Carbon Dioxide Fixation and Sulfate Sequestration by a Supramolecular Trigonal Bipyramid

The subcomponent self‐assembly of a bent dialdehyde ligand and different cationic and anionic templates led to the formation of two new metallosupramolecular architectures: a Fe^II₄L₆ molecular rectangle was isolated following reaction of the ligand with iron(II) tetrafluoroborate, and a M₅L₆ trigonal bipyramidal structure was constructed from either zinc(II) tetrafluoroborate or cadmium(II) trifluoromethanesulfonate. The spatially constrained arrangement of the three equatorial metal ions in the M₅L₆ structures was found to induce small‐molecule transformations. Atmospheric carbon dioxide was fixed as carbonate and bound to the equatorial metal centers in both the Zn₅L₆ and Cd₅L₆ assemblies, and sulfur dioxide was hydrated and bound as the sulfite dianion in the Zn₅L₆ structure. Subsequent in situ oxidation of the sulfite dianion resulted in a sulfate dianion bound within the supramolecular pocket.     

Luminescent Pt(II)(bipyridyl)(diacetylide) chromophores with pendant binding sites as energy donors for sensitised near-infrared emission from lanthanides: structures and photophysics of Pt(II)/Ln(III) assemblies

The complexes [Pt(bipy){CC-(4-pyridyl)}(2)] (1) and [Pt(tBu(2)bipy){CC-(4-pyridyl)}(2)] (2) and [Pt(tBu(2)-bipy)(CC-phen)(2)] (3) all contain a Pt(bipy)(diacetylide) core with pendant 4-pyridyl (1 and 2) or phenanthroline (3) units which can be coordinated to {Ln(diketonate)(3)} fragments (Ln = a lanthanide) to make covalently-linked Pt(II)/Ln(III) polynuclear assemblies in which the Pt(II) chromophore, absorbing in the visible region, can be used to sensitise near-infrared luminescence from the Ln(III) centres. For 1 and 2 one-dimensional coordination polymers [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) are formed, whereas 3 forms trinuclear adducts [3{Ln(hfac)(3)}(2)] (tta=anion of thenoyl-trifluoroacetone; hfac=anion of hexafluoroacetylacetone). Complexes 1-3 show typical Pt(II)-based (3)MLCT luminescence in solution at approximately 510 nm, but in the coordination polymers [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) the presence of stacked pairs of Pt(II) units with short PtPt distances means that the chromophores have (3)MMLCT character and emit at lower energy ( approximately 630 nm). Photophysical studies in solution and in the solid state show that the (3)MMLCT luminescence in [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) in the solid state, and the (3)MLCT emission of [3{Ln(hfac)(3)}(2)] in solution and the solid state, is quenched by Pt-->Ln energy transfer when the lanthanide has low-energy f-f excited states which can act as energy acceptors (Ln=Yb, Nd, Er, Pr). This results in sensitised near-infrared luminescence from the Ln(III) units. The extent of quenching of the Pt(II)-based emission, and the Pt-->Ln energy-transfer rates, can vary over a wide range according to how effective each Ln(III) ion is at acting as an energy acceptor, with Yb(III) usually providing the least quenching (slowest Pt-->Ln energy transfer) and either Nd(III) or Er(III) providing the most (fastest Pt-->Ln energy transfer) according to which one has the best overlap of its f-f absorption manifold with the Pt(II)-based luminescence.     

M3L2 metallo-cryptophanes: [2]catenane and simple cages

Crystalline M(3)L(2) complexes with either single cage or triply interlocking [2]catenane chiral structures are formed the self-assembly of host-like ligands with transition metals.     

Reversible reduction drives anion ejection and C60 binding within an FeII4L6 cage

Fe^II₄L₆ tetrahedral cage 1 was prepared from a redox-active dicationic naphthalenediimide (NDI) ligand. The +20 charge of the cage makes it a good host for anionic guests, with no binding observed for neutral aromatic molecules. Following reduction by Cp₂Co, the cage released anionic guests; subsequent oxidation by AgNTf₂ led to re-uptake of anions. In its reduced form, however, 1 was observed to bind neutral C₆₀. The fullerene guest was subsequently ejected following cage re-oxidation. The guest release process was found to be facilitated by anion-mediated transport from organic to aqueous solution. Cage 1 thus employs electron transfer as a stimulus to control the uptake and release of both neutral and charged guests, through distinct pathways.

