Crystal structure elucidation of a geminal and vicinal bis(trifluoromethanesulfonate) ester.

Geminal and vicinal bis(trifluoromethanesulfonate) esters are highly reactive alkylene synthons used as potent electrophiles in the macrocyclization of imidazoles and the transformation of bypyridines to diquat derivatives via nucleophilic substitution reactions. Herein we report the crystal structures of methylene (C3H2F6O6S2) and ethylene bis(trifluoromethanesulfonate) (C4H4F6O6S2), the first examples of a geminal and vicinal bis(trifluoromethanesulfonate) ester characterized by single-crystal X-ray diffraction (SC-XRD). With melting points slightly below ambient temperature, both reported bis(trifluoromethanesulfonate)s are air- and moisture-sensitive oils and were crystallized at 277 K to afford two-component non-merohedrally twinned crystals. The dominant interactions present in both compounds are non-classical C-H...O hydrogen bonds and intermolecular C-F...F-C interactions between trifluoromethyl groups. Molecular electrostatic potential (MEP) calculations by DFT-D3 helped to quantify the polarity between O...H and F...F contacts to rationalize the self-sorting of both bis(trifluoromethanesulfonate) esters in polar (non-fluorous) and non-polar (fluorous) domains within the crystal structure.

Metals in Cancer Research: Beyond Platinum Metallodrugs.

The discovery of the medicinal properties of platinum complexes has fueled the design and synthesis of new anticancer metallodrugs endowed with unique modes of action (MoA). Among the various families of experimental antiproliferative agents, organometallics have emerged as ideal platforms to control the compounds' reactivity and stability in a physiological environment. This is advantageous to efficiently deliver novel prodrug activation strategies, as well as to design metallodrugs acting only via noncovalent interactions with their pharmacological targets. Noteworthy, another justification for the advance of organometallic compounds for therapy stems from their ability to catalyze bioorthogonal reactions in cancer cells. When not yet ideal as drug leads, such compounds can be used as selective chemical tools that benefit from the advantages of catalytic amplification to either label the target of interest (e.g., proteins) or boost the output of biochemical signals. Examples of metallodrugs for the so-called "catalysis in cells" are considered in this Outlook together with other organometallic drug candidates. The selected case studies are discussed in the frame of more general challenges in the field of medicinal inorganic chemistry.

Enhancing Flavins Photochemical Activity in Hydrogen Atom Abstraction and Triplet Sensitization through Ring-Contraction.

The isoalloxazine heterocycle of flavin cofactors reacts with various nucleophiles to form covalent adducts with important functions in enzymes. Molecular flavin models allow for the characterization of such adducts and the study of their properties. A fascinating set of reactions occurs when flavins react with hydroxide base, which leads to imidazolonequinoxalines, ring-contracted flavins, with so far unexplored activity. We report a systematic study of the photophysical properties of this new chromophore by absorption and emission spectroscopy as well as cyclic voltammetry. Excited, ring-contracted flavins are significantly stronger hydrogen atom abstractors when compared to the parent flavins, which allowed the direct trifluoromethylthiolation of aliphatic methine positions (bond dissociation energy (BDE) of 400.8 kJ mol-1). In an orthogonal activity, their increased triplet energy (E(S0←T1)=244 kJ mol-1) made sensitized reactions possible which exceeded the power of standard flavins. Combining both properties, ring-contracted flavin catalysts enabled the one-pot, five-step transformation of α-tropolone into trans-3,4-disubstituted cyclopentanones. We envision this new class of flavin-derived chromophores to open up new modes of reactivity that are currently impossible with unmodified flavins.

Benzene-1,4-Di(dithiocarboxylate) Linker-Based Coordination Polymers of Mn2+, Zn2+, and Mixed-Valence Fe2+/3.

