Guest-Shuttling in a Nanosized Metallobox.

An iridium-conjoined long and narrow metallorectangle was obtained by combining a quinoxalinophenanthrophenazine-connected Janus-di-imidazolylidene ligand and pyrazine. The size and shape of this assembly together with the fused polyaromatic nature of its panels provides it with properties that are uncommon for other metallosupramolecular assemblies. For example, this nanosized 'slit-like' metallobox is able show very large binding affinities with planar organic molecules in such a way, that the cavity is asymmetrically occupied by the guest molecule. This unsymmetrical conformation leads to the existence of a large amplitude motion of these guests, which slide between the two sides of the cavity of the host, thus constituting rare examples of molecular shuttles.

Gram-Scale Synthesis of the 1,1,n,n-Tetramethyl[n](2,11)teropyrenophanes.

A gram-scale synthesis of a series of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n=7-9) has been accomplished as well as the first synthesis of the next higher homologue 1,1,10,10-tetramethyl[10](2,11)teropyrenophane. The scale-up of the original small-scale synthesis required the development of several heavily modified synthetic methods, including a chlorination/Friedel-Crafts alkylation protocol and an iodination/Wurtz coupling protocol, which were performed on 25-30 g and 30-60 g scales, respectively. Two separate sets of conditions for the key teropyrene-forming cyclodehydrogenation reaction at the end of the synthetic pathway were developed, an acid-promoted one for the two less strained congeners and an acid-free method for the two more strained homologues.

"Shadow" Synthesis, Structure, and Electronic Properties of [2.2](1,6)(1,8)Pyrenophane-1-monoene.

An unexpected side product of a McMurry reaction was found to be a new [2.2]pyrenophane consisting of two pyrene units with different substitution patterns as well as different types and degrees of distortion from planarity. The new pyrenophane exhibits both monomer and intramolecular excimer fluorescence. Natural bond orbital (NBO) analysis revealed that there is an intramolecular charge-transfer interaction from the more distorted pyrene system to the less distorted one. The origin of the new pyrenophane was traced back to an impurity that was present a full five steps prior to the McMurry reaction from which it was isolated. The pathway to the pyrenophane shadowed that of the main synthetic route.

The Milstein Bipyridyl PNN Pincer Complex of Ruthenium Becomes a Noyori-Type Catalyst under Reducing Conditions.

Hydrogenation of the dearomatized PNN ligand of the Milstein bipyridyl complex RuH(CO)[PNN] (2) gives a square-pyramidal Ru(II) product RuH(CO)[pPNN] (5). The central ring of the pPNN ligand is a piperidine. A minor byproduct of the hydrogenation reaction is complex 6 which has a dimeric structure made of two Ru(II) fragments each possessing a partly hydrogenated PNN ligand. The structures of 5 and 6 have been elucidated by NMR spectroscopy and X-ray crystallography. The PNN ligand of 2 is also hydrogenated under the conditions of the catalytic dehydrogenative coupling of ethanol to ethyl acetate. No direct evidence of the aromatized dihydride RuH2(CO)[PNN] (4) was found in this study. However, treating RuHCl(CO)[PNN] with Li[HBEt3] or reacting 2 with H2 at low temperature resulted in a structurally characterized hydride-bridged dimer (7) bearing intact aromatized bipyridyl ligands. M06-L/def2-QZVP DFT calculations provided insights into the thermodynamics of the stoichiometric reactions of this work and into the nature of the intermediates of the catalytic ester hydrogenation facilitated by RuH2(CO)[pPN(H)N] (8) formed from 5 under H2.

Synthesis and Characterization of Liquid-Crystalline Tetraoxapentacene Derivatives Exhibiting Aggregation-Induced Emission.

