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Manganese catalysis has attracted significant attention in the last few years. In comparison with the extensively studied Mn complexes bearing phosphine‐based pincer ligands, catalysis with Mn containing N‐heterocyclic carbenes (NHC) is poorly developed. In this work, new manganese(I) complexes bearing an NHC ligand with picolyl wingtip substituents (an N,C,N ligand) have been synthesized and fully characterized. The structure of fac‐[Mn(CO)3(κ2N,C,N)Br] and fac‐[Mn(CO)3(κ3N,C,N)](OTf) complexes with a bidentate and tridentate coordination of the N,C,N ligand, respectively, has been elucidated by single crystal X‐ray diffraction studies. These Mn complexes were applied as catalysts for the visible light‐induced hydrosilylation of ketones. The mild protocol operated efficiently at room temperature under visible light irradiation (blue LED), enabling the conversion of a wide variety of aromatic ketones to their respective alcohols in high yields. Evidence for radical intermediates and the participation of Mn‐H species has been demonstrated by a series of trapping experiments. [ABSTRACT FROM AUTHOR]

Invasive fungal diseases affect more than two million people worldwide. The increasing incidence of invasive fungal infections is the result of many factors, including an increase in the resistance to current drugs. As such, there is an urgent need to obtain new drugs that are efficient, selective, and able to overcome existing resistance mechanisms. Candida yeasts are responsible for more than 70% of all nosocomial invasive fungal diseases. In this work, we describe the synthesis of nickel (II)(NHC) complexes based on xanthines, by direct metalation of xanthinium salts with nickelocene NiCp2to yield [NiCpI(NHC)] complexes. For methyl caffeine, a biscarbene complex [NiCp(NHC)2]+is also formed, resulting from carbene dissociation from the corresponding monocarbene. [NiCpI(NHC)] complexes are active as antifungals for Candida yeasts and show toxicity for human cells (HeLa) that is dependent on the substitution of N7 of the xanthine moiety. The biscarbene complex 5[NiCp(NHC)2]+is highly selective for Candida glabrata and shows very low toxicity for human cells, being a promising candidate for selective treatment of C. glabrata infections. [ABSTRACT FROM AUTHOR]

Two new spin crossover (SCO) Fe(III) compounds were prepared, their structures were analysed and their magnetic properties were investigated. An exhaustive analysis of the effects of halogen substitution and aromatic ring functionalisation on the magnetic properties of non-solvated Fe(III) perchlorate complexes has been performed. Through comparative analysis, different magnetic profiles were found for the compounds studied, namely F (1), Cl (2), H (3), Br (4a, 4b), and I (5). Using tools like Hirshfeld analysis, the study revealed patterns in octahedral distortions and deviations from the ideal octahedral geometry. The SCO phenomenon as the conducting wire in this study, emphasises the influence of intermolecular interactions on the low spin (LS) to high spin (HS) transitions in these halogen-substituted complexes. The prevalence of H⋯H contributions has been demonstrated, albeit being the weakest and an inverse strength relationship in H⋯X interactions ranging from F to I. The findings not only interpret the intricate balance between halogen substitution, functionalisation, and intermolecular interactions in modulating magnetic properties but also direct future works in designing similar molecular systems. [ABSTRACT FROM AUTHOR]

Dimeric bismuth(III) complexes bearing bis(aryl-imino)acenaphthene (Aryl-BIAN) donor ligands of the general formulae [(Dipp-BIAN)BiCl3]2 2, [(o-iPr-BIAN)BiCl3]2 3, and [(p-iPr-BIAN)BiCl3]2 4, where Dipp = diisopropyl, o-iPr = ortho-isopropyl and p-iPr = para-isopropyl, were prepared by reaction of the corresponding neutral BIAN ligand with BiCl3, under inert atmosphere conditions. X-ray studies were performed, and their molecular structures were determined. The individual contributions of intermolecular interactions to crystal packing have been quantified by means of Hirsfeld surface analysis. [ABSTRACT FROM AUTHOR]

A novel approach has been developed for the efficient synthesis of the unsymmetrical (2-aminopyrrolidin-1-yl)carboxamidine alkaloidal core found in cernumidine (1) and its analogs (20a, 20c, 20f, 20i–o). The key transformation in this process involves the utilization of the Curtius rearrangement, which plays a pivotal role in constructing the aminal moiety. One of the major challenges encountered during this synthesis was the instability of the free aminal core intermediate. Furthermore, a noteworthy observation during the synthesis was the racemization process that occurred during the isocyanate trapping by organometallic reagents. Detailed DFT calculations shed light on this phenomenon, revealing a neighboring coordination-induced mechanism. The resulting compounds were subjected to evaluation for their anti-inflammatory properties using lipopolysaccharide-stimulated human THP1 cells. Notably, compounds featuring the guanidine moiety and electron-donating groups exhibited significant anti-inflammatory activity. These findings suggest that these compounds hold promise as potential candidates for further development as anti-inflammatory agents. [ABSTRACT FROM AUTHOR]

In the present work, several coumarin-3-carboxamides with different azacrown ether moieties were designed and tested as potential luminescent sensors for metal ions. The derivative containing a 1-aza-15-crown-5 as a metal chelating group was found to yield the strongest response for Ca2+ and Pb2+, exhibiting an eight- and nine-fold emission increase, respectively, while other cations induced no changes in the optical properties of the chemosensor molecule. Job's plots revealed a 1:1 binding stoichiometry, with association constants of 4.8 × 104 and 8.7 × 104 M–1, and limits of detection of 1.21 and 8.04 µM, for Ca2+ and Pb2+, respectively. Computational studies suggest the existence of a PET quenching mechanism, which is inhibited after complexation with each of these two metals. Proton NMR experiments and X-ray crystallography suggest a contribution from the carbonyl groups in the coumarin-3-carboxamide fluorophore in the coordination sphere of the metal ion. [ABSTRACT FROM AUTHOR]