Three new coordination polymers (CPs) constructed from the linker 1,4-di(dithiocarboxylate) (BDDTC2-)─the sulfur-analog of 1,4-benzenedicarboxylate (BDC2-)─together with Mn-, Zn-, and Fe-based inorganic SBUs are reported with description of their structural and electronic properties. Single-crystal X-ray diffraction revealed structural diversity ranging from one-dimensional chains in [Mn(BDDTC)(DMF)2] (1) to two-dimensional (2D) honeycomb sheets observed for [Zn2(BDDTC)3][Zn(DMF)5(H2O)] (2). Gas adsorption experiments confirmed a 3D porous structure for the mixed-valent material [Fe2(BDDTC)2(OH)] (3). 3 contains a 1:1 ratio of Fe2+/3+ ions, as evidenced by 57Fe Mössbauer, X-band EPR, and X-ray absorption spectroscopy. Its empirical formula was established by elemental analysis, thermal gravimetric analysis, infrared vibrational spectroscopy, and X-ray absorption spectroscopy in lieu of elusive single-crystal X-ray diffraction data. In contrast to the Mn- and Zn-based compounds 1 and 2, the Fe2+/3+ CP 3 showed remarkably high electrical conductivity of 5 × 10-3 S cm-1 (according to van der Pauw measurements), which is within the range of semiconducting materials. Overall, our study confirms that sulfur derivatives of typical carboxylate linkers (e.g., BDC) are suitable for the construction of electrically conducting CPs, due to acceptedly higher covalency in metal-ligand bonding compared to the electrically insulating carboxylate CPs or metal-organic frameworks. At the same time, the direct comparison between insulating CPs 1 and 2 with CP 3 emphasizes that the electronic structure of the metal is likewise a crucial aspect to construct electrically conductive materials.

Exploiting click-chemistry: backbone post-functionalisation of homoleptic gold(I) 1,2,3-triazole-5-ylidene complexes.

The synthesis of a homoleptic azide-functionalised Au(I) bis-1,2,3-triazole-5-ylidene complex is reported, starting from a backbone-modified 1,2,3-triazolium salt ligand precursor. The incorporated azide handle allows for a straightforward modification of the complex according to click-chemistry protocols without impacting the steric shielding around the metal center, demonstrating the superiority of the presented triazole ligand framework over imidazole based systems. Employing the SPAAC and the CuAAC reactions, post-modification of the complex is facilitated with two model substrates, while retaining very high antiproliferative activity (nanomolar range IC50 values) in A2780 and MCF-7 human cancer cells.

Bright circularly polarized photoluminescence in chiral layered hybrid lead-halide perovskites.

Hybrid perovskite semiconductor materials are predicted to lock chirality into place and encode asymmetry into their electronic states, while softness of their crystal lattice accommodates lattice strain to maintain high crystal quality with low defect densities, necessary for high luminescence yields. We report photoluminescence quantum efficiencies as high as 39% and degrees of circularly polarized photoluminescence of up to 52%, at room temperature, in the chiral layered hybrid lead-halide perovskites (R/S/Rac)-3BrMBA2PbI4 [3BrMBA = 1-(3-bromphenyl)-ethylamine]. Using transient chiroptical spectroscopy, we explain the excellent photoluminescence yields from suppression of nonradiative loss channels and high rates of radiative recombination. We further find that photoexcitations show polarization lifetimes that exceed the time scales of radiative decays, which rationalize the high degrees of polarized luminescence. Our findings pave the way toward high-performance solution-processed photonic systems for chiroptical applications and chiral-spintronic logic at room temperature.

Exploring the Anticancer Activity of Tamoxifen-Based Metal Complexes Targeting Mitochondria.

