Exploration of 1,2-phenylenediboronic esters as potential bidentate catalysts for organic synthesis

Recently, we described the first inverse electron demand Diels-Alder reaction of 1,2-diazene catalyzed by a bidentate Lewis acid. Herein we investigate 1,2-phenylenediboronic esters as potential catalysts for this transformation offering higher stability and easier handling than the currently used boranthracene derivatives. Different 1,2-phenylenediboronic esters were prepared and their ability to form bidentate coordination complexes with phthalazine was analyzed. Although a 1:1 complex was observed, X-ray analysis revealed binding only in a monodentate fashion. Graphical abstrac

Molecular Cages of Controlled Size and Shape

This thesis details the synthesis and coordination chemistry of twenty-five nitrogencontaining heterocyclic ligands, nineteen of which were previously unreported compounds. These ligands were designed for use as synthons for the formation of molecular cages, so contain multiple coordination sites capable of bridging multiple metal atoms. The majority of molecular cages in the literature are formed by rigid bridging ligands, whereas the ligands studied in this research incorporate a higher level of flexibility, thereby lessening the degree of control over the self-assembly process and increasing the number of possible structures that can be formed upon reaction of these ligands with meal salts. Three of the new ligands synthesised were two-armed bridging ligands, which were reacted with a wide variety of metal salts to investigate what self-assembly products were formed. The complexes characterised include a M₃L₃ cyclic trimer, a range of coordination polymers of varying dimensionality, a range of dimeric products and a series of M₄L₆ cage-like molecular squares. However, the majority of ligands studied were three-armed, potentially tripodal compounds, which were envisaged as potential components of M₃L₂ or M₆L₄ molecular cages. The products of self-assembly of these ligands with various metals salts were shown to include a variety of discrete tri- and tetranuclear complexes, a range of coordination polymers of varying dimensionality and interpenetration, and a complex M₆L₄ assembly that appears to be a collapsed coordination cage. Unfortunately some of the ligands synthesised were shown to decompose in the presence of various metal salts, a phenomenon already identified in the literature. Analogues of these decomposition products were synthesised deliberately to identify the potential of a known tridentate ligand as a metallosupramolecular synthon. ¹H NMR spectroscopy, mass spectrometry, elemental analysis, thermogravimetric analysis and X-ray crystallography were used to study the compounds synthesised. The crystal structures of five ligands and fifty-one complexes are discussed

Photoactive building blocks for coordination complexes: Gilding 2,2′:6′,2″-terpyridine

The alkyne unit of 4`-ethynyl-2,2`:6`,2 ``-terpyridine has been functionalized with Ph(3)PAu, (2-tolyl)(3)PAu or Au(dppe)Au units to produce compounds 1-3, respectively. These derivatives have been characterized by electrospray mass spectrometry, solution (1)H and (13)C NMR, UV-Vis and emission spectroscopies, and single crystal X-ray diffraction. In the solid state, molecules of 1 or 2 pack with separated domains of tpy and R(3)PAu units; the tpy units in 2 (but not 1) exhibit face-to-face pi-stacking. Compound 3 crystallizes as 2(3)-CHCl(3), and the folded conformation of the dppe backbone results in a short (2.9470(8) angstrom) aurophilic interaction. Folded molecule 3 captures CHCl(3), preventing intramolecular face-to-face pi-interactions between the tpy units. In CH(2)Cl(2) solution, 1-3 are emissive when excited between 230 and 300 nm, but over minutes when lambda(ex) = 230 nm, the emission bands decay as the compounds photodegrade

Do perfluoroarenearene and C–HF interactions make a difference to the structures of 4,2′:6′,4′′-terpyridine-based coordination polymers?

The consequences for the structures of coordination polymers of introducing fluoro substituents into the terminal phenyl domain of 4′-(biphenyl-4-yl)-4,2′:6′,4′′-terpyridine (1) have been investigated. Reaction between Cu(OAc)₂·H₂O and 4′-(2′,3′,4′,5′,6′-pentafluorobiphenyl-4-yl)-4,2′:6′,4′′-terpyridine (2) yields the one-dimensional coordination polymer [Cu₂(μ-OAc)₄(2)]n which contains paddle-wheel {Cu₂(OAc)₄} nodes bridged by ligands 2. The compound is isostructural with [Cu₂(μ-OAc)₄(1)]n. When Cu(OAc)₂·H₂O reacts with a 1 : 1 mixture of 1 and 2, [Cu₂(μ-OAc)₄(1)]n and [Cu₂(μ-OAc)₄(2)]n co-crystallize with 1 and 2 disordered over one ligand site; the one-dimensional coordination polymer is isostructural with each of [Cu₂(μ-OAc)₄(1)]n and [Cu₂(μ-OAc)₄(2)]n indicating that replacing H by F substituents in the peripheral arene ring has no effect on the overall solid-state structure: tpy⋯tpy π-stacking is preserved, arene⋯arene πH⋯πH interactions are replaced by perfluoroarene⋯arene πF⋯πH interactions, and H⋯H contacts are replaced by H⋯F interactions. In stark contrast to the latter observations, the reaction of Zn(OAc)₂·2H₂O with perfluoro derivative 2 yields [Zn₅(OAc)₁₀(2)₄·11H₂O]n as the dominant one-dimensional polymer; minor amounts of the anticipated polymer [Zn₂(μ-OAc)₄(2)]n are also formed. The solid-state structure of [Zn₅(OAc)₁₀(2)₄·11H₂O]n consists of quadruple-stranded polymer chains assembled from {Zn₅(2)₄} subchains interconnected by {Zn₅(OAc)₁₀} units. Within each chain, πF⋯πF and πH⋯πH stacking interactions are dominant, while the observed assembly of chains into sheets and π-stacking between arene units in adjacent sheets mimic the dominant interactions in the single-stranded chains observed in [Zn₂(μ-OAc)₄(1)]n, [Zn₂(μ-OAc)₄(2)]n, [Cu₂(μ-OAc)₄(1)]n, [Cu₂(μ-OAc)₄(2)]n and [Cu₂(μ-OAc)₄(1)]n·[Cu₂(μ-OAc)₄(2)]n