Background. Antimicrobial resistance is one of the most pressing health issues of our time. The increase in the number of antibiotic-resistant bacteria allied to the lack of new antibiotics has contributed to the current crisis. It has been predicted that if this situation is not dealt with, we will be facing 10 million deaths due to multidrug resistant infections per year by 2050, surpassing cancer-related deaths. This alarming scenario has refocused attention into researching alternative drugs to treat multidrug-resistant infections. Aims. In this study, the antimicrobial activities of four manganese complexes containing 1,2,3,-triazole and clotrimazole ligands have been evaluated. It is known that azole antibiotics coordinated to manganese tricarbonyl complexes display interesting antimicrobial activities against several microbes. In this work, the effect of the introduction of 1,2,3,-triazole-derived ligands in the [Mn(CO)3(clotrimazole)] fragment has been investigated against one Gram-positive bacterium and five Gram-negative bacteria. Methods. The initial antimicrobial activity of the above-mentioned complexes was assessed by determining the minimum inhibitory and bactericidal concentrations using the broth microdilution method. Growth curves in the presence and absence of the complexes were performed to determine the effects of these complexes on the growth of the selected bacteria. A possible impact on cellular viability was determined by conducting the MTS assay on human monocytes. Results. Three of the Mn complexes investigated (4–6) had good antimicrobial activities against all the bacteria tested, with values ranging from 1.79 to 61.95 µM with minimal toxicity. Conclusions. Due to the increased problem of antibiotic resistance and a lack of new antibacterial drugs with no toxicity, these results are exciting and show that these types of complexes can be an avenue to pursue in the future. [ABSTRACT FROM AUTHOR]

A new neutral dimeric Ar‐BIAN Cu(I) complex (where Ar‐BIAN = bis(aryl‐imino)acenaphthene) of formulation [CuBr(4‐iPrC6H4‐BIAN)]2 (2) was obtained by reacting CuBr and ligand 4‐iPrC6H4‐BIAN (L2) in refluxing acetonitrile under an argon atmosphere. When the ligand used was 2,4,6‐Me3C6H2‐BIAN (L1), we obtained 1 in which the expected dimer (1a) is present, but we could also observe, in solution, the presence of the bis‐chelate dimer [Cu(2,4,6‐Me3C6H2‐BIAN)2][CuBr2] (1b) bearing CuBr2− as counter‐ion; attempts to separate them failed. When the ligand used was 2‐iPrC6H4‐BIAN (L3), we obtained 3 in which the expected dimer (3a) is in equilibrium, in solution, with its bis‐chelate isomer [Cu(2‐iPrC6H4‐BIAN)2][CuBr2] (3b). The solid‐state molecular structures of compounds 2 and 3b were determined by single crystal X‐ray diffraction. The electrochemical behaviour of complexes: 1 (1a, and 1b), 2, and 3 (3a and 3b) and the known compound [Cu(2‐iPrC6H4‐BIAN)2][BF4] (7) were investigated by cyclic voltammetry. The new complexes 1 (1a, 1b), 2, and 3 (3a, 3b) were tested as catalysts for the aerobic oxidation of benzylic alcohols into aldehydes; they all catalyse the reaction, with good results; the catalytic studies were extended to the similar known complexes [CuBr(2,6‐iPr2C6H3‐BIAN)]2 (4), [CuI(2,6‐iPr2C6H3‐BIAN)]2 (5), [CuCl(2,6‐iPr2C6H3‐BIAN)]2 (6) and (7), in order to study the effect of different bridging halides or counter ions in the catalytic activity. We found that compound 4 exhibited a high catalytic activity comparable to the best results published so far. The oxidation products, benzaldehydes, were detected and further confirmed by NMR spectroscopy, and the conversion rate was determined after GC‐FID analysis. [ABSTRACT FROM AUTHOR]

Platinum(II) complexes bearing N‐heterocyclic carbenes based guanosine and caffeine have been synthesized by unassisted C−H oxidative addition, leading to the corresponding trans‐hydride complexes. Platinum guanosine derivatives bearing triflate as counterion or bromide instead of hydride as co‐ligand were also synthesized to facilitate correlation between structure and activity. The hydride compounds show high antiproliferative activity against all cell lines (TC‐71, MV‐4‐11, U‐937 and A‐172). Methyl Guanosine complex 3, bearing a hydride ligand, is up to 30 times more active than compound 4, with a bromide in the same position. Changing the counterion has no significant effect in antiproliferative activity. Increasing bulkiness at N7, with an isopropyl group (compound 6), allows to maintain the antiproliferative activity while decreasing toxicity for non‐cancer cells. Compound 6 leads to an increase in endoplasmic reticulum and autophagy markers on TC71 and MV‐4‐11 cancer cells, induces reductive stress and increases glutathione levels in cancer cells but not in non‐cancer cell line HEK‐293. [ABSTRACT FROM AUTHOR]