Two new 'hybrid' metallodrugs of Au(III) (AuTAML) and Cu(II) (CuTAML) were designed featuring a tamoxifen-derived pharmacophore to ideally synergize the anticancer activity of both the metal center and the organic ligand. The compounds have antiproliferative effects against human MCF-7 and MDA-MB 231 breast cancer cells. Molecular dynamics studies suggest that the compounds retain the binding activity to estrogen receptor (ERα). In vitro and in silico studies showed that the Au(III) derivative is an inhibitor of the seleno-enzyme thioredoxin reductase, while the Cu(II) complex may act as an oxidant of different intracellular thiols. In breast cancer cells treated with the compounds, a redox imbalance characterized by a decrease in total thiols and increased reactive oxygen species production was detected. Despite their different reactivities and cytotoxic potencies, a great capacity of the metal complexes to induce mitochondrial damage was observed as shown by their effects on mitochondrial respiration, membrane potential, and morphology.

Silver and Gold Pillarplex Pseudorotaxanes from α,ω-Dicarboxylic Acids.

A series of pseudorotaxanes with supramolecular organometallic silver(I) and gold(I) pillarplexes acting as rings and different α,ω-dicarboxylic acids as axle components are reported. The successful formation of the host-guest complexes is shown by 1 H NMR spectroscopy and respective NMR titration. Additional evaluation with ITC titration experiments yielded dissociation constants (Kd ) ranging from 10-5 to 10-7  M. Single-crystal X-Ray diffraction analysis reveals a particularly exciting pore alignment of different examples in the solid state depending on the length of the guest. The work highlights, that dicarboxylic acids can penetrate the tight tubular pillarplex pore, paving the way to future mechanically interlocked molecules and materials.

Interplay between coordination sphere engineering and properties of nickel diketonate-diamine complexes as vapor phase precursors for the growth of NiO thin films.

NiO-based films and nanostructured materials have received increasing attention for a variety of technological applications. Among the possible strategies for their fabrication, atomic layer deposition (ALD) and chemical vapor deposition (CVD), featuring manifold advantages of technological interest, represent appealing molecule-to-material routes for which a rational precursor design is a critical step. In this context, the present study is focused on the coordination sphere engineering of three heteroleptic Ni(II) ß-diketonate-diamine adducts of general formula [NiL2TMEDA] [L = 1,1,1-trifluoro-2,4-pentanedionate (tfa), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionate (fod) or 2,2,6,6-tetramethyl-3,5-heptanedionate (thd), and TMEDA = N,N,N',N'-tetramethylethylenediamine]. Controlled variations in the diketonate structure are pursued to investigate the influence of steric hindrance and fluorination degree on the chemico-physical characteristics of the compounds. A multi-technique investigation supported by density functional calculations highlights that all complexes are air-insensitive and monomeric and that their thermal properties and fragmentation patterns are directly dependent on functional groups in the diketonate ligands. Preliminary thermal CVD experiments demonstrate the precursors' suitability for the obtainment of NiO films endowed with flat and homogeneous surfaces, paving the way to future implementation for CVD end-uses.

Organometallic Pillarplexes That Bind DNA 4-Way Holliday Junctions and Forks.

Holliday 4-way junctions are key to important biological DNA processes (insertion, recombination, and repair) and are dynamic structures that adopt either open or closed conformations, the open conformation being the biologically active form. Tetracationic metallo-supramolecular pillarplexes display aryl faces about a cylindrical core, an ideal structure to interact with open DNA junction cavities. Combining experimental studies and MD simulations, we show that an Au pillarplex can bind DNA 4-way (Holliday) junctions in their open form, a binding mode not accessed by synthetic agents before. Pillarplexes can bind 3-way junctions too, but their large size leads them to open up and expand that junction, disrupting the base pairing, which manifests in an increased hydrodynamic size and lower junction thermal stability. At high loading, they rearrange both 4-way and 3-way junctions into Y-shaped forks to increase the available junction-like binding sites. Isostructural Ag pillarplexes show similar DNA junction binding behavior but lower solution stability. This pillarplex binding contrasts with (but complements) that of metallo-supramolecular cylinders, which prefer 3-way junctions and can rearrange 4-way junctions into 3-way junction structures. The pillarplexes' ability to bind open 4-way junctions creates exciting possibilities to modulate and switch such structures in biology, as well as in synthetic nucleic acid nanostructures. In human cells, the pillarplexes do reach the nucleus, with antiproliferative activity at levels similar to those of cisplatin. The findings provide a new roadmap for targeting higher-order junction structures using a metallo-supramolecular approach, as well as expanding the toolbox available to design bioactive junction binders into organometallic chemistry.

