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The first examples of a pi-conjugated benzo[b]phosphole P-oxide in which two phosphole P-oxide units are connected by a carbon-carbon double bond are described. The molecules are synthesized as E isomers with respect to the carbon-carbon double bond and exist as stable cis and trans isomers (chiral and meso one respectively) relatively to the two stereogenic P atoms. The optical and electrochemical properties of both isomers have been investigated by experiment and computations.

Molecular electrocatalysts for CO2-to-CO conversion often operate at large overpotentials, due to the large barrier for C-O bond cleavage. Illustrated with ruthenium polypyridyl catalysts, we herein propose a mechanistic route that involves one metal center that acts as both Lewis base and Lewis acid at different stages of the catalytic cycle, by density functional theory in corroboration with experimental FTIR. The nucleophilic character of the Ru center manifests itself in the initial attack on CO2 to form [Ru-CO2](0), while its electrophilic character allows for the formation of a 5-membered metallacyclic intermediate, [Ru-CO2CO2](0,c), by addition of a second CO2 molecule and intramolecular cyclization. The calculated activation barrier for C-O bond cleavage via the metallacycle is decreased by 34.9 kcal mol(-1) as compared to the non-cyclic adduct in the two electron reduced state of complex 1. Such metallacyclic intermediates in electrocatalytic CO2 reduction offer a new design feature that can be implemented consciously in future catalyst designs.

A biomimetic model complex of the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group has been synthesized, characterized and evaluated as catalyst for the light-driven hydrogen production. The interaction of the hydroxyl group present in the complex with 3-isocyanopropyltriethoxysilane provided a carbamate triethoxysilane bearing a diiron dithiolate complex (NCOFeFe), thus becoming a potentially promising candidate for anchoring on heterogeneous supports. As a proof of concept, the NCOFeFe precursor was anchored by a grafting procedure into a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Both molecular and heterogenized complexes were tested as catalysts for light-driven hydrogen generation in aqueous solutions. The photocatalytic conditions were optimized for the homogenous complex by varying the reaction time, pH, amount of the catalyst or photosensitizer, photon flux, and the type of light source (light-emitting diode (LED) and Xe lamp). It was shown that the molecular FeFeOH diiron complex achieved a decent turnover number (TON) of 70 after 6 h, while NCOFeFe and EthanePMO@NCOFeFe had slightly lower activities showing TONs of 37 and 5 at 6 h, respectively.

Cobalt polypyridyl complexes efficiently catalyze hydrogen evolution in aqueous media and exhibit high stability under reducing conditions. Their stability and activity can be tuned through electronic and steric considerations, but the rationalization of these effects requires detailed mechanistic understanding. As an example, tetradentate ligands with two non-permanently occupied coordination sites show higher activity with these sites in cis compared to trans configuration. Here reaction mechanisms of the Co-polypyridyl complex [Co-II(bpma)Cl-2] (bpma = bipyridinylmethyl-pyridinylmethyl-methyl-amine) have been studied using hybrid density-functional theory. This complex has two exchangeable cis sites, and provides a flexible ligand environment with both pyridyl and amine coordination. Two main pathways with low barriers are found. One pathway, which includes both open sites, is hydrogen evolution from a Co-II-H intermediate with a water ligand as the proton donor. In the second pathway H-H bond formation occurs between the hydride and the protonated bpma ligand, with one open site acting as a spectator. The two pathways have similar barriers at higher pH, while the latter becomes more dominant at lower pH. The calculations consider a large number of interconnected variables; protonation sites, isomers, spin multiplicities, and the identities of the open binding sites, as well as their combinations, thus exploring many simultaneous dimensions within each pathway. The results highlight the effects of having two open cis-coordination sites and how their relative binding affinities change during the reaction pathway. They also illustrate why Co-II-H intermediates are more active than Co-III-H ones, and why pyridyl protonation gives lower reaction barriers than amine protonation.

Procedures for the reductive coupling of carbonyl compounds to alkenes in the literature rely either on a radical coupling strategy, as in the McMurry coupling, or ionic pathways, sometimes catalysed by transition metals, as in more contemporary contributions. Herein, we present the first example of a third strategy that is based on the [2 + 2] cycloaddition of ketone-derived phosphaalkenes. Removal of P-trimethylsilyl groups at the intermediary 1,2-diphosphetane dimer results in its collapse and concomitant release of the tetraaryl-substituted alkene. In fact, the presented strategy is the only alternative to the McMurry coupling in the literature that allows tetraaryl alkene formation from diaryl ketones, with yields as high as 85%. The power of the methodology is illustrated in the reaction of tethered bis-benzophenones which engage in intramolecular reductive carbonyl couplings to form unusual macrocycles without the need for high dilution conditions or templating.