A series of new tetrakis(dialkoxyphenyl) dicyanotetraoxapentacene derivatives (1 a-c) were prepared by reaction of the appropriate terphenyl diols with tetrafluoroterephthalonitrile in good yields. Compounds 1 b and 1 c, which bear hexyloxy and decyloxy side chains, exhibited columnar hexagonal mesophases, as shown by polarized optical microscopy, variable-temperature powder X-ray diffraction, and differential scanning calorimetry. Single-crystal X-ray diffraction of methoxy-substituted 1 a revealed that the dicyanotetraoxapentacene core is highly planar, consistent with the notion that these molecules are able to stack in columnar mesophases. A detailed photophysical characterization showed that these compounds exhibit aggregation-induced emission in solution, emission in nonpolar solvents, weak emission in polar solvents, and strong emission in the solid state both as powder and in thin films. These observations are consistent with a weakly emissive charge-transfer state in polar solvents and a more highly emissive locally excited state in nonpolar solvents.

Synthesis of Emissive Heteroacene Derivatives via Nucleophilic Aromatic Substitution.

A synthetic approach for preparing a variety of heterocyclic tetrahydropentacene derivatives via nucleophilic aromatic substitution reactions of bidentate nucleophiles and tetrafluoroterephthalonitrile was developed. X-ray crystallography of several products revealed that the compounds containing oxygen and nitrogen heteroatoms are highly planar and engage in π-stacking, while the compounds containing sulfur are bent and do not stack as effectively. The compounds were also highly emissive, and the heteroatom had a significant impact on the emission and electrochemical properties.

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone.

The first structures exhibiting bidentate (N, O) chelation of a morpholine group to a p-block element (aluminum) have been prepared and characterized by X-ray diffraction methods: Al[L]+ [WCA]-, where [L] = 4-(2-aminoethyl)morpholinylamino- N, N-bis(2-methylene-4,6- tert-butylphenolate) and [WCA]- is a weakly coordinating anion. These compounds are easily synthesized by reacting Al[L]Cl with an equimolar amount of anhydrous Lewis acid and were characterized by elemental analyses, ESI-MS, MALDI-TOF MS, 1H, 13C{1H}, and multinuclear NMR spectroscopy. DFT calculations showed that Al[L]+ cations containing bidentate NO coordination of the morpholine group are at least 21.1 kJ/mol more stable when compared to hypothetical monodentate (N bound) structures. When combined with protic co-initiators (EtOH, glycerol carbonate), the cationic complexes, where [WCA]- = [GaCl4]- or [InCl4]-, are living catalyst systems for the polymerization of ε-caprolactone, producing polycaprolactone with narrow dispersity ( D̵ = 1.00-1.05). Employing glycidol as a co-initiator furnished polymers with narrow dispersity ( D̵ = 1.01-1.07) but experimental molecular weights diverged considerably from the calculated values. Similar reactivity toward ROP was observed for all complexes containing a stable [WCA]- but where [WCA]- = [AlCl4]-, upon combination with alcohols, alcoholysis was observed. Kinetic studies (Eyring analyses) allowed the determination of activation parameters, which were consistent with a coordination-insertion mechanism for the catalysts containing [WCA]- = [GaCl4]- or [InCl4]-. End group analyses using MALDI-TOF mass spectrometry and 1H NMR spectroscopy showed hydroxyl and ester end groups within the polymer, corroborating the proposed mechanism. Stoichiometric reactions of EtOH, glycidol or tert-butyl alcohol with the complex, where [WCA]- = [GaCl4]-, showed protonation of the ligand at the N-morpholine site, which leads to dissociation of this pendent group.

Structures, Phase Behavior, and Fluorescent Properties of 3-Phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine and Its ZnCl2 Complex.

The synthesis of the asymmetric ligand 3-phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine (L1) and its single-crystal X-ray structure are reported. L1 displays crystallographic symmetry (orthorhombic, Pccn) higher than its molecular symmetry (point group C1) and also displays supercooling, with a difference in the melting and solidification points of over 100 °C. Upon complexation with ZnCl2, L1 engages in both primary cation and secondary anion coordination via hydrogen bonding, and the complex exhibits a room-to-low-temperature single crystal-to-crystal phase transition. The ZnCl2 complex becomes a birefringent fluid mixed with crystalline domains at high temperatures, as detected by polarized optical microscopy. Examination of the photoluminescence properties showed that the emission intensity increased and a pronounced bathochromic shift was observed in the emission maximum upon going from solution to the solid state, for both the ligand and complex, consistent with aggregation-induced emission behavior.