A set of closely related methyltransferases for site-specific tailoring of anthraquinone pigments.

Modification of the polyketide anthraquinone AQ-256 in the entomopathogenic Photorhabdus luminescens involves several O-methylations, but the biosynthetic gene cluster antA-I lacks corresponding tailoring enzymes. We here describe the identification of five putative, highly homologous O-methyltransferases encoded in the genome of P. luminescens. Activity assays in vitro and deletion experiments in vivo revealed that three of them account for anthraquinone tailoring by producing three monomethylated and two dimethylated species of AQ-256. X-ray structures of all five enzymes indicate high structural and mechanistic similarity. As confirmed by structure-based mutagenesis, a conserved histidine at the active site likely functions as a general base for substrate deprotonation and subsequent methyl transfer in all enzymes. Eight complex structures with AQ-256 as well as mono- and dimethylated derivatives confirm the substrate specificity patterns found in vitro and visualize how single amino acid differences in the active-site pockets impact substrate orientation and govern site-specific methylation.

Alkaline Earth Metal-Organic Frameworks Based on Tetratopic Anthraquinone-Based Linkers: Synthesis, Characterization, and Photochemical Applications.

A tetratopic bis(diphenylamino)anthraquinone linker is presented, and its physicochemical properties are evaluated. The linker is shown to successfully coordinate alkaline earth metals leading to four new reported metal-organic frameworks (MOFs), which have been fully characterized, including single-crystal X-ray diffraction. The physicochemical and emissive properties of the MOF materials are investigated and compared to those of the uncoordinated ligand. Finally, the catalytic behavior of the ligand and the MOF materials toward the photooxidation of sulfides is described.

Highly-fluorescent BODIPY-functionalised metallacages as drug delivery systems: synthesis, characterisation and cellular accumulation studies.

With the aim of designing new metallosupramolecular architectures for drug delivery, research has focused on porous 3-dimensional (3D)-metallacages able to encapsulate cytotoxic agents protecting them from metabolism while targeting them to cancer sites. Here, two self-assembled [Pd2L4]4+ cages (CG1 and CG2) featuring 3,5-bis(3-ethynylpyridine)phenyl ligands (L) exo-functionalised with dipyrromethene (BODIPY) groups have been synthesised and characterised by different methods, including NMR spectroscopy and mass spectrometry. 1H NMR spectroscopy studies shows that the cages are able to encapsulate the anticancer drug cisplatin in their hydrophobic cavity, as evidenced by electrostatic potential (ESP) analysis based on XRD studies. The stability of the cages in an aqueous environment, and in the presence of the intracellular reducing agent glutathione, has been confirmed by UV-visible absorption spectroscopy. The luminescence properties of the cages enabled the investigation of their cellular uptake and intracellular localisation in human cancer cells by confocal laser scanning microscopy. In melanoma A375 cells, cage CG1 is taken up via active transport and endocytic trafficking studies show little evidence of transport through the early endosome while the cages accumulated in melanosomes rather than lysosomes. The antiproliferative activity of the lead cage was investigated in A375 together with two breast cancer cell lines, SK-BR-3 and MCF7. While the cage per se is non-cytotoxic, very different antiproliferative effects with respect to free cisplatin were evidenced for the [(cisplatin)2⊂CG1·BF4] complex in the various cell lines, which correlate with its different intracellular localisation profiles. The obtained preliminary results provide a new hypothesis on how the subcellular localisation of the cage affects the cisplatin intracellular release.