A polymorph of glycyl-L-alanine HI.H2O is synthesized from chiral cyclo-glycyl-L-alanine dipeptide. The dipeptide is known to show molecular flexibility in different environments, which leads to polymorphism. The crystal structure of the glycyl-L-alanine HI.H2O polymorph is determined at room temperature and indicates that the space group is polar (P21), with two molecules per unit cell and unit cell parameters a = 7.747 Å, b = 6.435 Å, c = 10.941 Å, α = 90°, β = 107.53(3)°, γ = 90° and V = 520.1(7) Å3. Crystallization in the polar point group 2, with one polar axis parallel to the b axis, allows pyroelectricity and optical second harmonic generation. Thermal melting of the glycyl-L-alanine HI.H2O polymorph starts at 533 K, close to the melting temperature reported for cyclo-glycyl-L-alanine (531 K) and 32 K lower than that reported for linear glycyl-L-alanine dipeptide (563 K), suggesting that although the dipeptide, when crystallized in the polymorphic form, is not anymore in its cyclic form, it keeps a memory of its initial closed chain and therefore shows a thermal memory effect. Here, we report a pyroelectric coefficient as high as 45 µC/m2K occurring at 345 K, one order of magnitude smaller than that of semi-organic ferroelectric triglycine sulphate (TGS) crystal. Moreover, the glycyl-L-alanine HI.H2O polymorph displays a nonlinear optical effective coefficient of 0.14 pm/V, around 14 times smaller than the value from a phase-matched inorganic barium borate (BBO) single crystal. The new polymorph displays an effective piezoelectric coefficient equal to d e f f = 280   p C N − 1 , when embedded into electrospun polymer fibers, indicating its suitability as an active system for energy harvesting. [ABSTRACT FROM AUTHOR]

Herein, we present the synthesis of three new neutral aryl-BIAN ZnCl2 complexes (where aryl-BIAN = bis(aryl-imino)acenaphthene) with formulations [Zn(4-iPrC6H4-BIAN)Cl2] (1), [Zn(2-iPrC6H4-BIAN)Cl2] (2) and [Zn(4-NO2C6H4-BIAN)Cl2] (3) obtained through a green synthesis methodology. Compounds 1 and 2 were fully characterized by elemental analysis, ESI-LS mass spectrometry, FT-IR ATR mode, and multinuclear NMR spectroscopic techniques. Compound 3 was characterized by elemental analysis, ESI-LS mass spectrometry and FT-IR, ATR mode. The solid-state molecular structures of compounds 1 and 2 were determined by single crystal X-ray diffraction. The new complexes 1, 2 and 3, and the known complexes of formulations [Zn(2,6-iPr2C6H3-BIAN)Cl2] (4) and [Zn(2,4,6-Me3C6H2-BIAN)Cl2] (5) were tested as catalysts in the cycloaddition reaction of CO2 and epoxides using the tetrabutylammonium bromide salt as a co-catalyst. Primary studies revealed that complex 4 presented the highest catalytic activity among all synthetized complexes. Good reaction TOFs were obtained for the conversion of propylene oxide (112 h−1) after 3 hours and for the conversion of styrene oxide (23 h−1) after 8 hours, at 4 MPa and 333 K. For more sterically hindered cyclohexene oxide, no cyclic carbonate formation was observed, under the same operational conditions. Furthermore, the effect of reaction time (1–40 h), pressure (0.5–40 MPa) and nucleophile to metal ratio (0.5–100) on final cyclic carbonate formation was investigated. [ABSTRACT FROM AUTHOR]

A series of nine cationic heteroleptic aryl-BIAN-copper(I) (BIAN = bis-iminoacenaphthene) complexes with the general formula [Cu((E-C6H4)2BIAN)(PPh3)2][X] (E = p-Me, p-iPr, o-iPr; X = BF4, OTf, NO3) 1X–3X were synthesized and fully characterized using several analytical techniques, including NMR spectroscopy and single-crystal X-ray diffraction. Except for complexes 2BF4 and 3BF4, which were already reported in our previous works, all remaining complexes are herein described for the first time. Two different strategies were used for the preparation of the complexes: complexes bearing BF4− or OTf− counter-ions (1BF4, 1OTf, 2OTf, and 3OTf) were obtained using the appropriate copper(I) precursors [Cu(NCMe)4][BF4] or [Cu(NCMe)4][OTf], whereas for derivatives 1NO3–3NO3, [Cu(PPh3)2NO3] was used. Their activity as catalysts for the copper azide-alkyne cycloaddition (CuAAC) was assessed alongside other high activity, previously reported Cu(I) complexes. Comparative studies to determine the influence of the counter-ion and of the aryl substituents were performed. All complexes behaved as active catalysts under neat reaction conditions, at 25 °C and in short reaction times without requiring the use of any additive, with complex 2NO3 being the most efficient derivative, along with other NO3−-bearing complexes. [ABSTRACT FROM AUTHOR]

Complexes [Fe(X-salEen)2]BPh4·DMF, with X = Br (1), Cl (2), and F (3), were crystallised from N,N′-dimethylformamide with the aim of understanding the role of a high boiling point N,N′-dimethylformamide solvate in the spin crossover phenomenon. The counter ion was chosen for only being able to participate in weak intermolecular interactions. The compounds were structurally characterised by single crystal X-ray diffraction. Complex 1 crystallised in the orthorhombic space group P212121, and complexes 2 and 3 in the monoclinic space group P21/n. Even at room temperature, low spin was the predominant form, although complex 2 exhibited the largest proportion of the high-spin species according to both the magnetisation measurements and the Mössbauer spectra. Density Functional Theory calculations were performed both on the periodic solids and on molecular models for complexes 1–3 and the iodide analogue 4. While all approaches reproduced the experimental structures very well, the energy balance between the high-spin and low-spin forms was harder to reproduce, though some calculations pointed to the easier spin crossover of complex 2, as observed. Periodic calculations with the functional PBE led to very similar ΔEHS-LS values for all complexes but showed a preference for the low-spin form. However, the single-point calculations with B3LYP* showed, for the model without solvate, that the Cl complex should undergo spin crossover more easily. The molecular calculations also reflected this fact, which was more clearly defined when the cation–anion–solvate model was used. In the other models there was not much difference between the Cl, Br, and I complexes. [ABSTRACT FROM AUTHOR]

