Pathway-Dependent Post-assembly Modification of an Anthracene-Edged MII^{II}4L6_4L_6 Tetrahedron

Fe$^{II}$$_4L_6$ tetrahedral cage $\textbf{1}$ undergoes post-assembly modification (PAM) via a Diels-Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage $\textbf{2}$ possesses an enclosed cavity suitable for encapsulation of the fullerene C$_{60}$, whereas original cage $\textbf{1}$ forms a unique covalent adduct through a Diels-Alder cycloaddition of three of its anthracene ligands with C$_{60}$. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C$_{60}$ and TCNE. Modified cage $\textbf{2}$ was also able to bind an anionic guest, [Co(C$_2$B$_9$H$_{11}$)$_2$]$^{-}$, which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts.Engineering and Physical Sciences Research Council, University of Cambridge (Herchel Smith Research Fellowship), Corpus Christi College (Cambridge; Fellowship

Anion Binding in Water Drives Structural Adaptation in an Azaphosphatrane-Functionalized Fe(II)4L4 Tetrahedron

Anion-templated aqueous self-assembly resulted in the formation of an endohedrally functionalized Fe$^\text{II}$$_{4}$L$_4$ tetrahedron from azaphosphatrane-based subcomponents. This new water-soluble cage is flexible and able to encapsulate anions with volumes ranging from 35 to 219 Å$^3$ via hydrogen bonding and electrostatic interactions. It structurally adapts in response to the size and shape of the template anions, dynamically adopting a conformation either where all four azaphosphatrane $^{+}$P-H vectors point inward, or else where one points outward and the other three inward. The two cage isomers can coexist in solution and interconvert. A shape memory phenomenon was observed during guest displacement because guest exchange occurs more rapidly than structural reconfiguration.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC EP/M008258/1). The authors thank the Department of Chemistry NMR facility, University of Cambridge for performing some NMR experiments, and the EPSRC UK National Mass Spectrometry Facility at Swansea University for carrying out high-resolution mass spectrometry. D.Z. acknowledges a grant from the China Scholarship Council, Accueil Doc Bursary from France RhôneAlpes Region, and Enveloppe AttractivitéFellowship from ENSLyon for Ph.D. studies

Metallo-cryptophane cages from cis-linked and trans-linked strategies

Trigonal bipyramidal metallo-cage species [Pd₃(dppp)₃(L)₂]∙6OTf (where dppp = bis(diphenylphosphino)propane, OTf = triflate and L is tris(iso-nicotinoyl)cyclotriguaiacylene (L1) or tris(fluoro-iso-nicotinoyl)cyclotriguaiacylene (FL1)) have been characterised in solution to exist predominantly as the anti-isomers. The crystal structure of [Pd₃(dppp)₃(FL1)₂]∙6OTf, however, was found to be the achiral syn-isomer. The complex [Pd₃Cl₃(L2)₂] (where L2 = tris(methylbenzimidazolyl)cyclotriguaiacylene) is a trans-linked M₃L₂ cage, observed by mass spectrometry and in the solid state as the anti-isomer. Ligand L2 also forms a 1:1 co-crystal with cyclotriguaiacylene

Signal transduction in a covalent post-assembly modification cascade

Natural reaction cascades control the movement of biomolecules between cellular compartments. Inspired by these systems, we report a synthetic reaction cascade employing post-assembly modification reactions to direct the partitioning of supramolecular complexes between phases. The system is composed of a self-assembled tetrazine-edged FeII8L12 cube and a maleimide-functionalized FeII4L6 tetrahedron. Norbornadiene (NBD) functions as the stimulus that triggers the cascade, beginning with the inverse-electron-demand Diels–Alder reaction of NBD with the tetrazine moieties of the cube. This reaction generates cyclopentadiene as a transient by-product, acting as a relay signal that subsequently undergoes a Diels–Alder reaction with the maleimide-functionalized tetrahedron. Cyclooctyne can selectively inhibit the cascade by outcompeting NBD as the initial trigger. Initiating the cascade with 2-octadecyl NBD leads to selective alkylation of the tetrahedron upon cascade completion. The increased lipophilicity of the C18-tagged tetrahedron drives this complex into a non-polar phase, allowing its isolation from the initially inseparable mixture of complexes

Reticular synthesis of porous molecular 1D nanotubes and 3D networks

Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal–organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of ‘reticular synthesis’, in which multiple building blocks can be assembled according to a common assembly motif. Here we apply a chiral recognition strategy to a new family of tubular covalent cages to create both 1D porous nanotubes and 3D diamondoid pillared porous networks. The diamondoid networks are analogous to MOFs prepared from tetrahedral metal nodes and linear ditopic organic linkers. The crystal structures can be rationalized by computational lattice-energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the ‘node and strut’ principles of reticular synthesis to molecular crystals

Lanthanide coordination polymers with pyridyl-N-oxide or carboxylate functionalised host ligands

The first examples of coordination polymers of hard-donor functionalised cyclotriveratrylene ligands with the lanthanide(iii) cations are reported, these include 1D 3-connected ladder structures and a 2D decorated kagome dual

Dynamic optimization of guest binding in a library of diastereomeric heteroleptic coordination cages

Biological receptors such as enzymes are highly flexible and alter their conformation to fit target substrates. Synthetic supramolecular hosts such as coordination cages also exhibit some ability to adapt their cavity shape and size in response to guest molecules, due to the dynamic nature of the linkages that hold them together. Here we report the preparation of a new trigonal-prismatic coordination cage that forms selectively, incorporating two different ligands. The cage exhibits up to four diastereomeric configurations, differing in the ‘portrait’ or ‘landscape’ orientation of tetratopic pyrene-based ligands on its rectangular faces. Three diastereomeric forms of the cage have been structurally characterised, and NMR spectroscopy confirmed the formation of a mixture of diastereomers in solution. Although the cage panels are rigid, the different orientations that each panel can adopt enables the cage cavity to dynamically adapt to optimize the binding of guests including elongated adamantane derivatives and toxic organochlorine pesticides