Multivariate Analysis Identifying [Cu(N

White light-emitting electrochemical cells (LECs) comprising only [Cu(N^N)(P^P)]+ have not been reported yet, as all the attempts toward blue-emitting complexes failed. Multivariate analysis, based on prior-art [Cu(N^N)(P^P)]+ -based thin-film lighting (>90 papers) and refined with computational calculations, identifies the best blue-emitting [Cu(N^N)(P^P)]+ design for LECs, that is, N^N: 2-(4-(tert-butyl)phenyl)-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine and P^P: 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, to achieve predicted thin-film emission at 490 nm and device performance of 3.8 cd A-1 @170 cd m-2 . Validation comes from synthesis, X-ray structure, thin-film spectroscopic/microscopy/electrochemical characterization, and device optimization, realizing the first [Cu(N^N)(P^P)]+ -based blue-LEC with 3.6 cd A-1 @180 cd m-2 . This represents a record performance compared to the state-of-the-art tricoordinate Cu(I)-complexes blue-LECs (0.17 cd A-1 @20 cd m-2 ). Versatility is confirmed with the synthesis of the analogous complex with 2-(4-(tert-butyl)phenyl)-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyrazine (N^N), showing a close prediction/experiment match: λ = 590/580 nm; efficiency = 0.55/0.60 cd A-1 @30 cd m-2 . Finally, experimental design is applied to fabricate the best white multicomponent host:guest LEC, reducing the number of trial-error attempts toward the first white all-[Cu(N^N)(P^P)]+ -LECs with 0.6 cd A-1 @30 cd m-2 . This corresponds to approximately ten-fold enhancement compared to previous LECs (<0.05 cd A-1 @<12 cd m-2 ). Hence, this work sets in the first multivariate approach to design emitters/active layers, accomplishing first-class [Cu(N^N)(P^P)]+ -based blue/white LECs that were previously elusive.

Introducing Benzene-1,3,5-tri(dithiocarboxylate) as a Multidentate Linker in Coordination Chemistry.

Benzene-1,3,5-tri(dithiocarboxylate) (BTDTC3-), the sulfur-donor analogue of trimesate (BTC3-, benzene-1,3,5-tricarboxylate), is introduced, and its potential as a multidentate, electronically bridging ligand in coordination chemistry is evaluated. For this, the sodium salt Na3BTDTC has been synthesized, characterized, and compared with the sodium salt of the related ditopic benzene-1,4-di(dithiocarboxylate) (Na2BDDTC). Single-crystal X-ray diffraction of the respective tetrahydrofuran (THF) solvates reveals that such multitopic aromatic dithiocarboxylate linkers can form both discrete metal complexes (Na3BTDTC·9THF) and (two-dimensional) coordination polymers (Na2BDDTC·4THF). Additionally, the versatile coordination behavior of the novel BTDTC3- ligand is demonstrated by successful synthesis and characterization of trinuclear Cu(I) and hexanuclear Mo(II)2 paddlewheel complexes. The electronic structure and molecular orbitals of both dithiocarboxylate ligands as well as their carboxylate counterparts are investigated by density functional theory computational methods. Electrochemical investigations suggest that BTDTC3- enables electronic communication between the coordinated metal ions, rendering it a promising tritopic linker for functional coordination polymers.

Investigation of Solvatomorphism and Its Photophysical Implications for Archetypal Trinuclear Au3(1-Methylimidazolate)3.

A new solvatomorph of [Au3(1-Methylimidazolate)3] (Au3(MeIm)3)-the simplest congener of imidazolate-based Au(I) cyclic trinuclear complexes (CTCs)-has been identified and structurally characterized. Single-crystal X-ray diffraction revealed a dichloromethane solvate exhibiting remarkably short intermolecular Au⋯Au distances (3.2190(7) Å). This goes along with a dimer formation in the solid state, which is not observed in a previously reported solvent-free crystal structure. Hirshfeld analysis, in combination with density functional theory (DFT) calculations, indicates that the dimerization is generally driven by attractive aurophilic interactions, which are commonly associated with the luminescence properties of CTCs. Since Au3(MeIm)3 has previously been reported to be emissive in the solid-state, we conducted a thorough photophysical study combined with phase analysis by means of powder X-ray diffraction (PXRD), to correctly attribute the photophysically active phase of the bulk material. Interestingly, all investigated powder samples accessed via different preparation methods can be assigned to the pristine solvent-free crystal structure, showing no aurophilic interactions. Finally, the observed strong thermochromism of the solid-state material was investigated by means of variable-temperature PXRD, ruling out a significant phase transition being responsible for the drastic change of the emission properties (hypsochromic shift from 710 nm to 510 nm) when lowering the temperature down to 77 K.