Current methodologies for the direct reductive coupling of two aldehydes to alkenes afford almost exclusively the thermodynamically favoured E-isomer. Recent efforts to find phosphorus-based reagents as replacements for the low-valent Ti species in McMurry couplings present opportunities to change this shortcoming, and to design new reagents that allow for the formation of high proportions of Z-alkenes under kinetic control. Here, we report the first example of such a reagent, a phosphanyl phosphonate Mes(F)P(H)P(O)(OEt)(2), 6, with an electron-deficient Mes(F)=2,4,6-(CF3)(3)Ph substituent that promotes the reductive homo-coupling of (hetero)aromatic aldehydes to alkenes with high Z-selectivity. Computational results indicate that the selectivity stems from the electron deficient Mes(F), which results in lowered activation barriers for the collapse of a cis-oxaphosphetane intermediate. In the absence of Mes(F), the E-isomer is exclusively observed experimentally. Directing the isomeric outcome of alkene formation by introducing electron withdrawing P-substituents bears resemblance to the Still-Gennari modification of the Horner-Wadsworth-Emmons reaction where perfluorinated ethoxy substituents in the former also lead to high proportions of the Z-isomer.

The growing field of MOF-catalyst composites often relies on postsynthetic modifications for the installation of active sites. In the resulting MOFs, the spatial distribution of the inserted catalysts has far-reaching ramifications for the performance of the system and thus needs to be precisely determined. Herein, we report the application of a scanning nuclear microprobe for accurate and nondestructive depth profiling of individual UiO-66 and UiO-67 (UiO = Universitetet i Oslo) single crystals. Initial optimization work using native UiO-66 crystals yielded a microbeam method which avoided beam damage,y while subsequent analysis of Zr/Hf mixed-metal UiO-66 crystals demonstrated the potential of the method to obtain high-resolution depth profiles. The microbeam method was further used to analyze the depth distribution of postsynthetically introduced organic moieties, revealing either core-shell or uniform incorporation can be obtained depending on the size of the introduced molecule, as well as the number of carboxylate binding groups. Finally, the spatial distribution of platinum centers that were postsynthetically installed in the bpy binding pockets of UiO-67-bpy (bpy = 5,5'dicarboxyy-2,2'-bipyridine) was analyzed by microbeam and contextualized. We expect that the method presented herein will be applicable for characterizing a wide variety of MOFs subjected to postsynthetic modifications and provide information crucial for their optimization as functional materials.

Photochemical hydrogen evolution from a UiO‐66‐incorporated Fe2(dcbdt)(CO)6 catalyst in conjunction with a ruthenium photosensitizer and an ascorbate donor ceases after a period of irradiation, but is restored after a 60 min. resting period in the dark. Control experiments show that neither product inhibition nor pore clogging is responsible for this surprising behaviour, and intra‐crystal linker scrambling is proposed as a potential explanation.

Understanding the structural features of molecular electrocatalysts for carbon dioxide reduction and water oxidation is essential for manufacturing next generation catalysts for renewable energy. We will discuss the crucial structural motifs of those catalysts that have shown novel characteristics in recent years in terms of electrocatalytic efficacy (high TON, TOF and low overpotential), product selectivity and mechanisms. Both inorganic and organic homogeneous catalysts are scrutinized in this review. We will also highlight electrocatalysts with dual activity (i.e. they are able to catalyze both water oxidation and CO2 reduction) as an interesting prospect from the point of view of a single catalyst electrolyzer: a possible design for future easy-to-manufacture effective electrolyzers. This discussion will enrich the overall knowledge on the electrocatalyst design, an important step towards the development of efficient catalysts with cutting edge designs for a renewable energy future and practical applications.

PhP(Li)TMS converts benzophenones to phosphaalkenes which upon activation under oxidizing, basic conditions react with aromatic aldehydes under the formation of triarylalkenes. The one-pot reaction omits transition metals, proceeds at room temperature and precludes the formation of any homo-coupling products. Systematic substrate variations reveal reactivity patterns that are useful for the identification of ketone/aldehyde combinations that can be coupled in yields up to 80%.

Molecular hydrogen evolution catalysts (HECs) are synthetically tunable and often exhibit high activity, but they are also hampered by stability concerns and practical limitations associated with their use in the homogeneous phase. Their incorporation as integral linker units in metal-organic frameworks (MOFs) can remedy these shortcomings. Moreover, the extended three-dimensional structure of MOFs gives rise to high catalyst loadings per geometric surface area. Herein, we report a new MOF that exclusively consists of cobaloximes, a widely studied HEC, that act as metallo-linkers between hexanuclear zirconium clusters. When grown on conducting substrates and under applied reductive potential, the cobaloxime linkers promote electron transport through the film as well as function as molecular HECs. The obtained turnover numbers are orders of magnitude higher than those of any other comparable cobaloxime system, and the molecular integrity of the cobaloxime catalysts is maintained for at least 18 h of electrocatalysis. Being one of the very few hydrogen evolving electrocatalytic MOFs based on a redox-active metallo-linker, this work explores uncharted terrain for greater catalyst pathways.

