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A new synthetic pathway is devised to selectively produce previously elusive heteroleptic iron(II) complexes of terpyridine and

A synthetic method for the new chain extenders with different amounts of furan groups and a prepolymer derived from three-furyl diol was developed. A series of polyurethanes cross-linked via the Diels-Alder reaction with various amounts of bismaleimide were produced. The structure, mechanical and thermal properties, and recycling ability of the obtained materials were investigated.

We present here a small series of compounds designed to modify the polymer chain of various polyurethanes in order to introduce a structural fragment with the ability of thermally-triggered reversible covalent interactions. Bismaleimides (2a-2e) were synthesized from commercially available aromatic and aliphatic symmetric diamines (1a-1e) and were further introduced into the Diels-Alder reaction with furfuryl alcohol as dienophiles. The Diels-Alder adducts (3a-3e) were obtained as a mixture of endo- and exo-isomer. The presence of symmetrical hydroxyl groups in the structure of the obtained compounds makes them suitable as chain extenders of low molecular weight diisocyanate prepolymers. The presence of a thermally reversible Diels-Alder reaction adduct in the structure of potential chain-extenders opens a possibility to create unique materials with self-healing properties. All compounds obtained were characterized by 1H, 13C NMR, ESI-HRMS, and IR spectroscopy. The thermochemical parameters of the reverse Diels-Alder reaction were established using DSC analysis.

The reaction of new 2,6-bis(pyrazol-3-yl)pyridine ligand (L) containing a redox-active ferrocenyl substituent with cobalt(II) salt gave the cobalt(II) complex [Co(L)2](ClO4)2 (I), which was isolated in a pure state and characterized by elemental analysis, NMR spectroscopy, cyclic voltammetry, and X-ray diffraction. According to X-ray diffraction data (CIF file CCDC no. 2049714) and the Evans method, which allows determining the spin state of paramagnetic compounds in solution on the basis of NMR spectra, the cobalt(II) ion in complex I occurs in the high-spin state and does not undergo temperature-induced spin transition in the temperature range of 120–370 K.

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.

This work presents a solution to one of the most fundamentally and practically important challenges in the production of silica-based aerogels, time consumption and expensiveness of these processes...

The design of new redox-switchable molecules requires the development of simple and efficient synthetic approaches. This study demonstrates the possibility of ortho-lithiation of ferrocenecarboxaldehyde (aryl)imines (Ia–Ic) followed by the reaction with ketones to give 1,2-disubstituted ferrocenes (IIa–IIc). These products, in turn, can be cyclized by treatment with trimethylsilyl triflate to give the cationic precursors of ferrocene-containing N-heterocyclic carbenes (IIIa–IIIc), in which the heterocycle is annulated to one of the ferrocene cyclopentadienyl ring. Treatment of IIIa–IIIc with a base in the presence of a source of rhodium afforded rhodium carbene complexes (IVa, IVb) in which the carbene ligand resembled cyclic alkylaminocarbenes in the electron-donor properties. Compounds Ib and IVa were studied by X-ray diffraction (CIF file CCDC nos. 2000413 and 2000414, respectively).

A series of industrial chitosans were analyzed on the presence of residual heavy metals. For the first time, optical microscopy data showed that chitosan solution retained a huge number of insoluble microparticles while transmittance electron microscopy revealed that insoluble fibrous microparticles were incrusted by crystalline nanoparticles with the sizes 5–50 nm. A series of filters used for chitosan solution filtration was analyzed on the presence of retained heavy metal and other residuals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDXS) and mass-spectrometry with inductively coupled plasma (ICP-MS) methods. The SEM-EDXS analysis revealed the presence of Fe residuals together with Si, Al, N and S in the particles found on the filters. ICP-MS analysis found the presence of heavy metals (mainly Fe, Cr and Ni) both on the filter surfaces and in the effluent chitosan solution passed though the filters. This study draws attention to the necessity of a careful selection of industrially manufactured chitosan in order to avoid hidden undesirable effects of chitosan on pharmaceuticals and biomaterials and gives a warning of inapplicability of a stainless-steel made apparatus as a reactor susceptible to caustic soda corrosion for chitin deacetylation and production of medical and food grade chitosan.

