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Abstract New composite materials containing metal-organic framework (MOF-5) particles were manufactured by 3D printing. The optimal composition of the photopolymer formulation and printing conditions ensuring the highest quality of printing were selected. Retention of the metal-organic framework (MOF) structure in the resulting composite objects was demonstrated by powder X-ray diffraction. The distribution of MOF-5 particles over the whole bulk of the 3D product was studied by X-ray computed tomography. In the future, composite materials of this type containing catalytically active MOFs, with their structure and properties being controllable at the micro and macro levels, could find application as catalysts of various chemical processes.

A series of new bis(pyrazol-3-yl)pyridines (LR) N,N′-disubstituted by 4-functionalized 2,6-dibromophenyl groups have been synthesized to study the effect of a distal substituent on the spin-crossover (SCO) behaviour of the iron(II) complexes [Fe(LR)2](ClO4)2 by variable-temperature magnetometry, NMR spectroscopy, and X-ray diffraction. The SCO-assisting tendency of the substituents with different electronic and steric properties (i.e., the bromine atom and the methyl group) in the para-position of the 2,6-dibromophenyl group is discussed. Together with earlier reported SCO-active iron(II) complexes with N,N′-disubstituted bis(pyrazol-3-yl)pyridines, these new complexes open the way for this family of SCO compounds to emerge as an effective ‘tool’ in revealing structure–function relations, a prerequisite for successful molecular design of switchable materials for future breakthrough applications in sensing, switching, and memory devices.

1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene, 1, was tested as a reagent for the reductive silylation of various unsaturated functionalities, including N-heterocycles, quinones, and other redox-active moieties in addition to deoxygenation of main group oxides. Whereas most reactions tested are thermodynamically favorable, based on DFT calculations, a few do not occur, perhaps giving limited insight on the mechanism of this very attractive reductive process. Of note, reductive silylation reactions show a strong solvent dependence where a polar solvent facilitates conversions.

Metal-ligand complexation at surfaces utilizing redox-active ligands has been demonstrated to produce uniform single-site metals centers in regular coordination networks. Two key design considerations are the electron storage capacity of the ligand and the metal-coordinating pockets on the ligand. In an effort to move toward greater complexity in the systems, particularly dinuclear metal centers, we designed and synthesized tetraethyltetra-aza-anthraquinone, TAAQ, which has superior electron storage capabilities and four ligating pockets in a diverging geometry. Cyclic voltammetry studies of the free ligand demonstrate its ability to undergo up to a four-electron reduction. Solution-based studies with an analogous ligand, diethyldi-aza-anthraquinone, demonstrate these redox capabilities in a molecular environment. Surface studies conducted on the Au(111) surface demonstrate TAAQ's ability to complex with Fe. This complexation can be observed at different stoichiometric ratios of Fe:TAAQ as Fe 2p core level shifts in X-ray photoelectron spectroscopy. Scanning tunneling microscopy experiments confirmed the formation of metal-organic coordination structures. The striking feature of these structures is their irregularity, which indicates the presence of multiple local binding motifs. Density functional theory calculations confirm several energetically accessible Fe:TAAQ isomers, which accounts for the non-uniformity of the chains.

We prepared a series of thermally remendable and recyclable polyurethanes crosslinked via reversible furan-maleimide Diels–Alder reaction based on TDI end-caped branched Voranol 3138 terminated with difurfurylamine and 4,4′-bis(maleimido)diphenylmethane (BMI). We showed that Young modulus strongly depends on BMI content (from 8 to 250 MPa) that allows us to obtain materials of different elasticity as simple as varying BMI content. The ability of DA and retro-DA reactions between furan and maleimide to reversibly bind material components was investigated by NMR spectroscopy, differential scanning calorimetry, and recycle testing. All polymers obtained demonstrated high strengths and could be recovering without significant loss in mechanical properties for at least five reprocessing cycles.