Contractive Annulation: A Strategy for the Synthesis of Small, Strained Cyclophanes and Its Application in the Synthesis of [2](6,1)Naphthaleno[1]paracyclophane.

A new synthetic strategy (contractive annulation) for the synthesis of highly strained cyclophanes has been conceived and its viability has been demonstrated through a nine-step synthesis of [2](6,1)naphthaleno[1]paracyclophane from [2.2]paracyclophane.

Gram-Scale Synthesis and Highly Regioselective Bromination of 1,1,9,9-Tetramethyl[9](2,11)teropyrenophane.

An improved synthetic pathway to the nanobelt-like 1,1,9,9-tetramethyl[9](2,11)teropyrenophane has been developed, and enables the synthesis of gram quantities of material. Key innovations are the development of a sequential chlorination/Friedel-Crafts alkylation reaction, a sequential iodination/Wurtz coupling reaction, and a room-temperature teropyrene-forming reaction. The teropyrenophane was found to form a very stable radical cation and undergo a completely regioselective fourfold bromination reaction.

Oligonuclear Fe complexes (Fe, Fe4, Fe6, Fe9) derived from tritopic pyridine bis-hydrazone ligands-structural, magnetic, and Mössbauer studies.

Tri-topic pyridine bis-hydrazone ligands produce polynuclear complexes with Fe(II) and Fe(III) salts with varying nuclearity and metal ion oxidation states. Mononuclear, tetranuclear, hexanuclear, and nonanuclear examples are discussed using structural, magnetic and Mössbauer data. In one case, although X-ray data suggest a [3 × 3] Fe9 grid (space group P42/n), careful examination of the structure, in conjunction with magnetic and Mössbauer data, indicates an unusual situation where the corner and center sites are present at unit occupancy, whereas side site occupancy is ∼0.6.

Self-assembled Ln(III)4 (Ln = Eu, Gd, Dy, Ho, Yb) [2 × 2] square grids: a new class of lanthanide cluster.

Self-assembly of the Ln(III) ions (Ln = Eu, Gd, Dy, Ho, Yb) into square [2 × 2] grid-like arrays has been readily effected using simple, symmetric ditopic ligands based on a carbohydrazone core. The metal ions are connected via single atom bridges (e.g., µ2-O(hydrazone), µ2-OH, µ2-OMe, µ2-1,1-N3(-), µ4-O), depending on reaction conditions. The Gd(III)4 examples exhibit intramolecular antiferromagnetic exchange (-J < 0.11 cm(-1)), and in one Dy(III)4 example, with a combination of µ2-1,1-N3(-), and µ4-O bridges linking adjacent metal ions, SMM behavior is observed. One thermally driven relaxation process is observed in the temperature range 10-25 K (τ0 = 6.5(1) × 10(-7) s, U(eff) = 110(1) K) in the presence of an 1800 Oe external field, employed to suppress a second quantum based relaxation process. The extended group of Ln(III) ions which submit to this controlled self-assembly, typical of the transition metal ions, indicates the general applicability of this approach to the lanthanides. This occurs despite the anticipated limitations based on larger ionic radii and coordination numbers, and is an encouraging sign for extension to larger grids with appropriately chosen polytopic ligands.

Synthesis, crystal structure, and Hirshfeld surface analysis of 3-ferrocenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine.

A key step towards utilizing polynuclear metal-based systems in magnetic device applications involves the careful design of ligands. This strategic planning aims to produce metal assemblies that exhibit some kind of 'switch' mechanism. Towards this end, a ligand that incorporates a redox-active functional group (ferrocene) is reported. This communication presents the multi-step synthesis, characterization (1H and 13C NMR), and structural analysis (single-crystal X-ray diffraction and Hirshfeld surface analysis) of 3-ferrocenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine, [Fe(C5H5)(C13H11N4)]. Supra-molecular features, including π-π stacking and hydrogen bonding are qu-anti-fied, while a database search reveals the unique combination of mol-ecular moieties, which offer future opportunities for studies to involve simultaneous Lewis acid and base coordin-ation.