Herein, we describe the synthesis of a wide variety of imines through oxidative coupling of alcohols and aromatic amines catalyzed by Mn complexes bearing N^N triazole ligands. A wide variety of imines in excellent yields (up to 99%) have been prepared. Mn-based catalysts proved to be highly efficient and versatile, allowing for the first time the preparation of several imines containing N-based heterocycles. [ABSTRACT FROM AUTHOR]

New manganese complexes bearing di-triazolylidene (di-trz) ligands are described. Depending on the wingtip substituents of the triazolylidene ligand and the synthetic procedure, two different ligand coordination modes were observed, i.e, bridging and chelating. A series of Mn(I) complexes of the general type fac-[Mn(di-trzR)(CO)3Br] (R = Me, Et, Mes) with a chelating di-trz ligand were prepared via Ag-transmetalation. In contrast, the in situ deprotonation of the triazolium salts with KOBut yielded the bimetallic Mn(0) complexes [Mn2(CO)8(μ-di-trzR)] with a bridging di-trz ligand when short alkyl chains (Me, Et, i-Pr) are present as the N1 substituents of the triazolylidene ligand. The molecular structures of monometallic and bimetallic complexes were determined by X-ray diffraction studies. In addition, the cationic fac-[Mn(di-trzEt)(CO)2(PPh3)2]Br complex, a rare example of a dicarbonyl Mn(I) N-heterocyclic carbene, was obtained when fac-[Mn(di-trzEt)(CO)3Br] was irradiated with visible light in the presence of PPh3. The crystal structure revealed a slightly distorted octahedral geometry around the Mn(I) centre, with the chelating di-triazolylidene ligand situated in trans position to the two CO ligands in the equatorial plane, and the two phosphine ligands occupying the axial positions. Cyclic voltammetry studies show reversible redox processes for the monometallic Mn(I) complexes, and a quasi-reversible EC mechanism for the oxidation of the bimetallic complexes. Infrared spectroelectrochemical studies along with DFT calculations for fac-[Mn(di-trzEt)(CO)3Br] suggest that the observed two consecutive reductions both occur at the metal centre. [ABSTRACT FROM AUTHOR]

A group of new boron complexes [BPh2{κ2N,N′-NC4H3-2-C(H)＝N-C6H4X}] (X = 4-Cl 4c, 4-Br 4d, 4-I 4e, 3-Br 4f, 2-Br 4g, 2-I 4h) containing different halogens as substituents in the N-aryl ring have been synthesized and characterized in terms of their molecular properties. Their photophysical characteristics have been thoroughly studied in order to understand whether these complexes exhibit an internal heavy-atom effect. Phosphorescence emission was found for some of the synthesized halogen-substituted boron molecules, particularly for 4g and 4h. DFT and TDDFT calculations showed that the lower energy absorption band resulted from the HOMO to LUMO (π–π*) transition, except for 2-I 4h, where the HOMO−1 to LUMO transition was also involved. The strong participation of iodine orbitals in HOMO−1 is reflected in the calculated absorption spectra of the iodine derivatives, especially 2-I 4h, when spin–orbit coupling (SOC) was included. Organic light-emitting diodes (OLEDs) based on these complexes, in the neat form or dispersed in a matrix, were also fabricated and tested. The devices based on films prepared by thermal vacuum deposition showed the best performance. When neat complexes were used, a maximum luminance (Lmax) of 1812 cd m−2 was obtained, with a maximum external quantum efficiency (EQEmax) of 0.15%. An EQEmax of ca. 1% along with a maximum luminance of 494 cd m−2 were obtained for a device fabricated by co-deposition of the boron complex and a host compound (1,3-bis(N-carbazolyl)benzene, mCP). [ABSTRACT FROM AUTHOR]

Anthocyanins and related flavylium derivatives exist in aqueous solution as a pH-dependent mole fraction distribution of species (a multistate system) with known biological activity. Introduction of nitrogen heterocycles in the flavylium core can lead to multistates with different constitution and increased activity. Compound 1, a diethylamino derivative of 4-pyridinechalcone, was synthesized and characterized by X-ray crystallography, showing a pH-dependent reaction network similar to anthocyanins and related compounds. The several species present at the equilibrium multistate were fully characterized by 1H NMR and 13C NMR. The thermodynamics and kinetics of the multistate were studied through pH jumps followed by 1H NMR and UV-vis absorption including stopped-flow for the faster kinetic steps. In the parent 4-pyridinechalcone compound, protonation of the pyridine nitrogen for pH < 4 prevents formation of the flavylium cation. In compound 1, the first protonation takes place in the diethylamino substituent and in acidic medium, two new flavylium derivatives, a single (2 < pH < 4) and a double (pH < 1) positively charged species, in equilibrium with protonated hemiketal, cis and trans chalcones, have been characterized. Differently from anthocyanins and related compounds, experimental evidence for an unexpected very slow (0.0003 s−1) ring opening-closure between the hemiketal and the cis-chalcone (tautomerization) was achieved. [ABSTRACT FROM AUTHOR]

A group of new mononuclear boron chelate compounds [BPh2{κ2N,N′-5-R-NC4H2-2-C(H)＝N–Ar}] (R = Ar = C6H57; R = C6H5, Ar = 2,6-iPr2C6H38; R = Anthracen-9-yl (Anthr), Ar = C6H59; R = Anthr, Ar = 2,6-iPr2C6H310) were synthesized via the reaction of B(C6H5)3 with the corresponding 5-substituted 2-(N-arylformimino)pyrrole ligand precursors 3–6. These complexes were prepared in order to evaluate the luminescence potential derived from the substitution of the position 5 of the pyrrolyl ring with an aromatic group. Compounds 7–10 were photophysically characterized in solution and in the solid state. The 5-phenyl-2-iminopyrrolyl-BPh2 complexes 7 and 8 are blue emitters and have enhanced photoluminescence quantum yields in the solid state (ΦPL) up to 0.95, whereas the 5-anthracenyl derivatives 9 and 10 have green-bluish fluorescence and a ΦPL of 0.49 and 0.24, respectively. DFT and TDDFT studies were performed, considering the effect of solvent and dispersion, in order to show how the geometries of compounds 7–10 changed from the ground to the excited state, to assign electronic transitions, and to rationalize the observed luminescence. These materials were applied in organic light-emitting diodes (OLEDs), with various device structures, the best showing an external quantum efficiency of 2.75% together with a high luminance of 23 530 cd m−2. [ABSTRACT FROM AUTHOR]

