Ruthenium Water Oxidation Catalysts based on Pentapyridyl Ligands.

Ruthenium complexes containing the pentapyridyl ligand 6,6''-(methoxy(pyridin-2-yl)methylene)di-2,2'-bipyridine (L-OMe) of general formula trans-[Ru (X)(L-OMe-κ-N )] (X=Cl, n=1, trans-1 ; X=H O, n=2, trans-2 ) have been isolated and characterized in solution (by NMR and UV/Vis spectroscopy) and in the solid state by XRD. Both complexes undergo a series of substitution reactions at oxidation state Ru and Ru when dissolved in aqueous triflic acid-trifluoroethanol solutions as monitored by UV/Vis spectroscopy, and the corresponding rate constants were determined. In particular, aqueous solutions of the Ru -Cl complex trans-[Ru (Cl)(L-OMe-κ-N )] (trans-1 ) generates a family of Ru aquo complexes, namely trans-[Ru (H O)(L-OMe-κ-N )] (trans-2 ), [Ru (H O) (L-OMe-κ-N )] (trans-3 ), and [Ru (Cl)(H O)(L-OMe-κ-N )] (trans-4 ).

Ruthenium water oxidation catalysts containing the non-planar tetradentate ligand, biisoquinoline dicarboxylic acid (biqaH).

Two ruthenium complexes containing the tetradentate ligand [1,1'-biisoquinoline]-3,3'-dicarboxylic acid, and 4-picoline or 6-bromoisoquinoline as axial ligands have been prepared. The complexes have been fully characterised and initial studies on their potential to function as molecular water oxidation catalysts have been performed. Both complexes catalyse the oxidation of water in acidic media with Ce as a stoichiometric chemical oxidant, although turnover numbers and turnover frequencies are modest when compared with the closely related Ru-bda and Ru-pda analogues.

Supramolecular water oxidation with Ru-bda-based catalysts.

Extremely slow and extremely fast new water oxidation catalysts based on the Ru-bda (bda=2,2'-bipyridine-6,6'-dicarboxylate) systems are reported with turnover frequencies in the range of 1 and 900 cycles s(-1) , respectively. Detailed analyses of the main factors involved in the water oxidation reaction have been carried out and are based on a combination of reactivity tests, electrochemical experiments, and DFT calculations. These analyses give a convergent interpretation that generates a solid understanding of the main factors involved in the water oxidation reaction, which in turn allows the design of catalysts with very low energy barriers in all the steps involved in the water oxidation catalytic cycle.

A flow-system array for the discovery and scale up of inorganic clusters.

The batch synthesis of inorganic clusters can be both time consuming and limited by a lack of reproducibility. Flow-system approaches, now common in organic synthesis, have not been utilized widely for the synthesis of clusters. Herein we combine an automated flow process with multiple batch crystallizations for the screening and scale up of syntheses of polyoxometalates and manganese-based single-molecule magnets.

Integrated 3D-printed reactionware for chemical synthesis and analysis.

Three-dimensional (3D) printing has the potential to transform science and technology by creating bespoke, low-cost appliances that previously required dedicated facilities to make. An attractive, but unexplored, application is to use a 3D printer to initiate chemical reactions by printing the reagents directly into a 3D reactionware matrix, and so put reactionware design, construction and operation under digital control. Here, using a low-cost 3D printer and open-source design software we produced reactionware for organic and inorganic synthesis, which included printed-in catalysts and other architectures with printed-in components for electrochemical and spectroscopic analysis.

Solution-phase monitoring of the structural evolution of a Molybdenum Blue nanoring.

The inorganic host-guest complex Na(22){[Mo(VI)(36)O(112)(H(2)O)(16)]⊂[Mo(VI)(130)Mo(V)(20)O(442)(OH)(10)(H(2)O)(61)]}·180H(2)O ≡ {Mo(36)}⊂{Mo(150)}, compound 1, has been isolated in its solid crystalline state via unconventional synthesis in a custom flow reactor. Carrying out the reaction under controlled flow conditions selected for the generation of {Mo(36)}⊂{Mo(150)} as the major product, allowing it to be reproducibly isolated in a moderate yield, as opposed to traditional "one-pot" batch syntheses that typically lead to crystallization of the {Mo(36)} and {Mo(150)} species separately. Structural and spectroscopic studies of compound 1 and the archetypal Molybdenum Blue (MB) wheel, {Mo(150)}, identified compound 1 as a likely intermediate in the {Mo(36)} templated synthesis of MB wheels.

Osmotically driven crystal morphogenesis: a general approach to the fabrication of micrometer-scale tubular architectures based on polyoxometalates.

The process of osmotically driven crystal morphogenesis of polyoxometalate (POM)-based crystals is investigated, whereby the transformation results in the growth of micrometer-scale tubes 10-100 μm in diameter and many thousands of micrometers long. This process initiates when the crystals are immersed in aqueous solutions containing large cations and is governed by the solubility of the parent POM crystal. Evidence is presented that indicates the process is general to all types of POMs, with solubility of the parent crystal being the deciding parameter.

Fine tuning reactivity: synthesis and isolation of 1,2,3,12b-tetrahydroimidazo[1,2-f]phenanthridines.

A facile route for the synthesis and isolation of 1,2,3,12b-tetrahydroimidazo[1,2-f]phenanthridines (TIPs) has been developed. The heterocycle is a reactive intermediate in the three-step cascade synthesis of 2,3-dihydro-1H-imidazo[1,2-f]phenanthridinium cations (DIPs), a biologically active DNA intercalating framework; however, the intermediate has previously only been characterized in situ. Derivatization of the structure at the imidazo-N position controls the reactivity of the intermediate with respect to electronic potential and pK(a) allowing isolation of a selection of TIP structures.

A new C-C bond forming annulation reaction leading to pH switchable heterocycles.

A C-C bond forming reaction resulting from the alpha-addition of carbon based nucleophiles to N-bromoethyl phenanthridinium leads to the formation of 2,3-dihydro-12H-pyrrolo[1,2-f]phenanthridine-based derivatives which undergo reversible ring-opening/closing under pH control.

Realization of a "lockable" molecular switch via pH- and redox-modulated cyclization.

A switchable organic system involving four distinct states that can be interconverted by use of both pH and redox chemistry as control parameters has been developed. The key molecules involved in this system are the phenanthridine-based heterocycles 1-isobutyl-1,2,3,12b-tetrahydroimidazo[1,2-f]phenanthridine (TIP) and 5-[2-(isobutylamino)ethyl]phenanthridinium (AEP). These two states are interchangeable via pH control, and in addition they can also be further manipulated by oxidation or reduction to convert them to their "pH-inert" forms: 1-isobutyl-2,3-dihydro-1H-imidazo[1,2-f]phenanthridinium (DIP) and 5-[2-(isobutylamino)ethyl]-5,6-dihydrophenanthridine (AEDP), respectively.

A general and efficient five-step one-pot procedure leading to nitrogen-bridgehead heterocycles containing an imidazole ring.

A very simple annulation reaction was designed, allowing an imidazole moiety to be fused onto a range of pyridine-based derivatives. The methodology consists of an activation step via the formation of a pyridinium salt to increase the electrophilicity of the pyridine ring, followed by a cascade reaction triggered by a nucleophilic attack of the iminium moiety. Depending on the pyridinium salt, it is possible to obtain functionalized imidazole moieties.