Fe^II₄L₆ cage 1 binds anionic guests but not neutral guests. In its reduced form, the cage can bind neutral C₆₀. Reduction and oxidation of the cage could thus be used as a stimulus to control the uptake and release of both neutral and charged guests.     

Selective Endo and Exo Binding of Mono‐ and Ditopic Ligands to a Rhomboidal Diporphyrin Prism

Copper(I) can preferentially form heteroleptic complexes containing two phosphine and two nitrogen donors due to steric factors. This preference was employed to direct the self‐assembly of a porphyrin‐faced rhomboidal prism having two parallel tetrakis(4‐iminopyridyl)porphyrinatozinc(II) faces linked by eight 1,4‐bis(diphenylphosphino)benzene pillars. The coordination preferences of the Cu^I ions and geometries of the ligands come together to generate a slipped‐cofacial orientation of the porphyrinatozinc(II) faces. This orientation enables selective encapsulation of 3,3′‐bipyridine (bipy), which bridges the Zn^II ions of the parallel porphyrins, whereas 4,4′‐bipy exhibits weaker external coordination to the porphyrin faces. Reaction with 2,2′‐bipy, by contrast, results in the displacement of the tetratopic porphyrin ligand and formation of [{(2,2′‐bipy)Cu^I}₂(diphosphine)₂]. The differing strengths of interactions of bipyridine isomers with the system allows for a hierarchy to be deciphered, whereby 4,4′‐bipy may be displaced by 3,3′‐bipy, which in turn is displaced by 2,2′‐bipy.     

The dimeric "hand-shake" motif in complexes and metallo-supramolecular assemblies of cyclotriveratrylene-based ligands

A series of clathrate and metal complexes with cyclotriveratrylene-like molecular host ligands show a similar dimeric homomeric inclusion motif in which a ligand arm of one host is the intra-cavity guest of another and vice versa. This "hand-shake" motif is found in the trinuclear transition metal complex [Cu(3)Cl(6)(1)]CH(3)CN1.5 H(2)O in which 1 is tris(4-[2,2',6',2'-terpyridyl]benzyl)cyclotriguaiacylene; in the self-included M(4)L(4) tetrahedral metallo-supramolecular assembly [Ag(4)(2)(4)] (BF(4))(4) in which 2 is tris-(2-quinolylmethyl)cyclotriguaiacylene; in the 1D coordination chains [Ag(4)]ReO(4) CH(3)CN and [Ag(5)]SbF(6)3 DMFH(2)O in which 4 is tris(1H-imidazol-1-yl)cyclotriguaiacylene and 5 is tris{4-(2-pyridyl)benzyl}cyclotriguaiacylene; and in the acetone clathrate of tris{4-(2-pyridyl)benzyl-amino}cyclotriguaiacylene. Clathrates of ligands 2 and 5 do not show the same dimeric motif, although 2 has an extended homomeric inclusion motif that gives a hexagonal network.     

Ruthenium‐Catalyzed Reductive Arylation of N‐(2‐Pyridinyl)amides with Isopropanol and Arylboronate Esters

A new three‐component reductive arylation of amides with stable reactants (iPrOH and arylboronate esters), making use of a 2‐pyridinyl (Py) directing group, is described. The N‐Py‐amide substrates are readily prepared from carboxylic acids and PyNH₂, and the resulting N‐Py‐1‐arylalkanamine reaction products are easily transformed into the corresponding chlorides by substitution of the HN‐Py group with HCl. The 1‐aryl‐1‐chloroalkane products allow substitution and cross‐coupling reactions. Therefore, a general protocol for the transformation of carboxylic acids into a variety of functionalities is obtained. The Py‐NH₂ by‐product can be recycled.     

AuICl-bound N-heterocyclic carbene ligands form MII4(LAuCl)6 integrally gilded cages

The incorporation of an N-heterocyclic carbene (NHC) moiety into a self-assembled MII4L₆ cage framework required the NHC first to be metallated with gold(i). Bimetallic cages could then be constructed using zinc(ii) and cadmium(ii) templates, showing weak luminescence. The cages were destroyed by the addition of further gold(i) in the form of Au^I(2,4,6-trimethoxybenzonitrile)₂SbF₆, which caused the reversibly-formed cages to disassemble and controllably release the Au^I-NHC subcomponent into solution. This release in turn induced the growth of gold nanoparticles. The rate of dianiline release could be tuned by capsule design or through the addition of chemical stimuli, with different release profiles giving rise to different nanoparticle morphologies.