Mechanically
interlocked molecules (MIMs) possess unique architectures
and nontraditional degrees of freedom that arise from well-defined
topologies that are achieved through precise mechanical bonding. Incorporation
of MIMs into materials can thus provide an avenue to discover new
and emergent macroscale properties. Here, the synthesis of a phenanthroline-based
[2]catenane crosslinker and its incorporation into polyacrylate organogels
are described. Specifically, Cu(I) metalation and demetalation was
used as a postgelation strategy to tune the mechanical properties
of a gel by controlling the conformational motions of integrated MIMs.
The organogels were prepared via thermally initiated free radical
polymerization, and Cu(I) metal was added in MeOH to the pretreated,
swollen gels. Demetalation of the gels was achieved by adding lithium
cyanide and washing the gels. Changes in Young’s and shear
moduli, as well as tensile strength, were quantified through oscillatory
shear rheology and tensile testing. The reported approach provides
a general method for postgelation tuning of mechanical properties
using metals and well-defined catenane topologies as part of a gel
network architecture.
Catenanes are a well-known class of mechanically interlocked
molecules
that possess chain-like architectures and have been investigated for
decades as molecular machines and switches. However, the synthesis
of higher-order catenanes with multiple, linearly interlocked molecular
rings has been greatly impeded by the generation of unwanted oligomeric
byproducts and figure-of-eight topologies that compete with productive
ring closings. Here, we report two general strategies for the synthesis
of oligo[n]catenanes that rely on a molecular “zip-tie”
strategy, where the “zip-tie” is a central core macrocycle
precursor bearing two phenanthroline (phen) ligands to make odd-numbered
oligo[n]catenanes, or a preformed asymmetric iron(II)
complex consisting of two macrocycle precursors bearing phen and terpyridine
ligands to make even-numbered oligo[n]catenanes.
In either case, preformed macrocycles or [2]catenanes are threaded
onto the central “zip-tie” core using metal templation
prior to ring-closing metathesis (RCM) reactions that generate several
mechanical bonds in one pot. Using these synthetic strategies, a family
of well-defined linear oligo[n]catenanes were synthesized,
where n = 2, 3, 4, 5, or 6 interlocked molecular
rings, and n = 6 represents the highest number of
linearly interlocked rings reported to date for any isolated unimolecular oligo[n]catenane.
We demonstrate the synthesis and characterization of a new class of late transition metal-aluminum heterobimetallic complexes. A bridging ligand which both chelates the transition metal and binds the aluminum via an alkoxide was employed to impart stability to the bimetallic system.
Mechanically interlocked molecules (MIMs) possess unique architectures and non-traditional degrees of freedom that arise from well-defined topologies that are achieved through precise mechanical bonding. Incorporation of MIMs into materials can thus provide an avenue to discover new and emergent macroscale properties. Here, the synthesis of a phenanthroline-based [2]catenane crosslinker and its incorporation into polyacrylate organogels is described. Specifically, Cu(I) metalation and de-metalation was used as a post-gelation strategy to tune the mechanical properties of a gel by controlling the conformational motions of integrated MIMs. The organogels were prepared via thermally initiated free radical polymerization, and Cu(I) metal was added in MeOH to pre-treated, swollen gels. De-metalation of the gels was achieved by adding cyanide salts and washing the gels. Changes in Young’s and shear moduli, as well as tensile strength, were quantified through oscillatory shear rheology and tensile testing. The reported approach provides a general method for post-gelation tuning of mechanical properties using metals and well-defined catenane topologies as part of a network architecture.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.