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Instruments / Technical Area	Publication Details	Published
I19-Small Molecule Single Crystal Diffraction	Transamidation-driven molecular pumps Lorna Binks , Chong Tian , Stephen D. P. Fielden , Iñigo J. Vitorica-Yrezabal , David A. Leigh Journal Of The American Chemical Society DOI: 10.1021/jacs.2c06807 Diamond Proposal Number(s): [23480] Open Access Show Abstract ▼ Abstract: We report a new class of synthetic molecular pumps that use a stepwise information ratchet mechanism to achieve the kinetic gating required to sequester their macrocyclic substrates from bulk solution. Threading occurs as a result of active template reactions between the pump terminus amine and an acyl electrophile, whereby the bond-forming reaction is accelerated through the cavity of a crown ether. Carboxylation of the resulting amide results in displacement of the ring to the collection region of the thread. Conversion of the carbamate to a phenolic ester provides an intermediate rotaxane suitable for further pumping cycles. In this way rings can be ratcheted onto a thread from one or both ends of appropriately designed molecular pumps. Each pumping cycle results in one additional ring being added to the thread per terminus acyl group. The absence of pseudorotaxane states ensures that no dethreading of intermediates occurs during the pump operation. This facilitates the loading of different macrocycles in any chosen sequence, illustrated by the pump-mediated synthesis of a [4]rotaxane containing three different macrocycles as a single sequence isomer. A [5]rotaxane synthesized using a dual-opening transamidation pump was structurally characterized by single-crystal X-ray diffraction, revealing a series of stabilizing CH···O interactions between the crown ethers and the polyethylene glycol catchment region of the thread.	Aug 2022
I19-Small Molecule Single Crystal Diffraction	A molecular endless (74) knot David Leigh , Jonathan J. Danon , Stephen D. P. Fielden , Jean-Francois Lemonnier , George F. S. Whitehead , Steffen L. Woltering Nature Chemistry 56 DOI: 10.1038/s41557-020-00594-x Diamond Proposal Number(s): [17379] Show Abstract ▼ Abstract: Current strategies for the synthesis of molecular knots focus on twisting, folding and/or threading molecular building blocks. Here we report that Zn(II) or Fe(II) ions can be used to weave ligand strands to form a woven 3 × 3 molecular grid. We found that the process requires tetrafluoroborate anions to template the assembly of the interwoven grid by binding within the square cavities formed between the metal-coordinated criss-crossed ligands. The strand ends of the grid can subsequently be joined through within-grid alkene metathesis reactions to form a topologically trivial macrocycle (unknot), a doubly interlocked [2]catenane (Solomon link) and a knot with seven crossings in a 258-atom-long closed loop. This 74 knot topology corresponds to that of an endless knot, which is a basic motif of Celtic interlace, the smallest Chinese knot and one of the eight auspicious symbols of Buddhism and Hinduism. The weaving of molecular strands within a discrete layer by anion-template metal–ion coordination opens the way for the synthesis of other molecular knot topologies and to woven polymer materials.	Dec 2020
I19-Small Molecule Single Crystal Diffraction	Single-step enantioselective synthesis of mechanically planar chiral [2]rotaxanes using a chiral leaving group strategy Chong Tian , Stephen D. P. Fielden , Borja Pérez-Saavedra , Iñigo J. Vitorica-Yrezabal , David Leigh Journal Of The American Chemical Society DOI: 10.1021/jacs.0c03447 Open Access Show Abstract ▼ Abstract: We report a one-step enantioselective synthesis of mechanically planar chiral [2]rotaxanes. Previous studies of such molecules have generally involved the separation of enantiomers from racemic mixtures or the preparation and separation of diastereomeric intermediates followed by post-assembly modification to remove other sources of chirality. Here, we demonstrate a simple asymmetric metal-free active template rotaxane synthesis using a primary amine, an activated ester with a chiral leaving group, and an achiral crown ether lacking rotational symmetry. Mechanically planar chiral rotaxanes are obtained directly in up to 50% enantiomeric excess. The rotaxanes were characterized by NMR spectroscopy, high-resolution mass spectrometry, chiral HPLC, single crystal X-ray diffraction, and circular dichroism. Either rotaxane enantiomer could be prepared selectively by incorporating pseudoenantiomeric cinchona alkaloids into the chiral leaving group.	May 2020
I19-Small Molecule Single Crystal Diffraction	Spontaneous assembly of rotaxanes from a primary amine, crown ether and electrophile Stephen D. P. Fielden , David A. Leigh , Charlie T. Mcternan , Borja Pérez-Saavedra , Iñigo J. Vitorica-Yrezabal Journal Of The American Chemical Society DOI: 10.1021/jacs.8b03394 Diamond Proposal Number(s): [17379] Show Abstract ▼ Abstract: We report the synthesis of crown ether-ammonium, amide and amine [2]rotaxanes via transition state stabilization of axle-forming reactions. In contrast to the two-step “clipping” and “capping” strategies generally used for rotaxane synthesis, here the components assemble into the interlocked molecule in a single, reagent-less, step under kinetic control. The crown ether accelerates the reaction of the axle-forming components through the cavity to give the threaded product in a form of metal-free active template synthesis. Rotaxane formation can proceed through the stabilization of different transition states featuring 5-coordinate (e.g., SN2) or 4-coordinate (e.g., acylation, Michael addition) carbon. Examples prepared using the approach include crown-ether-peptide rotaxanes and switchable molecular shuttles.	May 2018

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