Paul J. Lusby

Luminescent, enantiopure, phenylatopyridine iridium-based coordination capsules

The first molecular capsule based on an [Ir(ppy)(2)](+) unit (ppy = 2-phenylatopyridine) has been prepared. Following the development of a method to resolve rac-[(Ir(ppy)(2)Cl)(2)] into its enantiopure forms, homochiral Ir(6)L(4) octahedra where obtained with the tritopic 1,3,5-tricyanobenzene. Solution studies and X-ray diffraction show that these capsules encapsulate four of the six associated counteranions and that these can be exchanged for other anionic guests. Initial photophysical studies have shown that an ensemble of weakly coordinating ligands can lead to luminescence not present in comparable mononuclear systems.

An Ion-Pair Template for Rotaxane Formation and its Exploitation in an Orthogonal Interaction Anion-Switchable Molecular Shuttle

Despite significant advances in anion-template methods for the construction of mechanically interlocked molecules, the use of anions to induce changes in the relative positions of the components of catenanes and rotaxanes has proved particularly challenging, especially in comparison to the widespread success achieved with other stimuli. The few examples of anion-switchable molecular shuttles developed to date employ competition between the same types of weak interaction in both states of the molecule to achieve switching (solvation effects or the anion outcompeting hydrogenbonding acceptor groups of the macrocycle for donor groups on the thread [3e, ). Other features of anions, such as the propensity of halides to form strong coordination bonds to various transition metals, have yet to be exploited. Herein we report the serendipitous discovery of a new efficient template for rotaxane formation and its use in the assembly of a chloride-switchable molecular shuttle which exhibits excellent positional integrity (> 98%) of the ring in both states that arises from orthogonal binding modes: direct intercomponent metal–ligand coordination in one state and a combination of tight ion pairing, aromatic stacking interactions, and CH···O and CH···Cl hydrogen bonding in the other. The development of the new template for rotaxane formation was prompted by the chance observation that displacement of the acetonitrile ligand of [(L1)Pd(CH3CN)] by the chloride ion of benzyl pyridinium chloride (1-Cl) was accompanied by encapsulation of the organic cation by the anionic PdCl-coordinated macrocycle [(L1)PdCl] (Figure 1a). The threaded nature of the complex [(L1)PdCl·1] in CDCl3 was clearly apparent from H NMR spectroscopy (a distinct upfield shift in the pyridinium resonances with respect

Stimuli-Responsive Reversible Assembly of 2D and 3D Metallosupramolecular Architectures

The discovery of interconvertible platinum coordination modes, which reveals and masks cis coordinating groups upon addition of acid and base, respectively, has been exploited to facilitate stimuli-responsive assembly and disassembly of both two- and three-dimensional metallosupramolecular architectures. Treatment of a binclear platinum complex with acid along with ditopic and tritopic donor ligands generated a molecular square and a trigonal prism, respectively, in good to high yield. These complexes were unambiguously identified using electrospray mass spectrometry, (1)H NMR spectroscopy, and X-ray crystallography. Both assemblies can be disassembled into their constituent parts simply by treatment with base, and the prism can be cycled between the assembled and disassembled states by the alternate addition of acid and base.

Gold(I)-template catenane and rotaxane synthesis

The last of the simple metal coordination geometries (linear) joins the family of metal–ligand arrangements that have been used to template the formation of mechanical bonds. Both catenanes and rotaxanes are assembled about a gold(I) template.

Sequence isomerism in [3]rotaxanes.

We describe a strategy for assembling different macrocycles onto a nonsymmetrical rotaxane thread in a precise sequence. If the macrocycles are small and rigid enough so that they cannot pass each other then the sequence is maintained mechanically, affording stereoisomerism in a manner reminiscent of atropisomerism. The method is exemplified through the synthesis of a pair of [3]rotaxane diastereomers that are constitutionally identical other than for the sequence of the different macrocycles on the thread. The synthesis features the iterative binding of different palladium(II) pyridine-2,6-dicarboxamide complexes to a pyridine ligand on the thread followed by their macrocyclization by ring-closing olefin metathesis. Removal of the palladium(II) from the first rotaxane formed frees the pyridine site to coordinate to a second, different, palladium(II) pyridine-2,6-dicarboxamide unit which, following macrocyclization, provides a multiring rotaxane of predetermined macrocycle sequence.

Active Template Synthesis of Rotaxanes and Molecular Shuttles with Switchable Dynamics by Four-Component PdII-Promoted Michael Additions

Rotaxanes and molecular shuttles are prepared in up to 99?% yield by successive PdII-promoted 1,4-conjugate additions in a one-pot four-component assembly process. This process represents the first active template reaction in which the template motif is retained in the interlocked product.

Shapes of supramolecular cages by ion mobility mass spectrometry

Mass spectrometry and drift tube ion mobility mass spectrometry have been used to analyse several isobaric, multicomponent cages yielding information on three dimensional structure, interactions and dynamics of assembly in the gas phase.