Metal-organic coordination networks at surfaces, formed by on-surface redox assembly, are of interest for designing specific and selective chemical function at surfaces for heterogeneous catalysts and other applications. The chemical reactivity of single-site transition metals in on-surface coordination networks, which is essential to these applications, has not previously been fully characterized. Here, we demonstrate with a surface-supported, single-site V system that not only are these sites active toward dioxygen activation, but the products of that reaction show much higher selectivity than traditional vanadium nanoparticles, leading to only one V-oxo product. We have studied the chemical reactivity of one-dimensional metal-organic vanadium - 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPTZ) chains with O2. The electron-rich chains self-assemble through an on-surface redox process on the Au(100) surface and are characterized by X-ray photoelectron spectroscopy, scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, and density functional theory. Reaction of V-DPTZ chains with O2 causes an increase in V oxidation state from VII to VIV, resulting in a single strongly bonded (DPTZ2-)VIVO product and spillover of O to the Au surface. DFT calculations confirm these products and also suggest new candidate intermediate states, providing mechanistic insight into this on-surface reaction. In contrast, the oxidation of ligand-free V is less complete and results in multiple oxygen-bound products. This demonstrates the high chemical selectivity of single-site metal centers in metal-ligand complexes at surfaces compared to metal nanoislands.

A review of the works devoted to the synthesis and investigation of the properties of block copolymers containing fragments of polytetrahydrofuran obtained from renewable natural raw materials is presented. It is shown that the presence of chemically bonded blocks of elastic polytetrahydrofuran in rigid-chain polymer matrices increases their impact resistance and elongation at break, reduces the viscosity of the melt, and improves miscibility with other polymers. It is expected that a similar positive effect of polytetrahydrofuran elastic blocks will be observed in polymer composites filled with dispersed and continuous fibers.

In this work, L-lactide, acting as a cyclic AB monomer, was copolymerized with various AB2 comonomers. Depending on the nature of the AB2 comonomer, it was either a combination of L-lactide ring-opening polymerization with glycidol polymerization or a combination of L-lactide ring-opening polymerization with 2,2-bis (hydroxymethyl) propionic acid (BHP) polycondensation. Both synthetic methods resulted in branched copolyesters. A number of polymers with varying degrees of branching were obtained by systematically changing the proportion of comonomer AB2. The polymers were characterized using 1H NMR spectroscopy and SEC, and their thermal properties were studied using differential scanning calorimetry and thermogravimetric analysis. Also were investigated the viscosity of the solution and the wettability of the branched copolymers. Although structurally similar macromolecules were formed in both synthesis methods, polymers with BHP as AB2 comonomers have higher melting- and glass transition temperatures, higher thermal stability, solution viscosity and lower wettability than polymers with glycidol as AB2 comonomers.

Thermally-remendable and recyclable polyurethane was obtained via Diels-Alder reaction using branched glycol Voranol 3138 (glycerin-derived block-copolymer of polyethylene and polypropylene) as soft segment and toluene-2,4-diisocyanate (TDI) as hard segment subsequently functionalized by terminal difurfurylamine groups. By cross-linking via Diels-Alder reaction with N,N’-bismaleimido-4,4′-diphenylmethane (BMI) new self-healing branched polyurethane was obtained. Polymer structure was characterized by NMR and IR spectroscopy along with thermal analysis methods (DSC and TGA). Resulting material has good processability and opportunity for recycling.