The reaction of a new tridentate ligand 2,6-bis(5-tert-butyl-1-(2,6-difluorophenyl)-1H-pyrazol-3-yl)pyridine (L) with the divalent iron salt affords the iron(II) complex [Fe(L)2](BF4)2 (I), which is isolated in the individual state and characterized by elemental analysis, NMR spectroscopy, and X-ray diffraction analysis. According to the X-ray diffraction results and data of the Evans method, which makes it possible to determine the spin state of paramagnetic compounds in a solution from the NMR spectra, the iron(II) ion in complex I exists in the high-spin state (S = 2 for Fe(II)) and undergoes no temperature-induced spin transition in a range of 120–345 K.

A new binuclear iron(III) oxo complex [(L)FeOFe(L)](PO2F2)4 (1) with PO2F2– counterions resulted from the oxidation of the hexafluorophosphate anion has been prepared by oxidation of an iron(II) complex with the tridentate ligand 2,6-bis(5-(4-fluorophenyl)-1H-pyrazol-3-yl)pyridine (L). According to X-ray diffraction studies, the iron(III) ions adopt the high-spin state, as in the previously described iron(III) oxo complex with tert-butyl substituted bis(pyrazol-3-yl)pyridine. At the same time, the presence of aromatic para-fluorophenyl substituents and $${\text{P}}{{{\text{O}}}_{2}}{\text{F}}_{2}^{ - }$$ counterions in oxo complex 1 decreases the twisting of bis(pyrazol-3-yl)pyridine ligands relative to each other, thus ensuring a less distorted molecular geometry of this complex.

The reactions of 2,6-bis(1,4-diphenyl-5-hydroxy-1H-pyrazol-3-yl)pyridine (L), which is the first representative of a series of 2,6-bis(pyrazol-3-yl)pyridine ligands bearing substituents in positions 1 and 4 of the pyrazol-3-yl ring, with the divalent iron and cobalt salts afford new Со(II) and Fe(II) complexes: [Co(L)2](ClO4)2 (I) and [Fe(L)2](ClO4)2 (II). The compounds are isolated in the individual state and characterized by elemental analysis, NMR spectroscopy, and X-ray diffraction analysis (CIF files CCDC nos. 1967892 (I) and 1967893 (II)). According to the data obtained, the transition metal ion in complexes I and II exists in the high-spin state (S = 3/2 for Co(II) and S = 2 for Fe(II)) in a range of 120–345 K, and the proposed modification of the ligand does not lead to the temperature-induced spin transition in both the solution and crystalline state.

The molecular design of spin-crossover complexes relies on controlling the spin state of a transition metal ion by proper chemical modifications of the ligands. Herein, the first N,N'-disubstituted 2,6-bis(pyrazol-3-yl)pyridines (3-bpp) are reported that, against the common wisdom, induce a spin-crossover in otherwise high-spin iron(II) complexes by increasing the steric demand of a bulky substituent, an ortho-functionalized phenyl group. As N,N'-disubstituted 3-bpp complexes have no pendant NH groups that make their spin state extremely sensitive to the environment, the proposed ligand design, which may be applicable to isomeric 1-bpp or other families of popular bi-, tri- and higher denticity ligands, opens the way for their molecular design as spin-crossover compounds for future breakthrough applications.

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.

The cobalt(II) and iron(II) complexes with 2,6-di(5-amino-1H-pyrazol-3-yl)pyridine (L), CoL2(ClO4)2 (I) and FeL2(ClO4)2 (II), are synthesized by the template reaction, isolated in the individual form, and characterized by elemental analysis, NMR spectroscopy, and thermogravimetry. The structures of complexes I and II (including the iron(II) complex obtained as two new solvate forms (FeL2(ClO4)2 ∙ 2(C2H5)2O ∙ H3CN (IIa) and FeL2(ClO4)2 ∙ (C2H5)2O ∙ CH3CN ∙ 0.75H2O (IIb)) are confirmed by X-ray diffraction analysis. The data obtained in the crystal (by the X-ray diffraction method) and in solutions (using the proposed approach to an analysis of paramagnetic shifts in 1H NMR spectra) indicate that the metal ion in the complexes exists in the high-spin state (S = 3/2 for Co(II) and S = 2 for Fe(II)) and undergoes no temperature-induced spin transition in a range of 120–300 K.

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.