The synthesis of carbocyclic‐fused chromene derivatives based on allene chemistry is described. The phosphane‐catalyzed [3+2] annulation reactions of allenic esters with 3‐nitrochromenes have been established affording 3a‐nitro‐tetrahydrocyclopenta[c]chromenes in good yields (up to 87 %) with high stereo‐ and regioselectivity. Quantum chemical calculations, carried out at the DFT level of theory, were in agreement with the observed selectivity. The trichlorosilane‐mediated reduction of the 3a‐nitro‐tetrahydrocyclopenta[c]chromenes into the corresponding amines is also reported. [ABSTRACT FROM AUTHOR]

A family of mono(2-iminopyrrolyl) complexes with the general formula [Ni{κ2N,N′-5-(aryl)-NC4H2-2-C(H)=N-2,6-(aryl)}(C6H5)(PPh3)] were obtained from the reaction of the sodium salts of the newly synthesised 5-aryl-2-(N-arylformimino)pyrroles with the square planar complex trans-[Ni(C6H5)(PPh3)2Cl]. These new iminopyrrole ligand precursors, designed with increasing bulkiness and different electronic properties, and their corresponding nickel(ii) complexes were characterised by NMR spectroscopy and elemental analysis, and their structural features were analysed by single crystal X-ray diffraction. The nickel complexes were tested as aluminium-free catalysts for the polymerisation of ethylene, at low to moderate pressures and different temperatures and in the absence or presence of the phosphine scavenger [Ni(COD)2], giving rise to catalytic activities in the range of 3.61–73.12 kgPE molNi−1 h−1 bar−1. The polyethylene products formed in these catalytic reactions were characterised by GPC/SEC and NMR spectroscopy. Generally, low molecular weight (Mn 510–1300 g mol−1) low viscosity oils were obtained, presenting high branching degrees (80–125 branches per 1000 C atoms), which are characteristic of hyperbranched polyethylene products. In particular, polymerisation reactions using catalyst 7 led to higher viscosity oils with molecular weights between 11 000 and 20 000 g mol−1, and branching degrees of 100–120 branches per 1000 C atoms. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of an oxidovanadium(iv) [VIVO(L)(acac)] (1) and of two dioxidovanadium(v) [VVO2(L′)] (2) and [VVO2(L)] (2a) complexes of the Schiff base formed from the reaction of 4-(p-fluorophenyl) thiosemicarbazone with pyridine-2-aldehyde (HL) are described. The oxidovanadium(iv) species [VIVO(L)(acac)] (1) was synthesized by the reaction of VIVO(acac)2 with the thiosemicarbazone HL in refluxing ethanol. The recrystallization of [VIVO(L)(acac)] (1) in DMF, CH3CN or EtOH gave the same product i.e. the dioxidovanadium(v) complex [VVO2(L)] (2a); however, upon recrystallization of 1 in DMSO a distinct compound [VVO2(L′)] (2) was formed, wherein the original ligand L− is transformed to a rearranged one, L′−. In the presence of DMSO the ligand in complex 1 is found to undergo methylation at the carbon centre attached to imine nitrogen (aldimine) and transformed to the corresponding VVO2-species through in situ reaction. The synthesized HL and the metal complexes were characterized by elemental analysis, IR, UV–Vis, NMR and EPR spectroscopy. The molecular structure of [VVO2(L′)] (2) was determined by single crystal X-ray crystallography. The methylation of various other ligands and complexes prepared from different vanadium precursors under similar reaction conditions was also attempted and it was confirmed that the imine methylation observed is both ligand and metal precursor specific. Complexes 1 and 2 show in vitro insulin-like activity against insulin responsive L6 myoblast cells, higher than VIVO(acac)2, with complex 1 being more potent. In addition, the in vitro cytotoxicity studies of HL, and of complexes 1 and 2 against the MCF-7 and Vero cell lines were also done. The ligand is not cytotoxic and complex 2 is significantly more cytotoxic than 1. DAPI staining experiments indicate that an increase in the time of incubation and an increase of concentration of the complexes lead to the increase in cell death. [ABSTRACT FROM AUTHOR]

The combination of [Co(II){κ2N,O-NC4H3-C(H)=O}2(PMe3)2] (1) and tert-butyl-α-bromoisobutyrate (tBiB-Br) is a suitable initiation system for controlling the radical polymerization of styrene, by an atom transfer radical polymerization (ATRP) mechanism, below 70 °C and of methyl methacrylate, by an organometallic mediated radical polymerization (OMRP)/catalytic chain transfer (CCT) interplay mechanism, below 50 °C. The pure ATRP nature of styrene polymerization allowed the synthesis of the polystyrene-b-poly(methyl methacrylate) block copolymer, as confirmed by GPC/SEC and DOSY NMR studies. Attempts to isolate a Co(iii) species containing a Br atom (Co(iii)–Br), supposedly a key ATRP deactivator, by reacting 1 and tBiB-Br quantitatively afforded the cationic Co(iii) complex [Co(III){κ2N,O-NC4H3-C(H)=O}2(PMe3)2]Br (2). Metathetic exchange reactions of complex 2 with TlX gave rise to analogues of the type [Co(III){κ2N,O-NC4H3-C(H)=O}2(PMe3)2]X (3a, X = BF4−; 3b, X = BPh4−), containing non-coordinating anions. In the absence of a radical initiator, complex 2 mediated the formation of polystyrene and poly(methyl methacrylate), with poor control, likely via a generation of activators by a monomer addition (GAMA) mechanism. Complexes 3a and 3b, however, have been shown to be completely inactive. Addition of 0.5 equivalents of AIBN to 2 drastically improved the molecular weight control in the polymerization of styrene, at 70 °C, through a reverse-ATRP mechanism. [ABSTRACT FROM AUTHOR]