[FeFe(Cl-2-bdt)(CO)(6)] (1; Cl-2-bdt=3,6-dichlorobenzene-1,2-dithiolate), inspired by the active site of FeFe-hydrogenase, shows a chemically reversible 2 e(-) reduction at -1.20 V versus the ferrocene/ferrocenium couple. The rigid and aromatic bdt bridging ligand lowers the reduction potential and stabilizes the reduced forms, compared with analogous complexes with aliphatic dithiolates; thus allowing details of the catalytic process to be characterized. Herein, time-resolved IR spectroscopy is used to provide kinetic and structural information on key catalytic intermediates. This includes the doubly reduced, protonated complex 1H(-), which has not been previously identified experimentally. In addition, the first direct spectroscopic observation of the turnover process for a molecular H-2 evolving catalyst is reported, allowing for straightforward determination of the turnover frequency.

This account highlights the versatility of phosphanylphosphonates, which can be used for the preparation of phosphorus-containing π-systems and as reagents for the reductive coupling of carbonyl compounds to alkenes. Phosphanylphosphonates with metal fragments coordinated to the P-lone pair have been known for a long time and they have been used for the synthesis of phosphaalkenes by means of the phospha-Horner–Wadsworth–Emmons reaction. With the original aim of incorporating phosphorus heteroatoms into classical all-carbon ethynylethene scaffolds, we entered the field of phosphanylphosphonates with the discovery that these compounds engage in complex cascade reactions with acetylenic ketones, forming 1,2-oxaphospholes, cumulenes, and bisphospholes. Later, we synthesized the first metal-free phosphanylphosphonate, which reacts with aldehydes to yield phosphaalkenes, but gives phospholones when diacetylenic ketones are used as substrates. In the final part of the account, we outline our discovery and the development of an unprecedented carbonyl–carbonyl cross-coupling reaction. This protocol offers a straightforward method for the synthesis of nonsymmetric 1,2-disubstituted alkenes directly from two dissimilar aldehydes. 1. Combining Acetylenes with Phosphaalkenes 2. Synthetic Examples of Acetylenic Phosphaalkenes 3. The Phospha-Horner–Wadsworth–Emmons Approach to Phosphaalkenes 3.1. Metal-Coordinated Phosphanylphosphonates 3.2. Mechanism of the Phospha-Horner–Wadsworth–Emmons Reaction 3.3. The First Metal-Free Phosphanylphosphonate and Its Reactivity with Aldehydes 4. Reactions with Acetylenic Ketones 4.1. Metal-Coordinated Phosphanylphosphonate and Monoacetylenic Ketones 4.2. Metal-Coordinated Phosphanylphosphonate and Diacetylenic Ketones 4.3. Metal-Free Phosphanylphosphonate and Diacetylenic Ketones 5. Metal-Free Phosphanylphosphonate as a Coupling Reagent for Aldehydes 6. E-Alkenes by the Reductive Coupling of Two Aldehydes 7. Conclusions and Outlook

A new series of homodinuclear iron complexes as models of the [FeFe]-hydrogenase active site was prepared and characterized. The complexes of the general formula [Fe-2(mcbdt)(CO)(5)PPh2R] (mcbdt = benzene-1,2-dithiol-3-carboxylic acid) feature covalent tethers that link the mcbdt ligand with the phosphine ligands which are terminally coordinated to one of the Fe centres. The synthetic feasability of the concept is demonstrated with the preparation of three novel complexes. A detailed theoretical investigation showes that by introducing a rigid covalent link between the phosphine and the bridging dithiolate ligands, the rotation of the Fe(CO)(2)P unit is hindered and higher rotation barriers were calculated compared to non-linked reference complexes. The concept of restricting Fe(L)(3) rotation is an approach to kinetically stabilize terminal hydrides which are reactive intermediates in catalytic proton reduction cycles of the enzymes.

Self-assembly of carboxylic-acid-functionalized dyes on mesoporous, anatase TiO2 is at the heart of dye-sensitized solar cells (DSSCs). However, the process often requires 6-20 h of electrode immersion at room temperature in the dye-bath solutions. Here, we introduce a new, rapid microwave-assisted sensitization technique (MINAS), which significantly accelerates the sensitization process and yields high-quality, self-assembled films of an organic dye within 5 min. Targeted experiments show that the effects of the microwave radiation cannot be explained purely on the basis of the thermal component. The interaction of the microwave radiation with the conductive fluorine-doped tin oxide (FTO) electrical contact is a key aspect to consider and a unique feature of MWAS that is the likely cause for producing rapid self-assembly of the dye on the surface.

The phospha-Peterson reaction between a lithiated secondary phosphane, MesP(Li)TMS, and an aldehyde affords Mes-phosphaalkenes which, upon methanol addition and P-oxidation, react with a second carbonyl compound site specifically to produce unsymmetric alkenes. The E/Z selectivity of the one-pot cross coupling is largely determined by the electronic nature of the aryl substituent of the first aldehyde, with electron-donating groups giving rise to increased amounts of Z-alkenes.