Diastereoisomeric dinuclear ruthenium complexes of 2,5-di(2-pyridyl)thiazolo[5,4-d]thiazole

The first metal complexes of 2,5-di(2-pyridyl)thiazolo[5,4-d]thiazole (5) are described. X-Ray crystal structures are reported for the free ligand 5, a dinuclear copper complex 6 and the two diastereoisomers, 7meso and 7rac, of the dinuclear bis(2,2'-bipyridine)ruthenium complex. The two diastereoisomers of 7 and the 4,4'-dimethyl-2,2'-bipyridine analogue 8 are readily separated by cation exchange chromatography. 1H NMR and visible absorption spectra and electrochemical data for the four dinuclear ruthenium complexes reveal that these have relatively small HOMO–LUMO energy gaps and exhibit relatively weak metal–metal interactions

9-Anthracenyl-substitued pyridyl enones revisited : photoisomerism in ligands and silver(I) complexes

In solution, (E) to (Z)-isomerism is facile both in 3-(9-anthracenyl)-1-(pyridin-4-yl) propenone, 2, and in its silver(I) complex [Ag(2)(2)](+). The crystal structures of (E)-2, (Z)-2 and [Ag(E)-2(2)][SbF6] are presented, and the roles of edge-to-face and face-to-face p-interactions in the lattice are discussed. Solution NMR spectroscopic data suggest that the driving force for (E) to (Z) isomerization is intramolecular p-stacking of the pyridine and anthracene domains. The reversed enone 3-(9-anthracenyl)-1-(pyridin-4-yl) propen-3-one, (E)-3, and the silver(I) complex [Ag(E)-3(2)][SbF6] have been prepared and characterized, including a single crystal X-ray determination of the latter. Surprisingly, no p-stacking between anthracene or pyridine domains is observed in the solid state, and the crystal packing is dominated by Ag center dot center dot center dot F, CHanthracene center dot center dot center dot pi-pyridine and CH center dot center dot center dot F interactions. In contrast to (E)-2 and [Ag(E)-2(2)](+), neither (E)-3 nor [Ag(E)-3(2)](+) undergoes photoisomerization in solution

Zinc(II) coordination polymers, metallohexacycles and metallocapsules – do we understand self-assembly in metallosupramolecular chemistry : algorithms or serendipity?

Using a strategy of layering solvents and solutions of ligands and metal salts under ambient conditions, we observe the assembly of a discrete molecular metallohexacycle from ZnCl2 and 4`-(4-ethynylphenyl)-4,2`:6`,4 ``-terpyridine, polycatenated, triply interlocked metallocapsules from ZnI2 and 4`-(4-pyridyl)-4,2`:6`,4 ``-terpyridine, and 1-dimensional coordination polymers from either ZnCl2 or ZnI2 with 4`-4-( 3-chloropyridyl)-4,2`:6`,4 ``-terpyridine. On the basis of these studies and a comparison with related structures in the literature, we urge crystal engineers to be wary of drawing conclusions about self-assembly algorithms in solution using data from single crystal determinations

Disulfide struts : assembly motifs supporting a cuprocapsule

Condensation of 2-aminoethanethiol with 1,3-bis(3-formyl-2-hydroxyphenyl)-1,4,7,10,13-pentaoxatridecane in the presence of Cu(OAc)(2) and base is accompanied by oxidative coupling of pendant thiols with the formation of a disulfide-containing macrocycle H(2)1. This assembles the novel capsule [Cu-2(1)(2)] which hosts two CH2Cl2 guest molecules

Multinuclear zinc(II) complexes with Zn-6(mu-O)(6)(mu(3)-O)(2)- and Zn-5(mu-O)(3)(mu(3)-O)(3)-cluster cores

2-Ethoxy-6-(((2-hydroxyphenyl)imino)methyl)phenol, H21, reacts with zinc(II) chloride in basic conditions to give [Zn6(1)4Cl2(OH)2(OH2)2]. The electrospray mass spectrum of a MeOH solution of the bulk sample provides evidence for {Znn(1)n} species with n = 2–5, while the 1H NMR spectrum of a CDCl3 solution of the bulk sample indicates the presence of at least four species. Single crystals of 2{[Zn6(1)4Cl2(OH)2(OH2)(MeOH)]}·4MeOH·8H2O and 2{[Zn5(1)5(MeOH)(OH2)]}·6MeOH·H2O were obtained from the same solution of [Zn6(1)4Cl2(OH)2(OH2)2] in CH2Cl2/MeOH. Structural determinations confirm that these compounds contain {Zn6(μ-O)6(μ3-O)2}- and {Zn5(μ-O)3(μ3-O)3}-cluster cores, respectively, revealing that the O,O′,N,O″-donor set in [1]2− is suited to the assembly of relatively high nuclearity zinc(II)-containing clusters