Controlled synthesis of polycarbonate diols and their polylactide block copolymers using amino-bis(phenolate) chromium hydroxide complexes.

A diamine-bis(phenolate) chromium(III) complex, CrOH[L] ([L] = dimethylaminoethylamino-N,N-bis(2-methylene-4,6-tert-butylphenolate)), 2, in the presence of tetrabutylammonium hydroxide effectively copolymerizes CO2 and cyclohexene oxide (CHO) into a polycarbonate diol. The resultant low molar mass (6.3 kg mol-1) diol is used to initiate ring-opening polymerization of rac-lactide with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) giving ABA-type block copolymers with good molar mass control through varying rac-LA-to-diol loadings and with narrow dispersities. As the degree of rac-LA incorporation increases, the glass transition temperatures (Tg) are found to decrease, whereas decomposition temperatures (Td) increase. (Diphenylphosphonimido)triphenylphosphorane (Ph2P(O)NPPh3) was used as a neutral nucleophilic cocatalyst with 2, giving phosphorus-containing polycarbonates with an Mn value of 28.5 kg mol-1, a dispersity of 1.13, a Tg value of 110 °C and a Td value of over 300 °C. A related Cr(III) complex (4) having a methoxyethyl pendent group rather than a dimethylaminoethyl group was structurally characterized as a hydroxide-bridged dimer.

Synthesis, crystal structure, and resolution of [10](1,6)pyrenophane: an inherently chiral [N]cyclophane.

A synthetic approach to a set of three inherently chiral [n]cyclophanes, [n](1,6)pyrenophanes (29a-c, n = 8-10) was investigated. Progress toward 29a was thwarted by the failure of the key dithiacyclophane-forming reaction. For the next higher homologue, the synthesis was completed, but the desired [9](1,6)pyrenophane (29b) could only be partially separated from an isomeric pyrenophane, [9](1,8)pyrenophane (28b), and an unidentified byproduct. Work aimed at the synthesis of the next higher homologue resulted in the isolation of a 7:4 mixture of [10](1,8)pyrenophane (28c) and [10](1,6)pyrenophane (29c), which could not be separated by column chromatography or crystallization. However, single-crystal X-ray structures of 28c and 29c were obtained after manual separation of two crystals with different morphologies from the same batch of crystals obtained from the 7:4 mixture of 28c and 29c. The pyrene system of 29c was found to have a gentle end-to-end bend as well as a significant longitudinal twist. Short intermolecular C(sp(3))-H···π contacts (2.64 to 2.76 Å) between H-atoms on the bridge and the centroids of three of the four six-membered rings of the pyrene system of a neighboring pyrenophane of like chirality give rise to the formation of single enantiomer columns. From a DNMR study of the mixture of 28c and 29c, the bridge in [10](1,8)pyrenophane (28c) was found to undergo a conformational flip from one side of the pyrene system to the other with ΔG(‡) = 14.9 ± 0.2 kcal/mol. A two-stage preparative HPLC protocol was subsequently developed for the separation of 28c and 29c (Chiralpak AD-H column) and then the enantiomers of 29c (Chiralcel OJ-H column). This enabled the measurement of their optical rotations and CD spectra.

Copolymerization of cyclohexene oxide and CO2 with a chromium diamine-bis(phenolate) catalyst.

A diamine-bis(phenolate) chromium(III) complex, {CrCl[O(2)NN'](BuBu)}(2) catalyzes the copolymerization of cyclohexene oxide with carbon dioxide. The synthesis of this metal complex is straightforward, and it can be obtained in high yields. This catalyst incorporates a tripodal amine-bis(phenolate) ligand, which differs from the salen or salan ligands typically used with Cr and Co complexes that have been employed as catalysts for the synthesis of such polycarbonates. The catalyst reported herein yields low molecular weight polymers with narrow polydispersities. Structural and spectroscopic details of this complex along with its copolymerization activity for cyclohexene oxide and carbon dioxide are presented.