A series of new cationic Rn-substituted-indenyl nickel(II) complexes containing arsine or stibine ligands were synthesized in moderate to very high yields by the protonation of the corresponding bis(indenyl) nickel derivatives [Ni(η-Rn- Ind)2] with HBF4, in the presence of 2 equiv. of AsPh3 or SbPh3 donor ligands. These complexes, with the general formula [Ni(η- Rn-Ind)(EPh3)2]BF4 (E = As, Sb), were structurally characterized by NMR spectroscopy and X-ray diffraction, and subsequently tested as single-component catalysts for the oligomerization of styrene, leading to the formation of very low molecular weight head-to-tail oligomers (typically consisting of dimers, trimers and tetramers). The new 1- or 2-monosubstituted-indenyl NiII catalyst precursors exhibit extremely high catalytic activities, considerably higher than those observed for the symmetrical unsubstituted- and the 1,3-disubstituted-indenyl nickel analogues (i.e. monosubstituted >> non-substituted > 1,3-disubstituted), their reactivity pattern showing similarities with that of the corresponding allyl derivatives. A simpler and more straightforward experimental procedure for the high yield preparation of [NiBr2(DME)], an important nickel starting material, which was used in the preparation of the bis(indenyl) nickel precursors of this work, is also described. [ABSTRACT FROM AUTHOR]

The conformational properties and the photochemical behaviour of a 2-(1H-tetrazol-1-yl)thiophene were studied using low-temperature matrix isolation (argon; 16 K) coupled with infrared spectroscopy. The experimental results were supported by theoretical calculations carried out at the B3LYP/6-311++G(d,p) level. The calculations predicted two conformers for the studied compound in the gas phase that differ in energy by 3.2 kJ mol−1. Accordingly, two conformers were observed in the low-temperature matrix. UV-laser irradiation at 245 nm of the studied compound isolated in the argon matrix led to photocleavage of the tetrazole ring, with elimination of N2 and formation of the corresponding thiophen-2-ylcarbodiimide, most likely via the corresponding imidoylnitrene intermediate. The flash vacuum pyrolysis of 2-(1H-tetrazol-1-yl)thiophene gave methyl 1H-thieno[2,3-d]imidazole-1-carboxylate via intramolecular formal insertion into a C–C bond of the corresponding imidoylnitrene intermediate and the unexpected 2-methoxythieno[2,3-d]pyrimidin-4(3H)-one. The synthesis of this heterocycle was rationalized considering the initial N2 elimination to generate an imidoylnitrene followed by rearrangement to the corresponding thiophen-2-ylcarbodiimide, [1,5] sigmatropic shift of the methoxyl group and electrocyclic ring closure. [ABSTRACT FROM AUTHOR]

The condensation reactions of 2-formylindole (1) or 2-formylphenanthro[9,10-c]pyrrole (2) with various aromatic amines afforded the corresponding phenyl or phenanthrene ring fused mono-/bis-iminopyrrole ligand precursors 3–8, which, upon reaction with BPh3 in an appropriate molar ratio, led to the new mono- and diboron chelate compounds Ph2B[NC8H5C(H)=N-2,6-Ar] (Ar = 2,6-iPr2C6H39; C6H510), Ph2B[(NC8H5C(H)=N)2-1,4-C6H4]BPh211, Ph2B(NC16H9C(H)=N-Ar) (Ar = 2,6-iPr2C6H312; C6H513), and Ph2B[(NC16H9C(H)=N)2-1,4-C6H4]BPh214, respectively. Boron complexes 12–14, containing a phenanthrene fragment fused to the pyrrolyl C3–C4 bond, are highly fluorescent in solution, with quantum efficiencies of 37%, 61% and 58% (in THF), respectively, their emission colours ranging from blue to orange depending on the extension of π-conjugation. Complexes 9–11, containing a benzene fragment fused to the pyrrolyl C4–C5 bond, are much weaker emitters, exhibiting quantum efficiencies of 10%, 7% and 6%, respectively. DFT and TDDFT calculations showed that 2,6-iPr2C6H3N-substituents or, to a smaller extent, the indolyl group prevent a planar geometry of the ligand in the excited state and reveal the existence of a low energy weak band in all the indolyl complexes, which is responsible for the different optical properties. Non-doped single-layer light-emitting diodes (OLEDs) were fabricated with complexes 9–14, deposited by spin coating, that of complex 13 revealing a maximum luminance of 198 cd m−2. [ABSTRACT FROM AUTHOR]

New indenyl nickel(ii) complexes bearing arsine or stibine ligands synthesised by a new methodology exhibit very high catalytic activities for the oligomerisation of styrene. [ABSTRACT FROM AUTHOR]

A family of 5-(substituted phenyl)-2-formylpyrrole compounds, exhibiting different electronic and steric features at the phenyl ring, was synthesised through the formylation reaction of the corresponding 2-(substituted phenyl)pyrrole precursors, using Vilsmeier–Haack acylation conditions. The products were obtained in moderate to high yields, being systematically characterised by NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. The corresponding crystalline packings were discussed on the basis of three types of arrangements, leading to the formation of dimers, polymers or the newly observed tetramers, all of them essentially governed by strong N–H…O hydrogen bonding interactions. Important C–H…O, C–H…π, π…π and, in the case of fluorinated compounds, C–H…F interactions also contributed to the growth of the three-dimensional crystalline network. DFT calculations helped to rationalise the relationship between the steric and electronic properties of the molecules and the basic units observed in the corresponding solid state structures. [ABSTRACT FROM AUTHOR]