Sequential, Kinetically Controlled Synthesis of Multicomponent Stereoisomeric Assemblies†

The reversibility of noncovalent and metal–ligand interactions has widely been exploited to synthesize a plethora of supramolecular and coordination-based assemblies under thermodynamic control. Occasionally, entrapment in local energy minima leads to the formation of metastable products, which are often converted into lower-energy products upon prolonged reaction times. In contrast, self-assembled products in nature almost always arise according to the most expedient reaction pathway, that is, the kinetically selected. Herein we demonstrate a kinetically controlled approach to self-assembly, in which the sequence of addition of molecular structural units leads to the stereoselective formation of metallosupramolecular isomers. The use of platinum(II) (and other third-row transition metals) is particularly well-suited to a kinetic approach to self-assembly, not just because Pt–ligand bonds can be kinetically inert, but also because the metal ion can be conveniently tuned to produce a vast range of different ligand-exchange labilities. For instance, assemblies that utilize bis(phosphine) ligands as corner protecting groups often readily assemble at room temperature, while those that exploit neutral N-donor bidentate ligands, such as ethylene diamine, typically require several hours at elevated temperature to reach equilibrium. Furthermore, the mechanism of labilization, that is, the trans effect, is such that it is possible for a single metal center to possess cis exchangeable sites with dramatically different kinetic properties. We have recently prepared a metallosupramolecular trigonal prism that possesses an unsymmetrical cyclometalated C _ N corner protecting group, which was assembled in two steps by treating [LPt(dmso)] (where H2L 1 = 2,6-diphenylpyridine) sequentially with 4,4’-bipy and tpt.3CSA (Scheme 1, steps a and b). The isolation of a single isomeric product from a possible fourteen products, as indicated by the H NMR spectrum of the hexa-PF6 salt (see the Supporting Information, Figure S1a), led us to ask, was this selectivity a result of each Pt center possessing one labile and one inert exchangeable site, or was the selectivity thermodynamic in origin? To answer this question, the sequence in which 4,4’-bipy and tpt were added to [LPt(dmso)] was reversed. [LPt(dmso)] was first treated with a third of an equivalent of tpt at room temperature in CH2Cl2 to give [(L Pt)3(tpt)] (Scheme 1, step c), which was then treated with 4,4’-bipy·2CSA, and after metathesis with NH4PF6, the hexa-PF6 salt was isolated in 99% yield (Scheme 1, step d). The H NMR spectrum of this product (see the Supporting Information, Figure S1b) also indicated the formation of a single species, yet there were clear differences between the spectra of the two isomers, in particular, for resonances HA-E. The product from route 1 was assigned as cis-[(HLPt)6(4,4’-bipy)3(tpt)2](PF6)6, in which the tpt ligand is coordinated cis to the nitrogen of the 2,6diphenylpyridine ligand, and the product from route 2 was assigned as trans-[(HLPt)6(4,4’-bipy)3(tpt)2](PF6)6, in which the tpt ligand is coordinated trans to the nitrogen of the 2,6diphenylpyridine ligand. This absolute assignment was made on the basis that a) the resonance of the ortho proton of tpt (HC) is more deshielded in the trans-to-nitrogen coordination site in comparison to the ortho proton 4,4’-bipy (HB), and b) the large and small relative separations between the resonances of HA and HB, and between the resonances of HC and HD. Scheme 1. Sequence-specific control over the formation of metallosupramolecular stereochemical isomers. a) 4,4’-bipy, CH2Cl2, RT, 18 h, 77%; b) (i) tpt·3CSA, CH2Cl2, RT, 1 h; (ii) NH4PF6, 97%; c) tpt, CH2Cl2, 18 h, 85%; d) (i) 4,4’-bipy·2CSA, CH2Cl2, RT, 3 h; (ii) NH4PF6, 99 %. bipy= bipyridine, CSA = camphorsulfonic acid, dmso = dimethylsulfoxide, tpt = tris(4-pyridyl)triazine.

Maximizing Coordination Capsule–Guest Polar Interactions in Apolar Solvents Reveals Significant Binding

Guest encapsulation underpins the functional properties of self-assembled capsules yet identifying systems capable of strongly binding small organic molecules in solution remains a challenge. Most coordination capsules rely on the hydrophobic effect to ensure effective solution-phase association. In contrast, we show that using non-interacting anions in apolar solvents can maximize favorable interactions between a cationic Pd2 L4 host and charge-neutral guests resulting in a dramatic increase in binding strength. With quinone-type guests, association constants in excess of 108  m-1 were observed, comparable to the highest previously recorded constant for a metallosupramolecular capsule. Modulation of optoelectronic properties of the guests was also observed, with encapsulation either changing or switching-on luminescence not present in the bulk phase.

Combining Complementary Ligands into one Framework for the Construction of a Ferromagnetically Coupled {[}Mn-12(III)] Wheel

Phenolic oxime and diethanolamine moieties have been combined into one organic framework, resulting in the formation of a novel ligand type that can be employed to construct a rare and unusual dodecametallic Mn wheel, within which nearest neighbours are coupled ferromagnetically.