Meeting Abstract: 1173

Metal–organic frameworks (MOFs) as electrocatalysis scaffolds are appealing due to the large concentration of catalytic units that can be assembled in three dimensions. To harness the full potential of these materials, charge transport to the redox catalysts within the MOF has to be ensured. Herein, we report the first electroactive MOF with the UiO/PIZOF topology (Zr(dcphOH-NDI)), i.e., one of the most widely used MOFs for catalyst incorporation, by using redox-active naphthalene diimide-based linkers (dcphOH-NDI). Hydroxyl groups were included on the dcphOH-NDI linker to facilitate proton transport through the material. Potentiometric titrations of Zr(dcphOH-NDI) show the proton-responsive behavior via the −OH groups on the linkers and the bridging Zr-μ3-OH of the secondary building units with pKa values of 6.10 and 3.45, respectively. When grown directly onto transparent conductive fluorine-doped tin oxide (FTO), 1 μm thin films of Zr(dcphOH-NDI)@FTO could be achieved. Zr(dcphOH-NDI)@FTO displays reversible electrochromic behavior as a result of the sequential one-electron reductions of the redox-active NDI linkers. Importantly, 97% of the NDI sites are electrochemically active at applied potentials. Charge propagation through the thin film proceeds through a linker-to-linker hopping mechanism that is charge-balanced by electrolyte transport, giving rise to cyclic voltammograms of the thin films that show characteristics of a diffusion-controlled process. The equivalent diffusion coefficient, De, that contains contributions from both phenomena was measured directly by UV/vis spectroelectrochemistry. Using KPF6 as electrolyte, De was determined to be De(KPF6) = (5.4 ± 1.1) × 10–11 cm2 s–1, while an increase in countercation size to n-Bu4N+ led to a significant decrease of De by about 1 order of magnitude (De(n-Bu4NPF6) = (4.0 ± 2.5) × 10–12 cm2 s–1).

The molecular water oxidation catalyst [Ru(bda)(L)(2)] has been incorporated into pyridine-decorated MIL-101(Cr) metal-organic frameworks. The resulting MIL-101@Ru materials exhibit turnover frequencies (TOFs) up to ten times higher compared to the homogenous reference. An unusual dependence of the formal TOFs on oxidant concentration is observed that ultimately arises from differing amounts of catalysts in the MOF crystals being active., De två första författarna delar förstaförfattarskapet.

Metal hydrides are key intermediates in catalytic proton reduction and dihydrogen oxidation. There is currently much interest in appending proton relays near the metal centre to accelerate catalysis by proton-coupled electron transfer (PCET). However, the elementary PCET steps and the role of the proton relays are still poorly understood, and direct kinetic studies of these processes are scarce. Here, we report a series of tungsten hydride complexes as proxy catalysts, with covalently attached pyridyl groups as proton acceptors. The rate of their PCET reaction with external oxidants is increased by several orders of magnitude compared to that of the analogous systems with external pyridine on account of facilitated proton transfer. Moreover, the mechanism of the PCET reaction is altered by the appended bases. A unique feature is that the reaction can be tuned to follow three distinct PCET mechanisms-electron-first, proton-first or a concerted reaction-with very different sensitivities to oxidant and base strength. Such knowledge is crucial for rational improvements of solar fuel catalysts.

Stilbenes with push-pull electronics are directly accessible from an electron-rich and an electron-deficient benzaldehyde in a novel reductive aldehyde cross-coupling reaction. The one-pot procedure is enabled by the oxidation of a transient phosphinite to the corresponding phosphinate which exhibits sufficient reactivity towards deactivated aldehydes.

A series of bis-tridentate ruthenium complexes was designed to feature opposite localizations of their lowest metal-to-ligand charge transfer (MLCT) excited states, relative to a carboxylic acid that served as a binding group to mesoporous NiO. The purpose was to study the effect of MLCT direction on the rates of hole injection into NiO and subsequent charge recombination. Surprisingly, femtosecond-transient absorption spectroscopy showed that the two heteroleptic, cyclometalated complexes of this series did not inject holes into NiO, but their excited states were nevertheless quenched in a rapid process (on the time scale of hundreds of picoseconds). An identical result was obtained for the dyes on nonreactive ZrO2 and we therefore attribute the short MLCT lifetime to self-quenching, due the high surface concentrations of the dyes. We further show that self-quenching on this time scale can potentially compete with hole injection also for functional NiO sensitizers. A ruthenium polypyridine complex, which has previously been used for NiO-based solar cells, was shown to inject holes only very slowly (τ ≈ 5 ns), in contrast to the common notion that hole injection in dye-NiO systems is ultrafast (predominantly subpicosecond time scale). The hole injection yield was estimated to only ca. 20%, which matches the reported APCE value of the corresponding device [Freys, J. C.; Gardner, J. M.; D’Amario, L.; Brown, A. M.; Hammarström, L. Dalton Trans. 2012, 41, 13105]. Therefore, we suggest that slow injection and self-quenching might be a reason for the low photovoltaic performance of some p-type dye-sensitized solar cells.