The process of removal of H+ and of Cl-, dehydrohalogenation, from (H₂L)FeCl₂ is investigated systematically, to understand the reactivity of the implied transient LFe(II). Reaction of (H₂L)FeCl₂ with 2 equivalents of LiN(SiMe₃)₂ yields LiClFe₂L₂, as its dimer with every iron 5-coordinate in an FeN₄Cl environment. To avoid Li+ cation derived from base, reaction of Na₂L with FeCl₂ gives a product Na₂[NaFe(HL)(L)]₂(LFeO) from addition of water, which reveals Na/pyrazolate Nβ interactions and a five coordinate oxo group in the OFe₃Na₂ core. Dehydrohalogenation in the presence of Ph₂PC₂H₄PPh₂ gives diamagnetic [LFe(κ²-dppe)]₂(μ-dppe) and LFe(κ²-dppe)(κ¹-dppe). Dehydrohalogenation in the presence of tBuNC gives diamagnetic LFe(CNtBu)₃. This is selectively methylated at both pyrazolate β-N to give LMeFe(tBuNC)₃²+ which is reduced with KC₈ to diamagnetic LMeFe(tBuNC)². Structure determination of these and IR data on isonitrile bands, show L²- to be a stronger donor than LMe. First installing triflate (to avoid the more persistent Cl-) facilitates access to LFe(Lewis base)₃²+ complexes, but this cation shows relatively weak binding of CO to LFeII, which implicates weak π basicity of that d6 species. Production of bis-pincer complexes (H₂L)₂Fe²+ and (LMe)₂Fe²+ in the presence of abundant Lewis base in polar medium is demonstrated, which illustrates a pincer ligand redistribution challenge to be kept in mind when trying to maintain a 1:1 Fe:pincer ratio, for highest reactivity.

A pyridyl pincer ligand was developed to incorporate steric bulk, through a PtBu2 arm, and proton responsivity, through a pyrazole pincer ligand arm, together with reactivity at benzylic hydrogen and redox activity within a 1,4 diazabutadiene moiety. Binding it to CoCl2 yielded square-pyramidal [(PNNH)CoCl2 ], which was deprotonated by Li[N(SiMe3 )2 ] to form [{Li(THF)2 PNN}CoCl2 ]. Reduction of this LiCl adduct with KC8 under CO atmosphere led to formation of CoI mono- and dicarbonyl complexes, which can be protonated but also further deprotonated at the benzylic CH group to give a dearomatized pyridyl group. The ligand was characterized in its neutral, monoanionic, and dianionic forms, and the anions were shown to exist as intimate ion pairs with Li+ bound to pyrazolate N and chloride bound to Lewis acidic cobalt. X-ray photoelectron spectroscopy was used to assay both Li content and cobalt oxidation states. The general character of binding of LiCl to a metal complex acidic at metal and nucleophilic at ligand (pyrazolate Nβ) is discussed, as are potential catalytic applications of the concept.

Tetrazines react with OCP-1 through a reverse electron demand Diels-Alder process to produce 3,6-disubstituted-1,2,4-diazaphosphinin-5-olates. DFT calculations reveal that both Diels-Alder and subsequent aromatization barriers are low for both EWG and ED tetrazine substituents. The structure of the solid sodium salt shows the interaction of Na+ with aryloxide and also both nitrogens of a neighboring anion, leading to coordination polymer character. 1,2,4-Diazaphosphinin-5-olates react as nucleophiles towards MeI and R3SiCl, respectively, and were installed on the (Ph3P)2Ru(CO)H fragment to investigate their properties as ligands.

Reaction of the unsymmetrically-armed pincer PNNH (phosphine, pyridyl, pyrazole) with FeCl2 yields a five coordinate monomer (PNNH)FeCl2, whose NH proton hydrogen bonds to capture THF. Deprotonation of this NH functionality with Li[N(SiMe3)2] does not give four coordinate (PNN)FeCl, but instead retains LiCl to yield (PNNLi)FeCl2, where Li bridges between the pyrazolate beta nitrogen and one chloride on Fe. One electron reduction of this compound under CO occurs with loss of LiCl to form square pyramidal monovalent iron in (PNN)Fe(CO)2, which is characterized by IR, Mossbauer, X-ray diffraction, EPR measurements and DFT calculations. Cyclic voltammetry of (PNN)Fe(CO)2 showed a reversible reduction wave and the reduction product was synthesized using KC8. The product (KPNN)Fe(CO)2 contains saturated, five coordinate Fe(0); the (PNN)Fe subunit is anionic, and the K+ cations cluster near the pyrazolate side of the two CO ligands, leaving the back side of potassium electrophile open to aggregate with the oxygen of CO of a neighboring unit, creating a polymeric chain. Reaction of (PNN)Fe(CO)2 with HBpin results in reduction of the metal center (by release of H2) and borylation of the pyrazole β-nitrogen. This redox active addition of the H-B bond across metal/ligand assembly is an unusual example of metal-ligand cooperativity and establishes a ligand which supports iron in three different oxidation states.