The octahedral, S = 2, bis -pyrazolatopyridyl complex LFe(DMAP) 3 reacts with CO 2 in CH 3 CN to yield (LH)Fe(DMAP) 2 (O 3 C)Fe 2 (L)(HL), which is the product of capture of one CO 2 by one doubly deprotonated water molecule, then binding of one iron to each carbonate oxygen. In order to eliminate DMAP as a participant, [LiClFe 2 L 2 ] is shown to add one water per Fe 2 unit to give [LiClFe 2 (HL)(L)(OH)], with the Fe 2 L 2 unit capturing hydroxide, and this entire formula unit is linked into a dimer by Li/OH interactions, supplemented by hydrogen bonds to OH from nucleophilic pyrazolate nitrogens. This is suggested to be the process where carbonate is formed, promoted by the ability of the LFe unit to increase the nucleophilicity of H 2 O, and then attack CO 2 . Related to that conversion, we establish the structure of the conjugate base [Fe 2 L 2 (O)] 2- . Collectively, this shows the combined action of multiple Fe(II) reactants, together with pyrazolate nucleophile and Bronsted base in the hydration of CO 2 , the conversion effected by carbonic anhydrase.

The direct template reactions afford the cobalt(II) complexes (I–III) with the hydroxy- and acetyl-substituted 2,6-bis(pyrazol-3-yl)pyridine ligands containing the phenyl and 4-tert-butylphenyl group in position 1. All compounds are isolated in the individual state and characterized by elemental analysis and NMR spectroscopy. The X-ray diffraction data obtained for crystals of compound I (СIF file CCDC 1577238) and the data for solutions (using the proposed approach to analysis of paramagnetic NMR shifts on the basis of quantum chemical calculations) show that in the complexes the metal ion exists in the high-spin state (S = 3/2) and undergoes no temperature-induced spin transition in a temperature range of 120–300 K.

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.

The synthesis of bis(N1-phenyl-5-hydroxypyrazol-3-yl)pyridines ("L") is described, and these are silylated to achieve analogues ("Si2L") without the variable of the hydroxyl proton mobility. One hydroxyl example is characterized in its bis-pincer iron(II) complex, which shows every OH proton involved in hydrogen bonding. The steric bulk of the silylated N-phenyl-substituted ligands allows the synthesis and characterization of paramagnetic (Si2L)FeCl2 complexes, and one of these is reduced, under CO, to give the diamagnetic (Si2L)Fe(CO)2 species. Structural comparison and density functional theory calculations of the dichloride and dicarbonyl species show that much, but not all, of the reduction occurs at both the ligand pyridine and pyrazole rings, and thus this ligand type is more resistant to reduction than the simpler bis(iminopyridines). The OSiR3 substituent offers a useful diagnostic of reduction at pyrazole via the degree of π-donation to pyrazole by the oxygen lone pairs, and the stereoelectronic features of the NPh moiety are analyzed. The X-ray photoelectron spectroscopy binding energies of both iron and nitrogen are analyzed to show details of the locus of reduction.

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.

Here we report a combined use of THz-EPR and NMR spectroscopy for obtaining a detailed electronic structure of a long-known high-spin complex, cobalt(II) bis[tris(pyrazolyl)borate]. The lowest inter-Kramers transition was directly measured by THz-EPR spectroscopy, while the energies of higher Kramers doublets were estimated by a recently proposed NMR-based approach. Together, they produced magnetic parameters for a full model that explicitly includes spin–orbit coupling. This approach is applicable to all transition metal ions for which the spin–orbit coupling cannot be treated perturbatively.

Reaction of 3,6-disubstituted-1,2,4,5-tetrazines with water and PEt3 forms the corresponding 1,4-dihydrotetrazine and OPEt3. Thus PEt3, as a stoichiometric reductant, reduces water, and the resulting two reducing equivalents serve to doubly hydrogenate the tetrazine. A variety of possible initial interactions between electron-deficient tetrazine and electron-rich PR3, including a charge transfer complex, were evaluated by density functional calculations which revealed that the energy of all these make them spectroscopically undetectable at equilibrium, but one of these is nevertheless suggested as the intermediate in the observed redox reaction. The relationship of this to the Mitsunobu reaction, which absorbs the components of water evolved in the conversion of alcohol and carboxylic acid to ester, with desirable inversion at the alcohol carbon, is discussed. This enables a modified Mitsunobu reaction, with tetrazine replacing EtO2CN=NCO2Et (DEAD), which has the advantage that dihydrotetrazine can be recycled to tetrazine by oxidation with O2, something impossible with the hydrogenated DEAD. For this tetrazine version, a betaine-like intermediate is undetectable, but its protonated form is characterized, including by X-ray structure and NMR spectroscopy.