New bis- and tris(iminopyrrole)-functionalized linear (1,2-(HNC4H3-C(H)N)2-C6H4 ( 2), 1,3-(HNC4H3-C(H)N)2-C6H4 ( 3), 1,4-(HNC4H3-C(H)N)2-C6H4 ( 4), 4,4′-(HNC4H3-C(H)N)2-(C6H4-C6H4) ( 5), 1,5-(HNC4H3C-(H)N)2-C10H6 ( 6), 2,6-(HNC4H3C-(H)N)2-C10H6 ( 7), 2,6-(HNC4H3C-(H)N)2-C14H8 ( 8)) and star-shaped (1,3,5-(HNC4H3-C(H)N-1,4-C6H4)3-C6H3 ( 9)) π-conjugated molecules were synthesized by the condensation reactions of 2-formylpyrrole ( 1) with several aromatic di- and triamines. The corresponding linear diboron chelate complexes (Ph2B[1,3-bis(iminopyrrolyl)-phenyl]BPh2 ( 10), Ph2B[1,4-bis(iminopyrrolyl)-phenyl]BPh2 ( 11), Ph2B[4,4′-bis(iminopyrrolyl)-biphenyl]BPh2 ( 12), Ph2B[1,5-bis(iminopyrrolyl)-naphthyl]BPh2 ( 13), Ph2B[2,6-bis(iminopyrrolyl)-naphthyl]BPh2 ( 14), Ph2B[2,6-bis(iminopyrrolyl)-anthracenyl]BPh2 ( 15)) and the star-shaped triboron complex ([4′,4′′,4′′′-tris(iminopyrrolyl)-1,3,5-triphenylbenzene](BPh2)3 ( 16)) were obtained in moderate to good yields, by the treatment of 3- 9 with B(C6H5)3. The ligand precursors are non-emissive, whereas most of their boron complexes are highly fluorescent; their emission color depends on the π-conjugation length. The photophysical properties of the luminescent polyboron compounds were measured, showing good solution fluorescence quantum yields ranging from 0.15 to 0.69. DFT and time-dependent DFT calculations confirmed that molecules 10 and 16 are blue emitters, because only one of the iminopyrrolyl groups becomes planar in the singlet excited state, whereas the second (and third) keeps the same geometry. Compound 13, in which planarity is not achieved in any of the groups, is poorly emissive. In the other examples ( 11, 12, 14, and 15), the LUMO is stabilized, narrowing the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO), and the two iminopyrrolyl groups become planar, extending the size of the π-system, to afford green to yellow emissions. Organic light-emitting diodes (OLEDs) were fabricated by using the new polyboron complexes and their luminance was found to be in the order of 2400 cd m−2, for single layer devices, increasing to 4400 cd m−2 when a hole-transporting layer is used. [ABSTRACT FROM AUTHOR]

The reactivity of azafulvenium methides with internal dipolarophiles was explored as an approach to new chromene derivatives. 4,5-Dimethoxycarbonyl- and 5-ethoxycarbonyl-4-phenylazafulvenium methides with a prop-2-ynyloxyphenyl substituent are converted into 2-[2-(2 H-chromen-8-yl)vinyl]-1 H-pyrroles through a sequence of rearrangements. 4,5-Dimethoxycarbonylazafulvenium methide with a more-activated dipolarophile as well as the more-activated 5-(trifluoromethyl)azafulvenium methide with an unactivated alkyne could be trapped by [8π+2π] cycloadditions to afford 8,12a-dihydro-6 H-chromeno[4,3- e]indolizines. 5-(Trifluoromethyl)azafulvenium methide with a 2-(3-methoxycarbonylprop-2-enyloxy)phenyl substituent at C-1 participated in both intramolecular [8π+2π] and [4π+2π] cycloadditions to afford heterocycle-fused chromanes. The microwave-induced rearrangements of 3-[2-(prop-2-ynyloxy)phenyl]-1 H,3 H-pyrrolo[1,2- c]thiazoles afforded chiral 3-(2 H-chromen-8-yl)-1 H,3 H-pyrrolo[1,2- c]thiazoles. [ABSTRACT FROM AUTHOR]

Two new Ar-BIAN Cu(II) complexes (where Ar-BIAN = bis(aryl-imino)acenaphthene) of formulations [CuCl2(Mes-BIAN)] (1) (Mes = 2,4,6-Me3C6H2) and [CuCl2(Dipp-BIAN)] (2) (Dipp = 2,6-iPr2C6H3) were synthesised by direct reaction of CuCl2 suspended in dichloromethane with the respective ligands Mes-BIAN (L1) and Dipp-BIAN (L2), dissolved in dichloromethane, under an argon atmosphere. Attempts to obtain these compounds by solubilising CuCl2 in methanol and adding a dichloromethane solution of the corresponding ligand, under aerobic conditions, gave also compound 1, but, in the case of L2, the Cu(I) dimer [CuCl(Dipp-BIAN)]2 (3) was obtained instead of compound 2. The compounds were fully characterised by elemental analyses, MALDI-TOF mass spectrometry, FT-IR, 1H NMR and EPR spectroscopic techniques. The solid-state molecular structures of compounds 1-3 were determined by single crystal X-ray diffraction, showing the expected chelation of the Ar-BIAN ligands and two chloride ligands completing the coordination sphere of the Cu(II) centre. In the case of the complex 1, an intermediate coordination geometry around the Cu(II) centre, between square planar and tetrahedral, was revealed, while the complex 2 showed an almost square planar geometry. The structural differences and evaluation of energetic changes were rationalised by DFT calculations. Analysis of the electrochemical behaviour of complexes 1-3 was performed by cyclic voltammetry and the experimental redox potentials for Cu(II)/ Cu(I) pairs have been compared with theoretical values calculated by DFT in the gas phase and in dichloromethane and methanol solutions. The complex 1 exhibited good activity in the reverse atom transfer radical polymerisation (ATRP) of styrene. [ABSTRACT FROM AUTHOR]

