolar mixture of [1-FA ⊂ 2] and [BF4− ⊂ 3] due to the increased thermodynamic stability of face-capped compared with edge-bridged tetrahedra;[24] only the NMR signals for [BF4− ⊂ 3] disappeared following progressive addition of panisidine (12 equiv) and heating (Figures S100−S101). S98), BF4−, resulting whereas in disassembly 1-FA remained of [BF4− ⊂ 3] and release of bound within the transformed cage 2 (Figure S99)
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