We have studied the reactions of furfural-acetone resins and their main components, i.e., monoand difurfurylidene acetones, with aliphatic polyamines and organic acid anhydrides. It is shown that furfural-acetone resins can be hardened under the action of polyamines and do not react with acid anhydrides. probable mechanism of the reaction with polyamines is proposed.

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.

Rational, systematic tuning of single-site metal centers on surfaces offers a new approach to increase selectivity in heterogeneous catalysis reactions. Although such metal centers of uniform oxidation states have been achieved, the ability to control their oxidation states through the use of carefully designed ligands had not been shown. To this end, tetrazine ligands functionalized by two pyridinyl or pyrimidinyl substituents were deposited, along with vanadium metal, on the Au(100) surface. The greater oxidizing power of the bis-pyrimidinyltetrazine facilitates the on-surface redox formation of V(3+), compared to V(2+) when paired with the bis-pyridinyltetrazine, as determined by X-ray photoelectron spectroscopy. This demonstrates the ability to control metal oxidation states in surface coordination architectures by altering the redox properties of organic ligands. The metal-ligand complexes take the form of one-dimensional polymeric chains, resolved by scanning tunneling microscopy. The chain structures in the first layer are very uniform and are based on the same quasi-square-planar coordination geometry around single-site V with either ligand. Formation of a different, dimer structure is observed in the early stages of the second layer formation. These systems offer new opportunities in controlling the oxidation state of single-site transition metal atoms at a surface for new advances in heterogeneous catalysts.

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

Pincer complexes are widely used in catalysis and activation of small molecules. We present here the synthesis and spectroscopic study of rhodium dihydrogen and dinitrogen complexes with metallocene-based P,C,P pincer ligands. Relative electron donor ability of ferrocene-, ruthenocene- and benzene-derived pincer ligands, as well as H H distance were elucidated based on JHD coupling constants and T1 relaxation time for dihydrogen complexes.

A series of N-aryl ferrocenylmethanimines was successfully lithiated at ortho-position with the following treatment with various electrophiles such as ketone, alkyl and silyl halides yielding 1,2-disubstituted ferrocenes with good yields. The product of benzophenone addition was characterized with X-ray diffraction study. We showed that cyclization of 2-hydroxymethylferrocenylcarbimines with Tf2O led to formation of 5H-pyrrolo[3,4-a]ferrocen-6-ium salt - a potential precursor of ferrocene-based heterocyclic carbenes.

The rheological properties of an epoxy-furan composite incorporating the new low-viscosity furan resin LE828 were studied in the temperature range between 25 and 70°C. Furfural-acetone resin is shown to be an effective and active diluent for epoxy-diane (epoxybisphenol A) resin.

The alkylation of imidazole and 5-benzyloxycarbonyl-3,4-diethylpyrrole with 1,3-bis-(hydroxymethyl)ferrocene (1) afforded bis-imidazole (4) and bis-pyrrole (7) derivatives of ferrocene, respectively. The reaction of diol 1 with trifluoroacetic acid gave the dicarbocationic complex [{1,3-(CH2)2C5H3}Fe(C5H5)]2+ (2) characterized by 1H NMR spectroscopy.

Cationic ruthenium hydrido-carbonyls {RuH(CO)[tBuP,CH,PM]}BArF4 (M = Fe, 3; M = Ru, 4) (ArF = 3,5-(CF3)2C6H3) obtained in the reaction of H2 with RuCl(CO)[tBuP,C,PM] (M = Fe, 1; M = Ru, 2) in the presence of NaBArF4 add CO smoothly, giving the corresponding dicarbonyl complexes {RuH(CO)2[tBuP,CH,PM]}BArF4 (M = Fe, 11; M = Ru, 12). According to X-ray analysis of 11 and 12, addition of extra CO to complexes 3 and 4 leads to strengthening of the C(1)−H(1)···Ru(1) agostic interaction. Simultaneously, CO addition to 3 and 4 triggers a sequence (up to three steps) of unprecedented intramolecular rearrangements including migration of H atoms. First metallocenylidene complexes {Ru(CO)2[tBuP,C,PM]}BArF4 (M = Fe, 15; M = Ru, 16) were obtained in the course of these rearrangements accompanied by H2 evolution.

Rhodium hydrido chloride pincer complex RhH(Cl)[2,6-(Buptb2PO)b2Cb6Hb3] was synthesized and used for the preparation of new complexes with labile two-electron ligands Rh(L)[2,6-(Buptb2PO)b2Cb6Hb3] (L = MeCN or S(CHb2)b4) and complexes with small molecules, such as CO, Ob2, Hb2, and Nb2.