Facile preparation of a cobalt diamine diketonate adduct as a potential vapor phase precursor for Co3O4films.

Co3O4 thin films and nanosystems are implemented in a broad range of functional systems, including gas sensors, (photo)catalysts, and electrochemical devices for energy applications. In this regard, chemical vapor deposition (CVD) is a promising route for the fabrication of high-quality films in which the precursor choice plays a key role in the process development. In this work, a heteroleptic cobalt complex bearing fluorinated diketonate ligands along with a diamine moiety [Co(tfa)2·TMEDA; tfa = 1,1,1-trifluoro-2,4-pentanedionate and TMEDA = N,N,N',N'-tetramethylethylenediamine] is investigated as a potential Co molecular precursor for the CVD of Co3O4 systems. For the first time, the compound is characterized by crystal structure determination and comprehensive analytical studies, focusing also on its thermal properties and fragmentation patterns, important figures of merit for a CVD precursor. The outcomes of this investigation, accompanied by detailed theoretical studies, highlight its very favorable properties for CVD applications. In fact, growth experiments under oxygen atmospheres containing water vapor revealed the suitability of Co(tfa)2·TMEDA for the fabrication of high-quality, phase-pure Co3O4 thin films. The versatility of the proposed strategy in tailoring Co3O4 structural/morphological features highlights its potential to obtain multi-functional films with controllable properties for a variety of eventual technological end-uses.

C-C Cross-Couplings from a Cyclometalated Au(III) C ∧ N Complex: Mechanistic Insights and Synthetic Developments.

In recent years, the reactivity of gold complexes was shown to extend well beyond π-activation and to hold promises to achieve selective cross-couplings in several C-C and C-E (E=heteroatom) bond forming reactions. Here, with the aim of exploiting new organometallic species for cross-coupling reactions, we report on the Au(III)-mediated C(sp2 )-C(sp) occurring upon reaction of the cyclometalated complex [Au(CCH2 N)Cl2 ] (1, CCH2 N=2-benzylpyridine) with AgPhCC. The reaction progress has been monitored by NMR spectroscopy, demonstrating the involvement of a number of key intermediates, whose structures have been unambiguously ascertained through 1D and 2D NMR analyses (1 H, 13 C, 1 H-1 H COSY, 1 H-13 C HSQC and 1 H-13 C HMBC) as well as by HR-ESI-MS and X-ray diffraction studies. Furthermore, crystallographic studies have serendipitously resulted in the authentication of zwitterionic Au(I) complexes as side-products arising from cyclization of the coupling product in the coordination sphere of gold. The experimental work has been paralleled and complemented by DFT calculations of the reaction profiles, providing valuable insight into the structure and energetics of the key intermediates and transition states, as well as on the coordination sphere of gold along the whole process. Of note, the broader scope of the cross-coupling at the Au(III) CCH2 N centre has also been demonstrated studying the reaction of 1 with C(sp2 )-based nucleophiles, namely vinyl and heteroaryl tin and zinc reagents. These reactions stand as rare examples of C(sp2 )-C(sp2 ) cross-couplings at Au(III).

Preparation of Neutral trans - cis [Ru(O2CR)2P2(NN)], Cationic [Ru(O2CR)P2(NN)](O2CR) and Pincer [Ru(O2CR)(CNN)P2] (P = PPh3, P2 = diphosphine) Carboxylate Complexes and their Application in the Catalytic Carbonyl Compounds Reduction.