Lanthanide complexes of tritopic bis(hydrazone) ligands: single-molecule magnet behavior in a linear Dy(III)3 complex.

Tritopic pyridinebis(hydrazone)-based ligands typically produce square M(9) [3 × 3] grid complexes with first-row transition-metal ions (e.g., M = Mn, Fe, Co, Cu, Zn), but with larger lanthanide ions, such coordination motifs are not produced, and instead linear trinuclear complexes appear to be a preferred option. The reaction of 2pomp [derived from pyridine-2,6-bis(hydrazone) and 2-acetylpyridine] with La(III), Gd(III), and Dy(III) salts produces helical linear trinuclear [Ln(3)(2pomp)(2)]-based complexes, where each metal ion occupies one of the three tridentate ligand pockets. Two ligands encompass the three metal ions, and internal connections between metal ions occur through µ-O(hydrazone) bridges. Coligands include benzoate, nitrate, and N,N-dimethylformamide. The linear Dy(III)(3) complex exhibits single-molecule magnet behavior, demonstrated through alternating-current susceptibility measurements. Slow thermal magnetic relaxation was detected in an external field of 1800 Oe, where quantum-tunneling effects were suppressed (U(eff) = 14 K).

µ-O bridged Mn10 assemblies with open O6 sites for binding extra guests: structural, magnetic, and surface studies.

High nuclearity [Mn(10)M(2)] clusters have been achieved through a self-assembly approach where multiple coordinating functional groups are incorporated into one ligand. When the hydrazone group appended with an oxime function as a reactive intermediate is used, the attachment of a vanillin subunit creates a ligand (L4) with three coordinating groups, which in their own right lead to cluster assemblies. The trifunctional ligand L4 produces a series of self-assembled, mixed oxidation state (Mn(II)/Mn(III)) Mn(10)M(2) based clusters with an overall linear structure comprising two connected pentanuclear Mn(5) halves, which bind alkali metal cations (M = Li, Na, K, Rb, Cs) and H(3)O(+) in the vanillin (O(6)) end pockets, created by the assembly of three ligands around each Mn(5) subunit. Antiferromagnetic exchange dominates the spin coupling in the Mn(10) complexes, and surface studies on highly oriented pyrolytic graphite (HOPG) clearly show the arrangement of metal ions (Mn, Cs) in the Mn(10)Cs(2) linear cluster assembly.

Conformational control of TTFV π-frameworks through naphthyl substituents.

With 1- or 2-naphthyl substituted at the vinyl positions, the conformation of the tetrathiafulvalene vinylogue π-framework can be greatly modified from completely planar to highly twisted, and the structural changes lead to markedly different electronic and electrochemical behaviours.

1,2-Bis{4-[1-(anthracen-9-ylmeth-yl)-1H-1,2,3-triazol-4-yl]phen-yl}-1,2-bis-[4,5-bis-(methyl-sulfan-yl)-1,3-dithiol-2-yl-idene]ethane.

The title mol-ecule, C58H44N6S8, has point symmetry 2 (in the Schönfliess notation C2). The related crystallographic twofold axis bis-ects the central ethane bond while it is parallel to the monoclinic unique axis of the unit cell. The dithiole=C-C=dithiole torsion angle is 103.7 (4)° and the triazole-anthracene moieties adopt a pincer-like conformation. The crystal structure features C-H⋯S and C-H⋯N contacts. The distance between the stacked anthracene fragments [centroid-centroid separations of 3.6871 (19) Å, off-set by 1.516 (3) Šand mean anthracene plane-plane separations of 3.361 (2) Å], which are parallel to (101) and (-101), indicates inter-molecular anthracene-anthracene π-π contacts. One of the terminal methyl-sulfanyl groups was modelled as being disordered with two refined orientations that converged to occupancies of 0.809 (5) and 0.191 (5).