Co-sensitization of molecular dyes and catalysts on semiconductor surfaces is a promising strategy to build photoelectrodes for solar fuel production. In such a photoelectrode, understanding the charge transfer reactions between the molecular dye, catalyst and semiconductor material is key to guide further improvement of their photocatalytic performance. Herein, femtosecond mid-infrared transient absorption spectroscopy is used, for the first time, to probe charge transfer reactions leading to catalyst reduction on co-sensitized nickel oxide (NiO) photocathodes. The NiO films were co-sensitized with a molecular dye and a proton reducing catalyst from the family of [FeFe](bdt)(CO)(6) (bdt = benzene-1,2-dithiolate) complexes. Two dyes were used: an organic push-pull dye denoted E2 with a triarylamine-oligothiophene-dicyanovinyl structure and a coumarin 343 dye. Upon photo-excitation of the dye, a clear spectroscopic signature of the reduced catalyst is observed a few picoseconds after excitation in all co-sensitized NiO films. However, kinetic analysis of the transient absorption signals of the dye and reduced catalyst reveal important mechanistic differences in the first reduction of the catalyst depending on the co-sensitized molecular dye (E2 or C343). While catalyst reduction is preceded by hole injection in NiO in C343-sensitized NiO films, the singly reduced catalyst is formed by direct electron transfer from the excited dye E2* to the catalyst in E2-sensitized NiO films. This change in mechanism also impacts the lifetime of the reduced catalyst, which is only ca. 50 ps in E2-sensitized NiO films but is >5 ns in C343-sensitized NiO films. Finally, the implication of this mechanistic study for the development of better co-sensitized photocathodes is discussed.

A cobaloxime H-2 evolution catalyst with a hydroxo-functionalized pyridine ligand, Co(dmgH)(2)(4-HEP)Cl [dmgH = dimethylglyoxime, 4-HEP = 4-(2-hydroxyethyl)pyridine] was immobilized on a chromium terephthalate metal-organic framework (MOF), MIL-101(Cr), to construct a MOF-catalyst hybrid which displays good photocatalytic H-2 evolution activity. The longevity of the cobaloxime catalyst is increased by MOF incorporation, but limited by the stability of the cobalt-pyridine bond under turnover conditions.

Herein, we report a nano-hybrid photo-system based on abundant elements for H2 production with visible light. The photo-system's proficiency relates to the novel ZnO nanocrystals employed. The ZnO carboxylate oligoethylene glycol shell enhances charge separation and accumulates reactive electrons for the photocatalytic process.

A molecular water oxidation catalyst, [Ru(tpy)(dcbpy)(OH2)](ClO4)(2) (tpy = 2,2': 6',2''-terpyridine, dcbpy = 2,2'-bipyridine- 5,5'-dicarboxylic acid) [1], has been incorporated into FTO-grown thin films of UiO-67 (UiO = University of Oslo), by post-synthetic ligand exchange. Cyclic voltammograms (0.1 M borate buffer at pH = 8.4) of the resulting UiO67-[RuOH2]@ FTO show a reversible wave associated with the Ru-III/II couple in the anodic scan, followed by a large current response that arises from electrocatalytic water oxidation beyond 1.1 V vs. Ag/AgCl. Water oxidation can be observed at an applied potential of 1.5 V over the timescale of hours with a current density of 11.5 mu A cm(-2). Oxygen evolution was quantified in situ over the course of the experiment, and the Faradaic efficiency was calculated as 82%. Importantly, the molecular integrity of [1] during electrocatalytic water oxidation is maintained even on the timescale of hours under turnover conditions and applied voltage, as evidenced by the persistence of the wave associated with the Ru-III/II couple in the CV. This experiment highlights the capability of metal organic frameworks like UiO-67 to stabilize the molecular structure of catalysts that are prone to form higher clusters in homogenous phase.

Herein, we report three IrIIICp* complexes with hydroxy- or amino-functionalized N-heterocyclic carbene (NHC) ligands that catalyze efficient water oxidation induced by addition of ceric ammonium nitrate (CAN). The pendant hydroxy or amino groups are very important for activity, and the complexes with heteroatom-functionalized NHC ligands show up to 15 times higher rates of oxygen evolution in CAN-induced water oxidation than a reference IrIIICp* complex without heteroatom functionalization. The formation of molecular high-valent Ir intermediates that are presumably involved in the rate-determining step for water oxidation is established by UV/Vis spectroscopy and ESI-MS under turnover conditions. The hydroxy groups on the NHC ligands, as well as chloride ligands on the iridium center are proposed to structurally stabilize the high-valent species, and thereby improve the catalytic activity. The IrIII complex with a hydroxy-functionalized NHC shows the highest catalytic activity with a TON of 2500 obtained in 3 h and with ~90 % yield relative to the amount of oxidant used., Export Date: 11 December 2017; Article

Zirconium-oxide based metal-organic frameworks (MOFs) were grown on p-type Si wafers. A modified linker molecule containing iodine was introduced by post synthetic exchange (PSE). Samples have been studied using Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE) techniques, employing the 5 MV 15SDH-2 Pelletron Tandem accelerator at the Angstrom laboratory. The degree of post synthetic uptake of the iodine-containing linker has been investigated with both a broad beam and a focused beam of carbon and alpha particles targeting different kind of MOF crystals which were of similar to 1-10 mu m in size, depending on the linker used. Iodine concentrations in MOF crystallites were also measured by Nuclear Magnetic Resonance Spectroscopy (NMR) and are compared to the RBS results. In parallel to the ion beam studies, samples were investigated by Scanning Electron Microscopy (SEM) to quantify possible crystallite clustering, develop optimum sample preparation routines and to characterize the potential ion beam induced sample damage and its dependence on different parameters. Based on these results the reliability and accuracy of ion beam data is assessed.