Various modifications of epoxy resins with maleimides and polyimide fragments results in the formation of heat-resistant materials with excellent mechanical and electrical properties together with high chemical, corrosion, and radiation resistance. Such materials can be used in the aerospace industry, electronics, instrument making, and other industries. The ability of some epoxy-maleimide resins to react with furanic groups through thermo-reversible Diels-Alder reaction open a new area in composite material science - self-healing binders. Selfhealing materials can restore their structure and mechanical properties after a damage that results in an increase of the service life several times and, therefore, reduce their cost. In this paper, maleimides were modified by diglycidyl ethers to obtain not previously described polyethers, capable of self-healing of mechanical properties after damage. All compounds were characterized by 1H NMR.

A triethyleneglycol-modified epoxy composition based on diglycidylfurfurylamine (FuEp) and 1,1’- (methylene-di-4,1-phenylene)bismaleimide (BMI) was cured with methyl hexahydrophthalic anhydride (MHPPA). The components of the composition can reversely binds through Diels-Alder reaction between furan and maleimide moieties. We studied the effect of TEG additive on the rheological and thermophysical properties of the binder, as well as the ability through thermal treatment. All compounds were characterized with NMR and IR spectroscopy. It was shown that TEG significantly reduces the curing time and the glass transition temperature of the cured samples, which allows to speed up the process of self-healing.

Prepolymer synthesized from toluene-2,4-diisocyanate (TDI) (hard segment), and polypropylene glycol (PPG-2000) (soft segment) was end-capped with difurfurylamine groups. A new cross-linked self-healing polyurethane was obtained via Diels-Alder reaction of the en-capped prepolymer with N,N’-bismaleimido-4,4’-diphenylmethane (BMI). Thermal reversibility of the Diels-Alder reaction (DA-reaction) between terminal furanic rings of the polyurethane prepolymer and bismaleimide cross-linking agent designed to be responsible for self-healing. Polymers were characterized by NMR and IR spectroscopy and thermal analysis (DSC and TGA). Thermal reversibility of the DA-bonds in the cross-linked polymer was confirmed by DSC. The synthesized polymer has good processability and potential recyclability.

A series of a new diglycidyl derivatives of aromatic amines containing a furan fragment was obtained. The synthetic scheme consists of two stages: reductive amination and epoxidation. We used industrially produced inexpensive amines and furfural as starting material. Diepoxides obtained are key components for development of epoxy binders capable of intrinsic self-healing based on the reversible Diels-Alder reaction between furan and maleimide. To demonstrate the possibility of self-healing, the Diels-Alder reaction adduct of one of the products with N-phenyl maleimide was isolated and characterized by 2D NMR spectroscopy. The reversibility of the reaction was confirmed by DSC experiment.

New reactive diluents based on bio-renewable raw materials are widely explored as additives to traditional resins. We investigated the effect of furfurylglycidyl ether on the rheological and thermomechanical properties of a widely used epoxy binder with an anhydride hardener. It was shown that the addition of 5-15% active diluent significantly reduces the viscosity of the composition to the values optimal for RTM and vacuum infusion technologies for fiber-reinforced plastics and does not lead to a significant decrease in heat resistance and Young’s modulus of the cured binder