Reactions of 2-( N-arylimino)pyrroles (HNC4H3C(H)N-Ar) with triphenylboron (BPh3) in boiling toluene afford the respective highly emissive N, N′-boron chelate complexes, [BPh2{κ2 N, N′-NC4H3C(H)N-Ar}] (Ar=C6H5 ( 12), 2,6-Me2-C6H3 ( 13), 2,6- iPr2-C6H3 ( 14), 4-OMe-C6H4 ( 15), 3,4-Me2-C6H3 ( 16), 4-F-C6H4 ( 17), 4-NO2-C6H4 ( 18), 4-CN-C6H4 ( 19), 3,4,5-F3-C6H2 ( 20), and C6F5 ( 21)) in moderate to high yields. The photophysical properties of these new boron complexes largely depend on the substituents present on the aryl rings of their N-arylimino moieties. The complexes bearing electron-withdrawing aniline substituents 17- 20 show more intense (e.g., ϕf=0.71 for Ar=4-CN-C6H4 ( 19) in THF), higher-energy (blue) fluorescent emission compared to those bearing electron-donating substituents, for which the emission is redshifted at the expense of lower quantum yields ( ϕf=0.13 and 0.14 for Ar=4-OMe-C6H4 ( 15) and 3,4-Me2-C6H3 ( 16), respectively, in THF). The presence of substituents bulkier than a hydrogen atom at the 2,6-positions of the aryl groups strongly restricts rotation of this moiety towards coplanarity with the iminopyrrolyl ligand framework, inducing a shift in the emission to the violet region ( λmax=410-465 nm) and a significant decrease in quantum yield ( ϕf=0.005, 0.023, and 0.20 for Ar=2,6-Me2-C6H3 ( 13), 2,6- iPr2-C6H3 ( 14), and C6F5 ( 21), respectively, in THF), even when electron-withdrawing groups are also present. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have indicated that the excited singlet state has a planar aryliminopyrrolyl ligand, except when prevented by steric hindrance ( ortho substituents). Calculated absorption maxima reproduce the experimental values, but the error is higher for the emission wavelengths. Organic light-emitting diodes (OLEDs) have been fabricated with the new boron complexes, with luminances of the order of 3000 cd m−2 being achieved for a green-emitting device. [ABSTRACT FROM AUTHOR]

A series of new cationic and neutral (Ar-BIAN)copper(I) complexes [in which Ar-BIAN = bis(aryl)acenaphthenequinonediimine] was synthesised and characterised by elemental analysis, 1D and 2D NMR spectroscopy and single-crystal X-ray diffraction. The cationic complexes of the general formula [Cu(Ar-BIAN) L2]BF4 [ L2 = (PPh3)2 ( 1), dppe ( 2), dppf ( 3), (AsPh3)2 ( 4); Ar = 4- iPrC6H4 ( a), 4-MeOC6H4 ( b), 4-NO2C6H4 ( c), 2- iPrC6H4 ( d), Ph2PCH2CH2PPh2 (dppe), (Ph2PC5H4)2Fe (dppf)] were synthesised by reaction of [Cu(EPh3)4]BF4 (E = P or As) and equimolar amounts of Ar-BIAN ligands, or by reaction of equimolar amounts of [Cu(NCMe)4]BF4, 4- iPrC6H4-BIAN ( a) and diphosphanes dppe or dppf, in dichloromethane, whereas the neutral complexes of the types [CuX(Ar-BIAN)(EPh3)] [X = Cl, E = P ( 5); X = I, E = P ( 6); X = Cl, E = As ( 9)] and [{CuX(Ar-BIAN)}2] [X = Cl ( 7), I ( 8); Ar = a, b, c, d, 2,4,6-Me3C6H2 ( e), 2,6- iPr2C6H3 ( f)] were prepared by reaction of CuCl or CuI with equimolar amounts of Ar-BIAN and EPh3 (E = P, As or Sb) in acetonitrile under reflux conditions. The type of ancillary ligand EPh3 and the aryl substituents on Ar-BIAN play crucial roles in determining the formation of cationic or neutral copper(I) complexes. No copper(I) complexes containing coordinated SbPh3 were isolated; all the corresponding attempts led to dimeric complexes 7 or 8. Most of the complexes crystallised easily. Their study by X-ray diffraction revealed distorted-tetrahedral geometries around the copper(I) centres, which are quite influenced by the various aryl substituents on Ar-BIAN and the ancillary ligands EPh3. All complexes 1- 9 except cationic dppf derivative 3a are active catalysts for cycloaddition reactions of alkynes and azides, and also show good tolerance towards functionalised substituents of alkynes and azides. Among them, the PPh3-coordinated complexes 1, 5 and 6 afforded the highest catalytic activities [turnover frequency = 26.9-45.7 h-1]. [ABSTRACT FROM AUTHOR]

The article focuses on the crystal structures of 2-[(4-flourophenyl)iminomethyl]-pyrrole and 2-[(1H-pyrrol-2-ylmethylidene)-amino]benzonitrile. Pyrrole and its substituted derivatives are five-membered heterocyclic compounds that are used in the applications of anion-binding systems, bioactive molecules and pharmaceuticals. The structures consist of two independent molecules in a asymmetric unit that form dimers through N-H···N hydrogen bonds.