The unprecedented formation of unsymmetrical alkenes from the intermolecular reductive coupling of two different aldehydes is described. In contrast to the McMurry reaction which affords statistical product mixtures, selectivity in the reported procedure is achieved by a sequential ionic mechanism in which a first aldehyde is reacted with a phosphanylphosphonate to afford a phosphaalkene intermediate which, upon activation by hydroxide, reacts with a second aldehyde to the unsymmetrical E-alkenes. The described reaction is free of transition metals and proceeds under ambient temperature within minutes in good to excellent overall yields. It is a new methodology to use feedstock aldehydes for the direct production of C=C double bond-containing products and may impact how chemists think of multistep synthetic sequences in the future.

A series of novel cyclometalated Ru-II complexes were investigated featuring the tridentate dqp ligand platform (dqp is 2,6-di(quinolin-8-yl)pyridine), in order to utilize the octahedral coordination mode around the Ru center to modulate the electrochemical and photophysical properties. The heteroleptic complexes feature C-1 symmetry due to symmetry breaking by the peripheral five- or six-membered carbanionic chelate (phenyl, naphthyl, or anthracenyl units). The chelation mode is controlled by the steric effects and C-H activation selectivity of the ligand, which prompted the development of a general synthesis protocol. The optimized conditions to achieve high overall yields (55-75%) involve NaHCO3 as the base and an simplified purification protocol: i.e., facile chromatographic separation using commercially available amino-functionalized silica applying nonaqueous salt-free conditions to omit the necessity of counterion exchange. The structural, photophysical, and electrochemical properties were studied in depth, and the results were corroborated by density functional theory (DFT) calculations. Steady state and time-resolved spectroscopy revealed red-shifted absorption (up to 750 run) and weak IR emission (800-1000 nm) combined with prolonged emission lifetimes (up to 20 ns) in comparison to classical tpy-based (tpy is 2,2':6',2 ''-terpyridine) complexes. An enhanced stability was observed by blocking the reactive positions of the carbanionic ligand framework, while the reactive positions may be exploited for further functionalization., Title in WoS: Asymmetric Cyclometalated Ru-II Polypyridyl-Type Complexes with pi-Extended Carbanionic Donor Sets

The distance dependence of concerted proton-coupled electron transfer (PCET) reactions was probed in a series of three new compounds, where a phenol is covalently bridged by a 5, 6, or 7 membered carbocycle to the quinoline. The carbocycle bridge enforces the change in distance between the phenol oxygen (proton donor) and quinoline nitrogen (proton acceptor), d(O center dot center dot center dot N), giving rise to values ranging from 2.567 to 2.8487 angstrom, and resulting in calculated proton tunneling distances, r(0), that span 0.719 to 1.244 angstrom. Not only does this series significantly extend the range of distances that has been previously accessible for experimental distance dependent PCET studies of synthetic model compounds, but it also greatly improves the isolation of d(O center dot center dot center dot N) as a variable compared to earlier reports. Rates of PCET were determined by time-resolved optical spectroscopy with flash-quench generated [Ru(bpy)(3)](3+) and [Ru(dce)(3)](3+), where bpy = 2,2'-bipyridyl and dce = 4,4'-dicarboxyethylester-2,2'-bipyridyl. The rates increased as d(O center dot center dot center dot N) decreased, as can be expected from a static proton tunneling model. An exponential attenuation of the PCET rate constant was found: k(PCET)(d) = k(PCET)(0)exp[-beta(d-d(0))], with beta similar to 10 angstrom(-1). The observed kinetic isotope effect (KIE = k(H)/k(D)) ranged from 1.2 to 1.4, where the KIE was observed to decrease slightly with increasing d(O center dot center dot center dot N). Both beta and KIE values are significantly smaller than what is predicted by a static proton tunneling model. We conclude that vibrational compression of the tunneling distances, as well as higher vibronic transitions, that contribute to concerted proton coupled electron transfer must also be considered.

A molecular H2-evolving catalyst, [Fe2(cbdt)(CO)6] ([FeFe], cbdt = 3-carboxybenzene-1,2-dithiolate), has been attached covalently to an amino-functionalized MIL-101(Cr) through an amide bond. Chemical reduction experiments reveal that the MOF channels can be clogged by ion pairs that are formed between the oxidized reductant and the reduced catalyst. This effect is lessened in MIL-101-NH-[FeFe] with lower [FeFe] loadings. On longer timescales, it is shown that large proportions of the [FeFe] catalysts within the MOF engage in photochemical hydrogen production and the amount of produced hydrogen is proportional to the catalyst loading.