The diacetate complexes trans-[Ru(κ1-OAc)2(PPh3)2(NN)] (NN = ethylenediamine (en) (1), 2-(aminomethyl)pyridine (ampy) (2), 2-(aminomethyl)pyrimidine (ampyrim) (3)) have been isolated in 76-88% yield by reaction of [Ru(κ2-OAc)2(PPh3)2] with the corresponding nitrogen ligands. The ampy-type derivatives 2 and 3 undergo isomerization to the thermodynamically most stable cationic complexes [Ru(κ1-OAc)(PPh3)2(NN)]OAc (2a and 3a) and cis-[Ru(κ1-OAc)2(PPh3)2(NN)] (2b and 3b) in methanol at RT. The trans-[Ru(κ1-OAc)2(P2)2] (P2 = dppm (4), dppe (5)) compounds have been synthesized from [Ru(κ2-OAc)2(PPh3)2] by reaction with the suitable diphosphine in toluene at 95 °C. The complex cis-[Ru(κ1-OAc)2(dppm)(ampy)](6) has been obtained from [Ru(κ2-OAc)2(PPh3)2] and dppm in toluene at reflux and reaction with ampy. The derivatives trans-[Ru(κ1-OAc)2P2(NN)] (7-16; NN = en, ampy, ampyrim, 8-aminoquinoline; P2 = dppp, dppb, dppf, (R)-BINAP) can be easily synthesized from [Ru(κ2-OAc)2(PPh3)2] with a diphosphine and treatment with the NN ligands at RT. Alternatively these compounds have been prepared from trans-[Ru(OAc)2(PPh3)2(NN)] by reaction with the diphosphine in MEK at 50 °C. The use of (R)-BINAP affords trans-[Ru(κ1-OAc)2((R)-BINAP)(NN)] (NN = ampy (11), ampyrim (15)) isolated as single stereoisomers. Treatment of the ampy-type complexes 8-15 with methanol at RT leads to isomerization to the cationic derivatives [Ru(κ2-OAc)P2(NN)]OAc (8a-15a; NN = ampy, ampyrim; P2 = dppp, dppb, dppf, (R)-BINAP). Similarly to 2, the dipivalate trans-[Ru(κ1-OPiv)2(PPh3)2(ampy)] (18) is prepared from [Ru(κ2-OPiv)2(PPh3)2] (17) and ampy in CHCl3. The pincer acetate [Ru(κ1-OAc)(CNNOMe)(PPh3)2] (19) has been synthesized from [Ru(κ2-OAc)2(PPh3)2] and HCNNOMe ligand in 2-propanol with NEt3 at reflux. In addition, the dppb pincer complexes [Ru(κ1-OAc)(CNN)(dppb)] (CNN = AMTP (20), AMBQPh (21)) have been obtained from [Ru(κ2-OAc)2(PPh3)2], dppb, and HAMTP or HAMBQPh with NEt3, respectively. The acetate NN and pincer complexes are active in transfer hydrogenation with 2-propanol and hydrogenation with H2 of carbonyl compounds at S/C values of up to 10000 and with TOF values of up to 160000 h-1.

Molecular Oxygen Activation by Redox-Switchable Anthraquinone-Based Metal-Organic Frameworks.

A dipyridyl-substituted anthraquinone (2,6-di(pyridin-4-yl)-9,10-anthraquinone, DPAq) was incorporated as a redox-active linker molecule into crystalline coordination networks. The oxidation state of the organic linker can be selectively controlled prior to framework formation and furthermore be maintained in the solid state. Hydrogen bonding is identified to be a substantial stabilization factor. Additionally, it is shown that the anthraquinone-anthrahydroquinone redox pair can be switched reversibly even after incorporation in the solid state by a thermal treatment/soaking procedure-going along with the formation of hydrogen peroxide from molecular oxygen (air) during the oxidation process.