Rutherford backscattering spectrometry (RBS) has been used for the first time to study post-synthetic linker exchange (PSE) in metal-organic frameworks. RBS is a non-invasive method to quantify the amount of introduced linker, as well as providing a means for depth profiling in order to identify the preferred localization of the introduced linker. The exchange of benzenedicarboxylate (bdc) by similarly sized 2-iodobenzenedicarboxylate (I-bdc) proceeds considerably slower than migration of I-dbc through the UiO-66 crystal. Consequently, the I-bdc is found evenly distributed throughout the UiO-66 samples, even at very short PSE exposure times.

Synthetic diiron compounds of the general formula Fe-2(mu-S2R)(CO)(n)(L)(6-n) (R = alkyl or aromatic groups; L = CN- or phosphines) are versatile models for the active-site cofactor of hydrogen turnover in [FeFe]-hydrogenases. A series of 18 diiron compounds, containing mostly a dithiolate bridge and terminal ligands of increasing complexity, was characterized by X-ray absorption and emission spectroscopy in combination with density functional theory. Fe K-edge absorption and K beta main-line emission spectra revealed the varying geometry and the low-spin state of the Fe(I) centers. Good agreement between experimental and calculated core-to-valence-excitation absorption and radiative valence-to-core-decay emission spectra revealed correlations between spectroscopic and structural features and provided access to the electronic configuration. Four main effects on the diiron core were identified, which were preferentially related to variation either of the dithiolate or of the terminal ligands. Alteration of the dithiolate bridge affected mainly the Fe-Fe bond strength, while more potent donor substitution and ligand field asymmetrization changed the metal charge and valence level localization. In contrast, cyanide ligation altered all relevant properties and, in particular, the frontier molecular orbital energies of the diiron core. Mutual benchmarking of experimental and theoretical parameters provides guidelines to verify the electronic properties of related diiron compounds.

The development of a reliable platform for the electrochemical characterization of a redox-active molecular diiron complex, [FeFe], immobilized in a non-conducting metal organic framework (MOF), UiO-66, based on glassy-carbon electrodes is reported. Voltammetric data with appreciable current responses can be obtained by the use of multiwalled carbon nanotubes (MWCNT) or mesoporous carbon (CB) additives that function as conductive scaffolds to interface the MOF crystals in "three-dimensional" electrodes. In the investigated UiO-66-[FeFe] sample, the low abundance of [FeFe] in the MOF and the intrinsic insulating properties of UiO-66 prevent charge transport through the framework, and consequently, only [FeFe] units that are in direct physical contact with the electrode material are electrochemically addressable.

The reactivity of [Fe-2(dcbdt)(CO)(6)] (1) confined in a UiO-66(Zr) metal-organic framework towards CO ligand substitutions with phosphines of different sizes was investigated. The reaction with smaller phosphines (PX3, X = Me, Et) is more selective compared to analogous reactions in homogenous solution phase, and two CO ligands at up to 80% of all [FeFe] sites in UiO-66-1 are replaced. The produced [Fe-2(dcbdt)(CO)(4)(PX3)(2)] complexes in the UiO-66 matrix behave like typical [FeFe] hydrogenase active site model complexes, are reduced at more cathodic potentials than their hexacarbonyl analogues, and form bridging hydrides under acidic conditions.

Mesoporous NiO films were cosensitized with a coumarin 343 dye and a proton reduction catalyst of the [Fe-2(CO)(6)(bdt)] (bdt = benzene-1,2-dithiolate) family. Femtosecond ultraviolet visible transient absorption experiments directly demonstrated subpicosecond hole injection into NiO from excited dyes followed by rapid (t(50%) similar to 6 ps) reduction of the catalyst on the surface with similar to 70% yield. The reduced catalyst was long-lived (2 mu s to 20 ms), which may allow protonation and a second reduction step of the catalyst to occur. A photo electrochemical device based on this photocathode produced H-2 with a Faradaic efficiency of similar to 50%. Fourier transform infrared spectroscopy and gas chromatography experiments demonstrated that the observed device deterioration with time was mainly due to catalyst degradation and desorption from the NiO surface. The insights gained from these mechanistic studies, regarding development of dye-catalyst cosensitized photocathodes, are discussed.

A series of Ru-II polypyridyl complexes of the structural design [Ru-II(R-tpy)(NN)(CH3CN)](2+) (R-tpy= 2,2': 6', 2''-terpyridine (R= H) or 4,4', 4''-tri-tert-butyl-2,2': 6', 2''-terpyridine (R= tBu); NN= 2,2'-bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO2 to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes' reactivities. Whereas electron-donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru-II(tpy)(6-mbpy)(CH3CN)](2+) (trans-[3](2+); 6-mbpy= 6-methyl- 2,2'-bipyridine) and [Ru-II(tBu-tpy)(6-mbpy)(CH3CN)](2+) (trans-[4](2+)), in which the methyl group of the 6-mbpy ligand is trans to the CH3CN ligand, show electrocatalytic CO2 reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer-chemical reaction-electron transfer), and is a direct result of steric interactions that facilitate CH3CN ligand dissociation, CO2 coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru(tBu(3)tpy)(bpy)(NCCH3)](2+) (tBu(3)tpy = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine; bpy = 2,2'-bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO2 to CO. The methyl group enables CO2 binding already at the one-electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO2 reduction catalysts.

The first direct alkynylation of C,C-dibromophosphaalkenes by a reaction with sulfonylacetylenes is reported. Alkynylation proceeds selectively in the trans position relative to the P substituent to afford bromoethynylphosphaalkenes. Owing to the absence of transition metals in the procedure, the previously observed conversion of dibromophosphaalkenes into phosphaalkynes through the phosphorus analog of the Fritsch-Buttenberg-Wiechell rearrangement is thus suppressed. The bromoethynylphosphaalkenes can subsequently be converted to C,C-diacetylenic, cross-conjugated phosphaalkenes by following a Sonogashira coupling protocol in good overall yields. By using the newly described method, full control over the stereochemistry at the P=C double bond is achieved. The substrate scope of this reaction is demonstrated for different dibromophosphaalkenes as well as different sulfonylacetylenes.

The synthesis of the first phophanylphosphonate, Mes*PH-PO(OEt)(2) (2-H), in which the P(III) centre is not coordinated by a M(CO)(5) (M = W, Mo, Cr) fragment is reported. The title compound reacts with LDA under the formation of 2-Li which is best described as the enolate form with a high double bond character between the two phosphorus centres. 2-Li is shown to engage in the phospha-Wittig-Horner reaction and converts aldehydes into phosphaalkenes that are metal-free and thus available for future manipulations at the phophorus lone pair. Using a selection of aldehydes with aliphatic, aromatic or vinylic substituents as substrates, phosphaalkene formation proceeds in high yields and high E-selectivity. The selectivity is however compromised during purification on standard silica which was found to promote E/Z isomerization.

The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)(6) (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (tau approximate to 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t(1/2) approximate to 10 ps) and efficient surface electron transfer from C343 to the coadsorbed [FeFe] (mcbdt)(CO)(6). The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on. DSSFDs.

The development of molecular water oxidation catalysts basedon earth-abundant, non-noble metals is essential for artificial photosynthesis research. Iron, which is the most abundant transition metal in the earth's crust, is a prospective candidate for this purpose. Herein, we report two iron complexes based on the polypyridyl ligand Py5OH (Py5OH=pyridine-2,6-diylbis[di(pyridin-2-yl)methanol]) that can catalyse water oxidation to produce O2 in RuIII-induced (at pH 8, highest turnover number (TON)=26.5; turnover frequency (TOF)=2.2 s-1), CeIV-induced(at pH 1.5 highest TON=16; TOF=0.75 s-1) and photo-induced(at pH 8, highest TON=43.5; TOF=0.6 s-1) reactions. A chloride ligand in one of the iron complexes is shown to affect the activity strongly, improve stability and, thereby, the performance at pH 8 but it inhibits oxygen evolution at pH 1.5. The observations are consistent with a change in mechanism for catalytic water oxidation with the Fe(Py5OH) complexes between acidic (CeIV) and near-neutral pH (RuIII).

Versatile synthetic protocols for 2,7- and 3,6-diacetylenic fluorene-9-ylidene phosphanes (F9Ps) were developed. Protodesilylation of trimethylsilyl-protected acetylenic F9Ps affords terminal acetylenes that can be employed in Sonogashira and Glaser-type C-C coupling reactions to give thienyl-decorated and butadiyne-bridged fluorene-9-ylidene phosphanes, respectively. As evidenced by UV/Vis spectroscopy and cyclic voltammetry and corroborated by ab initio calculations, the presence of the P center in the F9Ps induces a significantly reduced HOMO-LUMO splitting that originates from stabilization of the LUMO levels. Variation of the acetylene substitution pattern is an additional tool to influence the optical and electronic properties. Whereas 3,6-disubstituted F9Ps have strong absorptions around 400nm, mainly due to -* transitions, 2,7-diacetylenic F9Ps exhibit longest-wavelength absorptions that have significant charge-transfer character with an onset around 520nm.

A new efficient organic dye LEG4F, incorporating a fluorine-substituted phenylene unit in the π-spacer, has been synthesized and tested in dye-sensitized solar cells. Direct comparison with the parent dye LEG4 shows very similar performances in case of liquid electrolyte devices based on iodide/triiodide, yielding a power conversion efficiency of 6.8% under 1 sun and 8.0–8.2% under 0.5 sun illumination. However, LEG4F outperforms its fluorine-free analogue when the liquid electrolyte is replaced by the solid-state hole-transport material Spiro-OMeTAD, reaching 5.3% efficiency compared to 4.8% achieved by LEG4. We show that this improvement is due to the enhancement of the electron lifetime, which reduces recombination at the TiO2/dye/Spiro-OMeTAD interfaces.